OK to delete an air return?

[AlexGB]

[This is not a DIY -- just a general question before I call my heating contractor for his opinion.]

I'm proposing to add a sliding door at the rear of my dining room that will require the remodeler to either relocate or delete an air return located under the window that currently occupies the location of the new slider. He's leaning toward deleting that air return, but I'm wondering if that's wise.

The house is a 1200 square foot cape with a total of 5 air returns on the first floor and one in the upstairs bedroom. Size of each is about 7" H x 15" W, except for the one in the living room which is about 25" wide. There are 7 supply registers, all 7" x 10" H, on the first floor with two on the upper floor. Furnace is a 70k BTU Rheem Contour, with no a/c currently (although I might add it in the future).

The living room adjoins the dining room and the two rooms are separated only by a large archway, and the dining room is also open to a central hallway that contains one of the smaller air returns. It would appear that the system will still be drawing plenty of air from the remaining returns.

I realize this is tough to answer without seeing the house, or at least a floor plan or picture but I'm just wondering what someone else thinks about this from what I've described here. Thanks.

[sktn77a]

You need to calculate your return air flow with and without the dining room return. Most supplies and returns appear undersized and deleting one may just cross the threshold to produce problems (static pressure, temperature differential, etc).

[jdrob12000]

You can never have too much return, but too little can cause problems.
I would have the return relocated.

[beenthere]

Most houses don't have enough return.

So its unwise to eliminate that one.
Your GC may not care. Its not his heating and cooling that will be messed up. Or his heating and cooling bill that will increase.

[AlexGB]

Your replies are sort of what I'm thinking. My layman's gut instinct says that it should be relocated, not omitted.

Just a follow-up question: Would it be okay to just upsize the nearest return, the one in the hallway, to compensate for the removal of the one in the dining room? Or should the return in question be located somewhere as close as possible to its original location? IOW, how critical is location of returns?

[beenthere]

The location won't matter too much, if any.

But, you may not be able to just make the hallway grille bigger. It will probably need another return bay added in the basement.

[kls-ccc]

Just a thought, why not move the return air down the joist space further. In other words if the joist run E-W and the return is on the west wall, put it in the same space on the east wall. Your heating pro will have to verify that the return is sealed and clear along with other considerations, but its an easy way to maintain return air.

[Brian GC]

Your GC may not care. Its not his heating and cooling that will be messed up. Or his heating and cooling bill that will increase.

… which generally applies to HVAC contractors as well.

To say return placement is irrelevant says you haven’t done your homework, otherwise, how do you explain the added expense of installing multiple returns as described in the OP’s house? Someone who was willing to install six returns thought return placement was important. And the one in question is down low for a heating system...hmm?

[Ed Janowiak]

Someone who was willing to install six returns thought return placement was important.

And it means is he installed 6 returns.

The way air moves hasn't changed since the beginning of time or even the last time this was discussed.

Neither have the reasons for installing low or high returns. No matter how much you wish you can suck heat down from the ceiling with low returns, you still can't. You can push it off with proper duct design and grill selection, but the returns just don't matta.

Low returns for a system installed below, high for a system installed above. Give the air an unobstructed way back to the fan and the system will work.

Alex run your system (heat or ac ) measure the temp difference between a supply and a return. Record the difference.
Tape up the return your thinking about deleting. Run the system again. If there is more than a 1° diff in AC or a 3° diff in heating call an HVAC guy to further investigate whether you can lose that return.

[beenthere]

… which generally applies to HVAC contractors as well.

To say return placement is irrelevant says you haven’t done your homework, otherwise, how do you explain the added expense of installing multiple returns as described in the OP’s house? Someone who was willing to install six returns thought return placement was important. And the one in question is down low for a heating system...hmm?

IF return placement was as important as you think. No ones kitchen or bathrooms would heat or cool right.
Since those rooms generally have no return in them.

Probably all of his returns are low.

[Brian GC]

And it means is he installed 6 returns. That’s what he stated in post #1.

The way air moves hasn't changed since the beginning of time or even the last time this was discussed. Switchable returns center on the principles of air density.
Neither have the reasons for installing low or high returns. No matter how much you wish you can suck heat down from the ceiling with low returns, you still can't. But when the cold air off the floor is removed, the warm air on the ceiling has nowhere else to go but down. “Sucking heat down” was never mentioned. You can push it off with proper duct design and grill selection, but the returns just don't matta.

Low returns for a system installed below, high for a system installed above. Why, to make it easier for the installer? Give the air an unobstructed way back to the fan and the system will work. True, but it works better when the unwanted air is removed first.



Then why would someone go through the trouble and expense of installing multiple returns if their location did not matter? Maybe someone who actually does this type of installation could answer this, because obviously many here do not.

[Brian GC]

IF return placement was as important as you think. No ones kitchen or bathrooms would heat or cool right.
Since those rooms generally have no return in them.



You avoided the question again. Why would an HVAC contractor go through the extra work of installing multiple returns throughout the house if their locations were irrelevant?

[beshvac]

Multiple return paths are great when it prevents closing doors from interupting the return path. Returns have a smaller effect of mixing the air in the room than properly sized and designed supplies.

So, move the return it won't make a bit of difference. Don't eliminate a return if you can help it (as it provides more static pressure for the supplies)

[beenthere]

Why would an HVAC contractor go through the extra work of installing multiple returns throughout the house if their locations were irrelevant?

With the exception of bedrooms when the doors are closed.

Ignorance.

[docholiday]

From my view it's a geographical thing and I am not sure either is wrong. Historically homes in the south dont have a basement to put equipment in so multiple returns would mean either a filter in the crawl space (which would never get changed) or a whole bunch of small filter grilles which becomes expensive for the homeowner.

In the north, with a basement, you sill see more return grilles because it's simple to have your filter at the unit. In northern climates where the home has a boiler and air conditioning was added, the air handler may be in the attic. This is also not a desirable place to have a filter so you might have 1 or two filter grilles in the ceiling.

Yes you will see the occaional house up north with one central return even though there may be a basement, and you may even find a home in the south that has a bunch of room returns, but usuaully the habbit is formed.

The bottom line is, you need to know your airflow and system static. If the loss of the return doesnt negatively affect these numbers then so be it. If it does however, then you will need to compensate and install another grille somewhere else. This of course assumes it's right to start with, which should be calculated in the "Before" scenerio so when it comes to "After" they know how much return to add.

[AlexGB]

Just a thought, why not move the return air down the joist space further. In other words if the joist run E-W and the return is on the west wall, put it in the same space on the east wall. Your heating pro will have to verify that the return is sealed and clear along with other considerations, but its an easy way to maintain return air.

I thought of this, but I can't find any wall space that could be serviced by this particular joist space. If I follow the joist to the nearest opposite wall, I end up in the living room, only a couple inches from the big, double width return. Probably not much point in adding a return in that location, right?

[AlexGB]

A picture being worth 1,000 words -- here's a picture of the room in question. The return in question is just behind the chair on the left, slightly to the left of center of the window. The living room is behind you, and just out of sight to the lower right is the hall with a return of its own.

Just one more question: What does anyone think of changing the return below the window to a floor mounted return? Have you had any experience with problems with grilles giving way when people inadvertently step on them, or things falling through the grille?

[Brian GC]

With the exception of bedrooms when the doors are closed.



Huh?

Great explanation.

[DanW13]

So in that pic you have 2 returns ? If that's the case you can probably eliminate the one under the window and carry on with your remodel job. If you need to have more return air just make the one on the right in your pica double return to make up for the one under the window. Or if you wish you can just make that return a floor return, go to your local Habitat Restore and look to see if they don't have any old register return grills, I know in my area they always have some of those older ones, cast iron nice and strong for cheap here they sell for about $20 ea.

[beenthere]

Huh?

Great explanation.
Yes it is.

[AlexGB]

So in that pic you have 2 returns ? If that's the case you can probably eliminate the one under the window and carry on with your remodel job. If you need to have more return air just make the one on the right in your pica double return to make up for the one under the window. Or if you wish you can just make that return a floor return, go to your local Habitat Restore and look to see if they don't have any old register return grills, I know in my area they always have some of those older ones, cast iron nice and strong for cheap here they sell for about $20 ea.

Yes. As I stood there snapping the picture, the other return is over my right shoulder, about 3 feet away, and facing the dining room. Which is why the remodeler seems to think I have adequate return air from the DR, although I think the idea of enlarging that one on my right double size to compensate for loss of the one under the present window.

[seatonheating]

Yes. As I stood there snapping the picture, the other return is over my right shoulder, about 3 feet away, and facing the dining room. Which is why the remodeler seems to think I have adequate return air from the DR, although I think the idea of enlarging that one on my right double size to compensate for loss of the one under the present window.


What he thinks means nothing!! Get an HVAC pro in there to size it properly so you aren't doing it twice or costing yourself more money in the long run.

Why wing it?? Are you not paying this remodeler to do it right?....He's not an HVAC guy and he doesn't really care as stated before.

[Ed Janowiak]

The way air moves hasn't changed since the beginning of time or even the last time this was discussed.


Switchable returns center on the principles of air density.

Ahhh....... now we're getting somewhere. Please explain this in more detail as to how you believe that this works.

I understand that heated air will be come less dense and rise to the ceiling where it will stagnate unless some outside influence moves it. I design systems with properly sized ducts and supply registers to take care of this problem.



Neither have the reasons for installing low or high returns. No matter how much you wish you can suck heat down from the ceiling with low returns, you still can't.


But when the cold air off the floor is removed, the warm air on the ceiling has nowhere else to go but down. “Sucking heat down” was never mentioned.

Please explain how you make heated air "go down" when its lighter than the cooler air you want it to replace? Lighter things will rise won't they? It's that density thing remember, you said that is how these high low set-ups work :yes:.


You can push it off with proper duct design and grill selection, but the returns just don't matta.

Low returns for a system installed below, high for a system installed above. Why, to make it easier for the installer? Give the air an unobstructed way back to the fan and the system will work.


True, but it works better when the unwanted air is removed first.

Again I'll ask how do we remove the air if a return can only influence air that is about 18 to 20" from it?


Then why would someone go through the trouble and expense of installing multiple returns if their location did not matter? Maybe someone who actually does this type of installation could answer this, because obviously many here do not.

Other than temperature in the testing you have done, what else have you measured?

I've measured temps.
Volume in CFM to the space being conditioned and how fast (FPM) the air is moving. I know how far I can blow the air (both calculated and measured) and know how far the air can get sucked from, please elaborate on how you did your testing. I really want to understand this. :ghug:

[Ed Janowiak]

And just so you don’t think I’m making things up, here are some old (relative… a few months old) of actual measurements.

Aprox 5’ above the register.
http://i591.photobucket.com/albums/ss352/EdJanowiak/DSCF1088.jpg


A little closer
http://i591.photobucket.com/albums/ss352/EdJanowiak/DSCF1087.jpg

A return (low - the system is in the basement) with measured velocity cause we were close.
http://i591.photobucket.com/albums/ss352/EdJanowiak/DSCF1083.jpg

Same return but as soon as we move a short distance away from the grill, no more measured velocity or at least the velocity is below 40 FPM, this is the speed at which this meter stops measuring the velocity.

http://i591.photobucket.com/albums/ss352/EdJanowiak/DSCF1084.jpg

The pics suck, was just learning the camera settings, but they are a bit better than just a photo of a house.:det:

[DanW13]

Ahhh....... now we're getting somewhere. Please explain this in more detail as to how you believe that this works.

I understand that heated air will be come less dense and rise to the ceiling where it will stagnate unless some outside influence moves it. I design systems with properly sized ducts and supply registers to take care of this problem.






Please explain how you make heated air "go down" when its lighter than the cooler air you want it to replace? Lighter things will rise won't they? It's that density thing remember, you said that is how these high low set-ups work :yes:.





Again I'll ask how do we remove the air if a return can only influence air that is about 18 to 20" from it?



Other than temperature in the testing you have done, what else have you measured?

I've measured temps.
Volume in CFM to the space being conditioned and how fast (FPM) the air is moving. I know how far I can blow the air (both calculated and measured) and know how far the air can get sucked from, please elaborate on how you did your testing. I really want to understand this. :ghug:

The reason we have high and low return up here in the Gret White North is during the summer we open the high wall returns to take the heated air off the ceiling, and reversethat in thewinter by closing the high wall return and opening the floor returnsto take in the cold air off the floor.

[Ed Janowiak]

How do you "take the heated or cooled air" from anywhere Dan? I don't get it.

The photos above show the velocity of the air being pushed out a supply, this will influence the air ina room.

The photos also show the velocity and lack there of on a return,unless your right next to a return it's placement will not influence the air, it simply can't. The pics show when we're right next to the grill we get measurable movement, when about 2' away the meter reads 0 FPM.

If air is moving we should be able to measure it's movement right? And it does have to move to take that hot or cold air from where it's objectionable doesn't it?

[duckman373]

If it were that important, no house with one, central return would ever produce comfort. I'd rather have 1, properly sized return, than 10 small returns, whose combined size is inadequate. Total duct design, and sizing is the key.

[DanW13]

Heated air is lighter therefore it will linger up along the upper strasaphere of the ceiling and cooler air will be down low around the seating height area of a room. Do you really believe that even though you measure zero 2 ft. away from a return doesn't necessarily mean your not pulling any air from that return on the floor or up along the ceiling ?

When the supply air pushes upward and mixes with the rest of the room air where does the cold air and warm air go ? When I turn my fan on med speed I'm pulling alot of air from my returns and when I'm sitting here at my Mac I have a return around the corner from me (approx 6') I can fell the air movement being pulled into that return, explain that ? And when I run hte fan once in awhile in high speed I can really feel the air movement from the center of the room or anywhere for that matter. IMO it's more important to have the supply placement right than it is to have the return placement but that doesn't mean having high wall and low return not make a difference, it does. Have you ever been in a home with both high and low returns ? or is it that ever home you've been in only had one or the other and never both ? I'm not trying to be a Smart Ass here I'm just telling you my experience as Iv'e lived with them in this type of set-up all my life.

[Brian GC]

Another way of looking at it: A low return will not directly affect the air across the room like a supply register will. But it will move/remove more air than any supply.

When the air in front of a return is removed it is replaced by the surrounding air. Because air density keeps the lighter/hotter air high in the room the removed air is replaced by air in the same strata, or elevation. That is how a low return will remove the cold air along the floor first at the rate and sum total of all supply registers. Once the colder air is removed off the floor the lighter/hotter air has nowhere else to go but down.

Brian

[Shophound]

Another way of looking at it: A low return will not directly affect the air across the room like a supply register will. But it will move/remove more air than any supply.

Incorrect, if I'm reading what you say correctly. A return removes more air from the same room the supply grill serves? If so, how?

If a room does not have adequate return air provision, and as a result becomes pressurized by the supply register (such as when the door is closed), the net volume of supply air to whatever meager return provision is in place (such as a door undercut) is imbalanced. The pressurized room will blow air out through the envelope and subsequently outdoors.

Should a dedicated return air provision be in a room with a closed door, and it is correctly sized, it will prevent the room from becoming overly pressurized and blowing conditioned air out through the envelope. It will also allow the supply register to approach its design throw and spread characteristics, which will assure optimal mixture of air in the room, resulting in a lower temperature gradient between floor and ceiling. Additionally, less air blown through the envelope means less air infiltrating the home for make-up air purposes (aside from HRV/ERV or dedicated fresh air intake provisions).


When the air in front of a return is removed it is replaced by the surrounding air. Because air density keeps the lighter/hotter air high in the room the removed air is replaced by air in the same strata, or elevation. That is how a low return will remove the cold air along the floor first at the rate and sum total of all supply registers. Once the colder air is removed off the floor the lighter/hotter air has nowhere else to go but down.
Brian

It will only do so if it cools to where its density increases and it falls. While the return creates a lower pressure zone in front of it, the air nearest the return will replace what the return removes, leaving the upper regions of the room stagnant. To dispel stagant air at the mid to upper level regions of a room, it must be stirred up.

Temperature gradient problems in a room are optimally solved via building envelope modifications, particularly in window quantity and selection, and controlling envelope leakage. If a floor is too cold when the heat is on, it's cold because the envelope is doing a poor job keeping it warm between furnace cycles, and while the furnace is running.

[Ed Janowiak]

Heated air is lighter therefore it will linger up along the upper strasaphere of the ceiling and cooler air will be down low around the seating height area of a room. Do you really believe that even though you measure zero 2 ft. away from a return doesn't necessarily mean your not pulling any air from that return on the floor or up along the ceiling ? Yes I do believe it because I have measured the air movement on the supply side of systems many times and not measured it on the return side many times. I've measured it with accurate meters and not so accurate things like cigarette smoke or more reseantly a smoke pencil (I quit smoking about 6 years ago).

When the supply air pushes upward and mixes with the rest of the room air where does the cold air and warm air go ? It goes where it's pushed and forced to mix by the supply's, not the returns When I turn my fan on med speed I'm pulling alot of air from my returns and when I'm sitting here at my Mac I have a return around the corner from me (approx 6') I can fell the air movement being pulled into that return, explain that ? And when I run hte fan once in awhile in high speed I can really feel the air movement from the center of the room or anywhere for that matter. IMO it's more important to have the supply placement right I'm with you 100% on that than it is to have the return placement but that doesn't mean having high wall and low return not make a difference, it does. And you lose me hereHave you ever been in a home with both high and low returns ? Manyor is it that ever home you've been in only had one or the other and never both ? I'm not trying to be a Smart Ass here I'm just telling you my experience as Iv'e lived with them in this type of set-up all my life. I live in a heating climate and have fixed many homes with airflow issues. I've been at this for over 20 years, some of these years I didn't get it, now I do.

The #1 reason for for the high returns success is that high returns are added and the system works better. The systems work better because more airflow is achieved with the lowering of the return static. This gives the supply more umph which results in better mixing and more uniform temps from floor to ceiling. The placement of the return is given credit, but no before or after air flow measurements were ever taken. So the placement gets the glory, not the simple fact that there is more.



The visual or physical evidence is hard to dispute when you see that smoke blowing 20' away froma supply, and just hanging in the air when it's just 2' from a return. I understand that people believe what they believe, but it's hard to not believe the smoke.

[Brian GC]

The visual or physical evidence is hard to dispute when you see that smoke blowing 20' away froma supply, and just hanging in the air when it's just 2' from a return. I understand that people believe what they believe, but it's hard to not believe the smoke.

The smoke would have to be heated the same as a heater does to mimic how hot air mixes and seperates with cold air in a room.

Brian

[DanW13]

Maybe need to burn a piece of toast in a toaster next to a supply register to mimic the heated smoke to get a true sense of where the hot/warm air moves vs. cold air.

[Shophound]

The smoke would have to be heated the same as a heater does to mimic how hot air mixes and seperates with cold air in a room.

Brian

Nope. Entrainment. Take a smoke puffer..."smoke" in container same temp as room temp. Puff it into the room. It's at room temp. It will migrate toward the supply air stream and mix with it. That's entrainment. The supply air jet creates low pressure areas around it. This will draw room air toward it because of a delta P. The velocity of the suppy jet is focused and narrow, widening as it flies further away from its outlet. It widens and drops as it slows and cools due to room air mixing with it (in the case of heating), but it is still in motion until it reaches terminal velocity. As long as it is in motion it will entrain surrounding air. It can widen, it can sink. Along the entire path it does this, it is entraining surrounding air.

A return does not have the velocity rate equivalent of a jet to entrain room air like a supply jet does. You need to understand this in order to understand why so often the discussion leads back to supply air dynamics.

You keep mentioning air density...if you're going to focus on this you also must consider convective currents and air temperature. Air does not sink as one solid mass, nor does it rise as one. If there's one constant about air, it is that air in motion is seldom laminar. Mostly, it's turbulent, even at slow rates of convection. As long as even one degree of temperature difference exists across the room air there will be convection. Most occupied rooms do better than this...they have microclimate generators such as windows, lamps, electronics, people, pets, etc.

[Brian GC]

Nope. Entrainment. Take a smoke puffer..."smoke" in container same temp as room temp. Puff it into the room. It's at room temp. It will migrate toward the supply air stream and mix with it. That's entrainment. The supply air jet creates low pressure areas around it. This will draw room air toward it because of a delta P. The velocity of the supply jet is focused and narrow, widening as it flies further away from its outlet. It widens and drops as it slows and cools due to room air mixing with it (in the case of heating), but it is still in motion until it reaches terminal velocity. As long as it is in motion it will entrain surrounding air. It can widen, it can sink. Along the entire path it does this, it is entraining surrounding air.


I understand entrained air and how it draws surrounding air into it. But how can heated supply air continue to drop when it is hotter than the surrounding room air. Cigarette smoke continues to rise because it is hotter, right? Refinery smoke continues to rise because it is hotter than the surrounding air. Why wouldn’t heated supply air migrate upwards since it is also hotter than the surrounding air? Inversely, stage smokers generate smoke that drops because it is damp and cold. It seems a “smoker” would have to be placed at the intake of a heating system and be heated to determine where the heated air ultimately goes.



A return does not have the velocity rate equivalent of a jet to entrain room air like a supply jet does. You need to understand this in order to understand why so often the discussion leads back to supply air dynamics.

I understand a return does not immediately affect the air across the room like a supply does, but when a return removes 400 cubic feet of air what air is drawn into that space to replace it? Would it be air at the same strata or air from above (providing there are no air currents)? I say the same strata because there is less resistance.

Brian

[beenthere]

Refinery stacks don't have a ceiling above them.

[Shophound]

I understand entrained air and how it draws surrounding air into it. But how can heated supply air continue to drop when it is hotter than the surrounding room air. Cigarette smoke continues to rise because it is hotter, right? Refinery smoke continues to rise because it is hotter than the surrounding air. Why wouldn’t heated supply air migrate upwards since it is also hotter than the surrounding air? Inversely, stage smokers generate smoke that drops because it is damp and cold. It seems a “smoker” would have to be placed at the intake of a heating system and be heated to determine where the heated air ultimately goes.

Holding the discussion strictly to a room, the hot air emerging from a supply register cools as it mixes with room air that is entrained within the supply jet. Concurrently, the cool room air that is entrained into the supply jet warms as it mixes in. The supply jet does not remain at, say, 120 degrees across the entire length of its throw, spread, and drop. The very fact that it drops is due to the air cooling as it flies away from the supply vent. This concurs with air density, a matter you've raised.

The stage smoke and refinery smoke are not exact comparisons because they're not under the same dynamics as air emerging from a supply register. The refinery smoke will rise until it cools. Have you ever seen smoke from a smokestack rise until it goes horizontal? It either found upper level winds or cooled to the point to where it has the same density as the surrounding air. The fact that you can still see it is due to the particulate matter composing the smoke. Given enough time these particulates settle out and return to earth.

The stage smoke may be dry ice, which explains why it sinks.



I understand a return does not immediately affect the air across the room like a supply does, but when a return removes 400 cubic feet of air what air is drawn into that space to replace it? Would it be air at the same strata or air from above (providing there are no air currents)? I say the same strata because there is less resistance.

Brian

Let's take a room that's 12 x 12 x 8. That room contains 1152 cubic feet of air. A supply register is emitting 150 cubic feet per minute of air into the room. The return air register is intaking 150 cubic feet of air per minute (CFM). Pertaining to input and outflow, the pressurization of this room is neutral, the supply and return are balanced. This is ideal.

Given adequate air mixing and convection within this room, how long will it take the supply and return air team to perform a complete air turnover of this room? About eight minutes, correct? You must consider the entire air volume of a room, not just the supply and return volume rates.

Returns are mainly a guarantee that whatever air the supply register throws into a room, a provision is made for air already in the room to get out. It also assures this same air that leaves becomes conditioned, whether it be heated and/or humidified, or cooled and dehumidified. Rate of air turnover in a room is crucial to that room's comfort. If the return outdraws the supply, the room will go negative and infiltration through the envelope increases. If the supply outflows the return, the room is pressurized and ends up blowing air through the walls and ceiling and out of the house. A net loss of conditioned air that must be made up.

[Brian GC]

Incorrect, if I'm reading what you say correctly. A return removes more air from the same room the supply grill serves? If so, how?

Because supply registers outnumber returns about ten to one. Therefore returns move about ten times more than a single supply register. I realize net intake equals net outlet but not in the room or area the return is located. That room is generally depressurized which drawn air from throughout the house. My assertion is to draw the cold air from across the house since it draws from all rooms and the draw is strata sensitive.


It will only do so if it cools to where its density increases and it falls. While the return creates a lower pressure zone in front of it, the air nearest the return will replace what the return removes, leaving the upper regions of the room stagnant. To dispel stagnant air at the mid to upper level regions of a room, it must be stirred up.

Not necessarily. The stagnant air is the desired warm air, stirring it is one way to get it to drop to the floor. Removing the lower strata of cold stagnant air is the other. Remember, cold air on the floor is replenished by slabs, windows, walls, leaks, drafts, opening doors, etc. So why not remove it first rather than stirring it into the room?

Hypothetically imagine a 16oz glass of water with 60deg water on the lower half and 80deg water on the top half. The objective is to heat all the water to 80deg. You have a 1oz/min pump hooked up to an 80 degree water heater. That slow of a pump would not mix the water regardless of where the intake and outlet were located. Since the bottom, cold water is the unwanted water, would you draw off the bottom to remove the cold water first or would you mix the whole glass and begin removing 70deg water? IMO drawing off the bottom first would require only 8oz of water change to heat all the water to 80deg. To mix the water first would require more than four times the work which would make it far less efficient. Please comment of this example.

Brian

[beenthere]

Your hypothetical situation. Would not be able to heat the bottle of water to 80°F no matter where your pulled the water from. At the pump rate you listed.


But, its a good example of how futile it is for people to try to fix air supply problems with return placement.

[Brian GC]

Refinery stacks don't have a ceiling above them.

As if that has any relevance. Try to keep up here.



Your hypothetical situation. Would not be able to heat the bottle of water to 80°F no matter where your pulled the water from. At the pump rate you listed.


But, its a good example of how futile it is for people to try to fix air supply problems with return placement.

Now you are a Hydro-Specialist?

It would if the room was 80deg. You should learn to ask the right questions before making presumptuous statements and off-topic, uwarranted digs.

See what being sarcastic gets you, just more sarcasm…but maybe you are just bored and enjoy it.

Somebody just said they use high/low returns with good result in a previous post. Why didn’t you jump all over them like you do me? You should learn to spread your love around.

[beenthere]

As if that has any relevance. Try to keep up here.

The ceiling plays a roll in how the air moves. Maybe you should rethink your comparisons, before you make them.




Now you are a Hydro-Specialist?

It would if the room was 80deg. You should learn to ask the right questions before making presumptuous statements and off-topic, uwarranted digs.

See what being sarcastic gets you, just more sarcasm…but maybe you are just bored and enjoy it.

Somebody just said they use high/low returns with good result in a previous post. Why didn’t you jump all over them like you do me? You should learn to spread your love around.

If the room is 80°, then there is no need to use a heater to heat the water at the bottom. Since it would be heated by the room temp.

You try to make things up situations. And then when the answer doesn't suit you.
You change a parameter. Or, try to insult your way around you not knowing what your talking about.


I'm not against high and low returns.

But, I am against your cure all BS you spout about them.

[Brian GC]

If the room is 80°, then there is no need to use a heater to heat the water at the bottom. Since it would be heated by the room temp.

You totally missed the point of the question and the analogy, but that’s OK.


You try to make things up situations. And then when the answer doesn't suit you.
You change a parameter. Or, try to insult your way around you not knowing what you’re talking about.

The water in the glass is a very similar comparison to my point of removing the unwanted substance first. If you don’t get it, that’s OK too.



I'm not against high and low returns.

Why, I thought you said they were of no worth. Maybe you could expand on that thought.


But, I am against your cure all BS you spout about them.

I never said they were a “cure-all”. I said they will help a system when there is less than optimal air circulation, which is the case in most homes I’m in.

Brian

[beenthere]

You totally missed the point of the question and the analogy, but that’s OK.

No, I didn't.



The water in the glass is a very similar comparison to my point of removing the unwanted substance first. If you don’t get it, that’s OK too.

No, it was a bad anology.




Why, I thought you said they were of no worth. Maybe you could expand on that thought.

Just not against them. Don't install them as a rule. But, once in a while. A customer has a silly notion that they are needed. And is willing to pay for them. So I will install them.



I never said they were a “cure-all”. I said they will help a system when there is less than optimal air circulation, which is the case in most homes I’m in.

Brian

You have touted them as the way to make every air system work better.

[Brian GC]

You have touted them as the way to make every air system work better.

Not every one, just every one I've seen.

I have always said that the better the circulation, the less effective low returns on a heating system will be. But, being positioned low can never hinder a system like being mounted high. It can only help it.

Brian

[beenthere]

Don't need high and low returns.

I only have low returns. Heats and cools fine.

[Brian GC]

Don't need high and low returns.

I only have low returns. Heats and cools fine.

Try routing your low return to the highest point in the house and you will probably have the revelation X, me, and others have had. The higher your ceilings and return, the more it will likely hinder your system.

Brian

[tinmandad]

Don't need high and low returns.

I only have low returns. Heats and cools fine.

Same here.
Around here we install low returns.
I don't have any scientific evidence of what's best, but, in 30+ years I've had no complaints.

[Shophound]

Because supply registers outnumber returns about ten to one.

That is a generalization and really isn't the point, is it? If you have one supply register in one room, and a large return air intake at the center of the house for the entire house (which is a very common setup in warm climate homes with slab foundations) you may or may not have pressurization/depressurization issues of each room depending on whether doors are open or closed, or whether each room has sufficient return air provision, such as jump ducts or bypass ducts, to allow sufficient return air to occur from the room when the doors ARE closed.


Therefore returns move about ten times more than a single supply register.

Another generalization. Are you speaking about one central return? Or several smaller returns distributed throughout the house? While one central return might see a volume rate higher than the largest supply register in the house, it can't touch the smallest supply register for velocity.



Not necessarily. The stagnant air is the desired warm air, stirring it is one way to get it to drop to the floor. Removing the lower strata of cold stagnant air is the other. Remember, cold air on the floor is replenished by slabs, windows, walls, leaks, drafts, opening doors, etc. So why not remove it first rather than stirring it into the room?

How about reducing the sources of replenishment, such as better windows, tighter walls, fewer drafts, etc?


Hypothetically imagine a 16oz glass of water with 60deg water on the lower half and 80deg water on the top half. The objective is to heat all the water to 80deg. You have a 1oz/min pump hooked up to an 80 degree water heater. That slow of a pump would not mix the water regardless of where the intake and outlet were located. Since the bottom, cold water is the unwanted water, would you draw off the bottom to remove the cold water first or would you mix the whole glass and begin removing 70deg water? IMO drawing off the bottom first would require only 8oz of water change to heat all the water to 80deg. To mix the water first would require more than four times the work which would make it far less efficient. Please comment of this example.



I used to take care of swimming pools. I'm the type of guy who isn't satisfied knowing just enough about what I set about to do. I'd read about the optimal way to set the supply jets in the pool, and then go do it. I'd read further to understand why. The jets were set in a certain pattern to assure the most thorough turnover of water for circulation and filtration possible for a given pool's configuration. I remember wondering how those small supply jets could somehow turn over the entire pool's water content and assure that at some point all of it passes through the filter. Set correctly, they in conjunction with the one central drain on the bottom, and the skimmers on top (which you and X might well seize upon to illustrate high and low returns :) ...except skimmers are only there to collect floating debris and provide a connection point for vacuuming the pool plaster) turned over the water sufficiently that (with D.E. filters) the water could clear itself overnight if it was somewhat turbid.

That's pretty amazing. A 25,000 gallon swimming pool can change over its entire volume just by little jets and drainage provisions. To wit, so can a house with supply and return air provisions.

Regarding your illustration, if you could get a jar to have 80 degree water on top with 60 degree water on bottom with no natural convective currents already circulating the water, that would be an amazing circumvention of physics.

Convective currents will be in place in any room that has a temperature difference in the air. If the top of the room had 80 degree air and the bottom of the room had 60 degree air, the 80 degree air would migrate toward the 60 degree air, as hot flows to cold. In the exchange of heat the cooler air would rise as it's warmed by the warmer air. The warmer air sinks as it is cooled by giving up heat to the cooler air. Just because the air on the floor isn't suitable for human comfort purposes does not mean it's not in motion due to convection.

[Brian GC]

Another generalization. Are you speaking about one central return? Or several smaller returns distributed throughout the house? While one central return might see a volume rate higher than the largest supply register in the house, it can't touch the smallest supply register for velocity.

My only point was that the single return air extracts the sum total of all supply registers, be it twice or ten times the average supply. Its volume is far greater than the nearby supply registers. Therefore its affect on the central area would be significant if it was removing predominantly heated air when there was cooler air it could be removing instead.


How about reducing the sources of replenishment, such as better windows, tighter walls, fewer drafts, etc?

That is the other half of the equation, but each heater setup should be optimally designed to be the best it can be regardless of existing leaks.


Regarding your illustration, if you could get a jar to have 80 degree water on top with 60 degree water on bottom with no natural convective currents already circulating the water, that would be an amazing circumvention of physics.

Convective currents will be in place in any room that has a temperature difference in the air. If the top of the room had 80 degree air and the bottom of the room had 60 degree air, the 80 degree air would migrate toward the 60 degree air, as hot flows to cold. In the exchange of heat the cooler air would rise as it's warmed by the warmer air. The warmer air sinks as it is cooled by giving up heat to the cooler air. Just because the air on the floor isn't suitable for human comfort purposes does not mean it's not in motion due to convection.

That is why I called it hypothetical. I realize two temps of such deltas could never be so close to each other without convective interaction. But if you could have that condition my question was: would you rather draw off the bottom or stir the water first. I think you know extracting the cold first vs. stirring the water is the obvious and most efficient choice.

If the delta T is confusing and introduces convective principles then imagine the same test but with sediment on the bottom half and clear on top. Objective is to clean the water with a slow pump and filter. Would you draw the dirty water first or stir it first? Again, for quickest results stirring is not recommended for a stratified condition IMO.

Brian

[beenthere]

Try routing your low return to the highest point in the house and you will probably have the revelation X, me, and others have had. The higher your ceilings and return, the more it will likely hinder your system.

Brian
Tried that. made no difference.

My returns are flor returns.
I used thermopan. And created return chases up to 12" from the ceiling, just to see if it would make a difference in the summer.
It didn't.
My supplies throw the air to the ceiling. So I have good air mixure with room air. And it makes no difference summer or winter, for comfort.

If I had no throw from my supplies. Then it would be a way to cover up the problem of incorrect supply registers.

[Shophound]

If I had no throw from my supplies. Then it would be a way to cover up the problem of incorrect supply registers.

You nailed it.

I've said it before and it is worth repeating: no intelligent conversation regarding air distribution throughout a residence can take place without a thorough understanding of both sides of the coin; supply air throw, drop, & spread, entrainment, convective currents within a space, and return influence and sizing. Throw in mean radiant temperature and humidity control for good measure, pertaining to the human comfort dynamic (which is what this entire discussion is for, anyway).

One can dream up a plethora of hypotheticals to favor their section of understanding, but such aren't necessary. The real-time dynamics are observable and do the job handily every day. Let these dynamics be the instructor vs. presupposition.

[Shophound]

My only point was that the single return air extracts the sum total of all supply registers, be it twice or ten times the average supply. Its volume is far greater than the nearby supply registers. Therefore its affect on the central area would be significant if it was removing predominantly heated air when there was cooler air it could be removing instead.

Providing no net loss through the envelope, and an adequate path back to the central return from all zones of the structure, the return will flow around the same volume of air as the aggregate of supplies. It will not, however, flow at the same VELOCITY. You must understand this important difference. Supply drop, throw, and spread receive attention by smart HVAC system designers due to VELOCITY as well as VOLUME. The VOLUME assures the proper amount of BTUs reaches the room to heat or cool it (in essence to offset heat gain or loss through the envelope). The VELOCITY assures air already in the room has an opportunity to interact with the conditioned air injected into the room.

Return paths provide a way for air to reach the air handler for conditioning. Period. That's all they do. You could isolate a room from the house and throw a supply in there without a return, but the only way you're heating or cooling it is shoving a bunch of air through the walls and ceilings to the outdoors. If the room was absolutely airtight, the supply wouldn't flow. It would be equivalent to placing a spray head on a garden hose that can be shut off, or connecting this same hose to a water and airtight tank. It will fill until the pressure within the tank equalizes with the water pressure in the hose. It then stops.




That is the other half of the equation, but each heater setup should be optimally designed to be the best it can be regardless of existing leaks.

To paraphrase Carnak: Building envelopes have a far greater influence over indoor comfort than any HVAC system design can.

We are so conditioned via our outdated construction methods to make up for it by high energy HVAC solutions. Once you experience living in a structure that does not undergo daily rapid changes in temperature and humidity, it changes how you think about building envelopes and HVAC systems. If anything, the HVAC system should be largely for conditioning ventilation air, offsetting internal heat gain (during cooling), and offsetting what reduced amount of heat gain or loss through the envelope occurs during extreme weather conditions. Instead, we have high horsepower HVAC systems struggling to maintain fickle human comfort requirements against Swiss cheese, marginally insulated envelopes full of thermal bridges and bypasses, topped with single pane glazing that are only a razor thin improvement over just leaving a window open.




That is why I called it hypothetical. I realize two temps of such deltas could never be so close to each other without convective interaction. But if you could have that condition my question was:

You can't, so the hypothetical falls apart. Stick to the real stuff. It will bail your butt out every time. :)



If the delta T is confusing and introduces convective principles then imagine the same test but with sediment on the bottom half and clear on top.

No confusion here. I know what those convective currents are doing. They're in force whether the HVAC system runs or does not run. They're one reason a room is comfortable or uncomfortable between HVAC run cycles.


Objective is to clean the water with a slow pump and filter. Would you draw the dirty water first or stir it first?

This is no chicken or egg choice, Brian. You do both. If you draw from the same source, you must pump it back to the same source, unless you want to experience loss through leakage, which most of us tolerate.



Again, for quickest results stirring is not recommended for a stratified condition IMO.

Brian

From a grammar perspective, "stirring" is the opposite of "stratified". Stir up air that is stratified, it is no longer stratified. It is stirred up.

[Brian GC]

Return paths provide a way for air to reach the air handler for conditioning. Period. That's all they do.

Not entirely. They also establish the major are movement within the house. It can probably be witnessed best in a stairway when the return is upstairs. In this case you will see cold air within 12” of the treads moving downward and warmer air hugging the ceiling moving upwards. No matter how well you mix the downstairs air, the air that moves up a stairway toward the return will be the warmest air. 90% of my returns are upstairs so the upward (heat loss) draft is strong. But regardless of this draft, the cold air still falls down the treads. To pull downstairs air upstairs is to remove the warmest of air first and leave the colder floor air intact.



To paraphrase Carnak: Building envelopes have a far greater influence over indoor comfort than any HVAC system design can.

I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.



You can't, so the hypothetical falls apart. Stick to the real stuff. It will bail your butt out every time. :)

The hypothetical part is only to emphasize major stratification, you can imagine that can‘t you? I know 60deg water cannot sit next to 80deg water without influence, but stratification can occur in a house can’t it? In the example like the water in a glass simplifies a demonstration of how to remove the unwanted substance first rather than mixing and having to remove all 16oz many, many times to obtain your goal. In my example 80degrees could be obtained with about 10 – 12oz pumped through the heating system. Stirring the water first would require upwards of 50 - 100oz pumped.

Ideal and simplified (hypothetical) examples are used in the classroom all the time.

I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?



No confusion here. I know what those convective currents are doing. They're in force whether the HVAC system runs or does not run. They're one reason a room is comfortable or uncomfortable between HVAC run cycles.

Natural convective currents do not eliminate stratification.


From a grammar perspective, "stirring" is the opposite of "stratified". Stir up air that is stratified, it is no longer stratified. It is stirred up.

But as my water example shows, major stirring is not always the only or best way to heat a house.

Brian

[Shophound]

Not entirely. They also establish the major are movement within the house.

This point may be the "irreconcialable difference" between us, Brian. As long as you're eagle eyed focus is on return air dynamics, you'll say stuff like this. You have yet to show any indication you comprehend what we've been saying about supply side dynamics.

I see the whole picture. Supply and return. And how the building envelope fits in. I don't claim to have a fully mature understanding of it but I'm getting there. My job requires that I understand airflow dynamics, so I make a point to go beyond mere requirements and understand it in various applications, be it residential or commercial.


It can probably be witnessed best in a stairway when the return is upstairs. In this case you will see cold air within 12” of the treads moving downward and warmer air hugging the ceiling moving upwards. No matter how well you mix the downstairs air, the air that moves up a stairway toward the return will be the warmest air. 90% of my returns are upstairs so the upward (heat loss) draft is strong. But regardless of this draft, the cold air still falls down the treads. To pull downstairs air upstairs is to remove the warmest of air first and leave the colder floor air intact.

Of course this will happen in multi story homes that experience a lot of temperature gradient due to various reasons. The people that complain most bitterly in either single story or multi story homes about temperature imbalances live in high ceilinged, highly windowed, Swiss cheese chimneys. They'll never be comfortable even if they brought a Hollywood wind machine in there to shove all the air around. These homes violate at least two points of my "quartet for indoor comfort" sig line.



I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.

Well sealed isn't the only aspect, albeit a large one. A well sealed, well insulated home that overall reduces heat transfer through the envelope significantly is a big deal, whether the home be single or multi-story.

And why would you even think of designing a poor HVAC system for a house with a great thermal envelope? When you say things like that it comes across as grasping at straws. You may not intend so, but that's how I read it. You weaken your position by appearing desperate to defend it.




Ideal and simplified (hypothetical) examples are used in the classroom all the time.

To illustrate the unfamiliar with the familiar, yes. I prefer examples that closely mimic reality, where it isn't hard for the student to make the connection. I also prefer illustrations that do not confuse concepts.


I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?

My uncle is a retired aerospace engineer. He likely could smoke my knowledge of aerodynamics pertaining to aircraft. However he's not a civil or a mechanical engineer. He asks me questions about HVAC because he knows I swim in it every day.
My specialty is HVAC management for critical environments, in particular an art museum. I not only need to turn wrenches, but understand how my building interacts with the indoor and outdoor environment. I need to understand airflow and heat transfer. Psychrometrics. Building envelopes. The curators and the director like that I know this stuff. So does my boss. I'm currently working on my degree, but that doesn't stop me from applying what I know, and acquiring what I don't know. I don't wait around for someone to tell me...I go find it when I need to know.



Natural convective currents do not eliminate stratification.

As a blanket statement you say so? Or in a given frame of reference? Pertaining to human comfort you may be right. Pertaining to sheer thermodynamics, maybe not.

[Carnak]

I could design a system so poorly that a perfectly sealed house would not heat, so that statement is untrue. Having a well sealed house is not adequate compensation for a poorly designed system. System design is still very important.

I doubt even you could Brian

Try this video out, has a pencil pusher who implemented some of the concepts developed in Canada's Advanced House Program. I was involved in this program, it was the step beyond the R2000 home which are the worlds most energy efficient and readily built homes, a light year beyond the average new construction quality happening in the USA right now.

Anyways in the late 90s there were major Ice Storms in eastern Canada, and this guy was keeping his entire home comfortable with passive solar heat, and a tiny gas fireplace on a millivolt system that just radiated and naturally convected heat. Power was out for about a week in winter conditions. Doubt it was more than 20,000 Btu input

This guy was worried about VOCs over a decade ago.

http://www.science.gc.ca/Videos/Earthtones/Advanced_House-WS34186CAF-1_En.htm?





I do not have an engineering degree but I do have two brothers and a father who are engineers. I have always had that analytical mindset all around me. Not to get too personal but do you have an engineering degree or are you surrounded by engineers?

I know a couple engineers, they design hvac, they are not chemical/electrical engineers with stop watches :)

[Shophound]

Great video! Enjoyable to watch and echoes everything we've been saying here.

[Carnak]

The R2000 program is almost 30 years old now. It is where the concept "the building as a system" came from.

http://r2000.chba.ca/What_is_R2000/brief_history.php

I must of done 50 homes built to this standard myself, and my father twice that many.

The main difference between R2000 homes and houses built to current Canadian codes are issues such as the air tightness are blower door tested as one part of the certification program and with R2000 you had to use heat/energy recovery ventilation.

If you carry 0.07 air changes an hour for natural infiltration on one of these houses you will be conservative in your furnace sizing. The non certified homes you would carry about 0.3 ACH and be conservative.

The Advanced House Program, was diminishing returns when it came to thermal efficiency when compared to R2000. You could not really seal the houses up any tighter and not a big difference if your exterior walls were R30 instead of R22 or your attic was R60 instead of R40. It differed from R2000 mainly because it was a more green building program and focused on more energy efficient lighting and appliances. Advanced house was also into 'integrated mechanical systems" while R2000 just used conventional high efficency systems. - You would not have say "passive solar domestic hot water heating" tied into a forced air or radiant floor heating system in an R2000 home.

In heating climates, a Passive Solar design can greatly reduce heat bills. One home owner with a passive solar R2000 home used to annoy the hell out of me, they were having an intermittent problem with a GSHP system, and would only call to complain at night.

Turned out to be an intermittent short in the transformer windings. I was annoyed as they never called during working hours to complain, always after supper and they were 1 hour drive out of town.

This was happening when the weather was still in the single digits F, not the -20F and colder range that the systems were designed for. When the sun was shining, it actually kept the house warm to the point that the geo never had to run.

They would not know the heat was down until after the sun set.

Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille.

[Carnak]

You could ball park furnaces sizes on new construction, prior to doing a load calculation pretty easily.

Just have to take the total square footage including the basements that were always heated and multiply by about 17 to get the heating requirement of a house built to code.

If it was going to be an R2000 home, just had to multiply by 13.

And this was for homes facing -24 to -30F ambients. Most common furnaces I ever sold were 60 to 75K gas furnaces, 80% and 90% efficiency.

Do the detailed room by room heat loss later in the design stage and almost every single time come up with the furnace sized to meet the "17" & "13" Btu/sq ft allowance. May get stung if they ended up with an atrium of glass or wanted to use a Jenn Air range or fancy Italian Stainless Hood in the Kitchen. Only end up eating a C-note on the ball park quote, the cost of the next larger furnace than what you quickly pre-estimated. and could then more than make it back by adding a 'make up air system' to handle the excessive intermittent exhausts that have no real business in the home in the first place.

It is amazing what you can do when someone builds a home that actually keeps the outdoors 'outside' of the home and you can control how outdoor air moves through the building.

So that is why I say, the way we build has the biggest impact. My own home and three adjoining units down here in the tropics are tight to the R2000 levels and they run some of the lowest indoor humidty levels found anywhere in the humid tropics and significantrly lower than most posts you see in here outside of people in arid regions.

When there are problems it is often the hvac that is the first to blame. A lot of times when you get to the root cause of the problem, it is because the house was a POS when it came to construction quality.

[Shophound]

Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille.


:LOL::LOL:

[Shophound]

It is amazing what you can do when someone builds a home that actually keeps the outdoors 'outside' of the home and you can control how outdoor air moves through the building.

So that is why I say, the way we build has the biggest impact. My own home and three adjoining units down here in the tropics are tight to the R2000 levels and they run some of the lowest indoor humidty levels found anywhere in the humid tropics and significantrly lower than most posts you see in here outside of people in arid regions.

When there are problems it is often the hvac that is the first to blame. A lot of times when you get to the root cause of the problem, it is because the house was a POS when it came to construction quality.

Yep, yup, affirmative, aye, checkmate, slam dunk. :)

Imagine if HVAC design shifted from scattershooting attempts to counteract a poor building envelope to actual, accurate, efficient, and effective indoor climate control with low energy cost and high comfort.

Sure beats going round and round about return air grill locations. :gah:

[DanW13]

"Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille."


Thats because people out in Kalifornia build Paprermachca House's and don't know what Insulation is !!

[Shophound]

"Anyways, when a guy in Canada can keep his house warm in the winter for a week with no power and basically the sun and a 20-30K Btu gas fire place, it just baffles me at how people freeze in California because of a return grille."


Thats because people out in Kalifornia build Paprermachca House's and don't know what Insulation is !!

I had Kalifornia Kulture Shock when I went to work on a house in a Sacramento suburb that was built in the sixties. It used 2 x 3 studs for the walls - all walls - not 2 x 4. Marginal insulation. I lived in California long enough to learn that the "mild climate" everyone raves about can disappear quickly, usually in the searing hot direction, but sometimes it goes cold as well. California generally may not be a humid climate, and it may not experience weeks of extremely hot weather like Phoenix or Dallas, but it should not foster the idea that one can be lax in how one approaches building thermal envelope design or retrofitting. I don't remember any one year in that state being a carbon copy of the other, weather wise, in the twelve years I lived out there. Best motto is "be prepapred".

[Brian GC]

This point may be the "irreconcilable difference" between us, Brian. As long as you're eagle eyed focus is on return air dynamics, you'll say stuff like this. You have yet to show any indication you comprehend what we've been saying about supply side dynamics.

My focus on return air dynamics is not because I feel the thermal envelope or supply disbursement issues are less important. They are very important in indoor comfort and functionality of a heating system, probably more important. But it doesn’t mean just because return placement is third in importance it should be ignored or misunderstood. Poor duct design is a problem of its own and should not be dealt with by improving an envelope, but it could be dealt with by improvements in supply side disbursement if the locations, volume, and fpm of each register is already correct.

I live in a7 year old 3,000 sqft house that is thermally tight to my experience and the heater function is a POS. There is nothing I could do to tighten the envelope to better the functionality of the heater. Because the downstairs heating unit has its return on the upstairs ceiling it draws the warm air off the downstairs ceiling and up the stairway. If the return was downstairs, on the floor, and the furthest away from the stairway it would be a significant improvement. But the HVAC contractor was probably unaware of these principles, as many here are, and probably couldn’t sell the more expensive job unless he was very versed in the theory and the salesmanship.

The upstairs unit has the same problem but to a lesser degree because its returns are on the ceiling as well. It can run for 30 minutes and I know I’m only getting about one third its potential efficiency.

I’ve seen before and after effects of window and door replacement, it’s a good part of my business. Have you seen before and after effects of poor return placement? Just because improving thermal envelopes is a very legitimate fix doesn’t mean it negates other contributing factors in indoor discomfort.


Of course this will happen in multi story homes that experience a lot of temperature gradient due to various reasons.

Put the return downstairs so it pulls air down the stairway instead of up it. The rising heat problem of the two story house would be at least minimized when the unit is on. This would at least allow the house to heat. The worst case I saw was while I was crowning a newly remodeled two story house with new windows, doors, insulation, and heating unit. I watched the unit run for an hour, trying to heat the house, but the large single return at the top of the stairway made the accumulation of heat impossible. The house never heated. I felt sorry for the poor homeowner who just paid for the job.


And why would you even think of designing a poor HVAC system for a house with a great thermal envelope?

I wouldn’t. My point was that a poorly designed heating system is not overcompensated by a tight envelope. A poorly designed system is a poorly designed system, regardless of the envelope.


To illustrate the unfamiliar with the familiar, yes. I prefer examples that closely mimic reality, where it isn't hard for the student to make the connection. I also prefer illustrations that do not confuse concepts.

You know removing the unwanted water first is the correct approach, but you don’t want to say it because you may think it lends credence to my points. I know it isn’t’ directly applicable, but the similarity is close enough.

Brian

[Brian GC]

I doubt even you could Brian.



Carnak,
If you are attempting to invoke a response out of me you can hang it up, I won’t.

Though you may be very good at HVAC in general, I still consider you to be too rude, adversarial, and incomprehensive of the English language to waste my time with. But maybe your fan club gets a kick out of your antics, so carry on.

[Shophound]

My focus on return air dynamics is not because I feel the thermal envelope or supply disbursement issues are less important. They are very important in indoor comfort and functionality of a heating system, probably more important. But it doesn’t mean just because return placement is third in importance it should be ignored or misunderstood. Poor duct design is a problem of its own and should not be dealt with by improving an envelope, but it could be dealt with by improvements in supply side disbursement if the locations, volume, and fpm of each register is already correct.

Supply side? Did you actually say supply side?? Holy smokes we're getting somewhere! :)

I've never advocated ignoring good duct design, nor has anyone else here who understands HVAC system design. We've hit on it repeatedly in these discussions. In reality, the same lack of care that goes into many HVAC installations extends to the building envelope. That's one reason I harp on the latter, as it can be just as blithely ignored as poor duct design and installation. "The house is a system" is not just cliche building science talk, it's a fact.


I live in a7 year old 3,000 sqft house that is thermally tight to my experience and the heater function is a POS. There is nothing I could do to tighten the envelope to better the functionality of the heater.

What measures of tightening have you done? Has a blower door test been conducted on your home? If so, what were the results? If not, have you considered doing this?

What type of windows do you have? Do you live near the coast in California, or further inland? Have you ever performed a heat load calculation on your home, including required room by room airflows? And if so, has actual airflow delivered to each room been verified? Does each room in your home have return provision besides undercut doors?

Did I read correctly that your downstairs unit has its return air in the ceiling of the upstairs hallway over the stairs? If so this isn't really a matter of switchable returns, it's beyond that. It means both return ducts are in the attic for both floors. It means your return ducts and plenums might be (on average, they are) leaky, which could create pressurization/depressurization issues with your house. Have you ever had your house pressure measured in respect to outdoors when your systems run to see if it is going positive or negative in respect to outdoors? It's a test worth doing if you haven't done so yet.


The upstairs unit has the same problem but to a lesser degree because its returns are on the ceiling as well. It can run for 30 minutes and I know I’m only getting about one third its potential efficiency.

How do you quantify that?


I’ve seen before and after effects of window and door replacement, it’s a good part of my business. Have you seen before and after effects of poor return placement? Just because improving thermal envelopes is a very legitimate fix doesn’t mean it negates other contributing factors in indoor discomfort.

I've been in homes with ceiling returns and homes with floor returns. Ceiling returns often indicate HVAC equipment and ducts in the attic, which is just about the dumbest thing possible to do with these systems. HVAC in attic = capacity loss. HVAC systems that perform the worst in my climate, even when charged correctly and clean, are attic mounted systems. Unless the attic stays cool in summer and warm in winter, it is robbing capacity from the HVAC. Ruh roh...we're back to envelope discussion again! Dang it. :)



Put the return downstairs so it pulls air down the stairway instead of up it.

I agree your particular return air provision for the downstairs should be downstairs. So should the rest of the equipment for the downstairs! As it is, whenever your downstairs system runs, it pressurizes the downstairs rooms, leaving no place for displaced air to go but up the stairs, where a negative pressure exists due to the returns.


The rising heat problem of the two story house would be at least minimized when the unit is on. This would at least allow the house to heat. The worst case I saw was while I was crowning a newly remodeled two story house with new windows, doors, insulation, and heating unit. I watched the unit run for an hour, trying to heat the house, but the large single return at the top of the stairway made the accumulation of heat impossible. The house never heated. I felt sorry for the poor homeowner who just paid for the job.

How cold was this house prior to the system kicking on?


I wouldn’t. My point was that a poorly designed heating system is not overcompensated by a tight envelope. A poorly designed system is a poorly designed system, regardless of the envelope.

This can't go by without comment, since it's a blanket statement. An airtight house will compensate for poor duct system design. It's no cure, but you can't say with certainty that if you take a house that leaks like Swiss cheese and tighten it up, but do nothing about the ducts, there's no measurable difference between the two states. In some cases there may not be, but it demands to be quantified/measured, not just surmised about.


You know removing the unwanted water first is the correct approach, but you don’t want to say it because you may think it lends credence to my points. I know it isn’t’ directly applicable, but the similarity is close enough.

Your illustration painted in my mind a container undergoing water circulation. Withdraw it, pump it, return it. If the sediment has settled at the bottom, and you draw from and discharge to the top, the sediment at the bottom may or may not stir, depending on the rate of circulation. My experience with pools is that if there's sediment on the bottom, you get the plaster vacuum head and slowly move it across the bottom, so the concentrated low pressure zone created by the hose attached to the skimmer does not stir up the sediment before it can be removed.

But we're not talking about water and sediment, which brings into the picture matters of filtration when comparing the illustration to air movement. We're speaking of a fluid, yes, but a gaseous one, not a liquid. This fluid's entire point of reference is human comfort, not sediment suspended in liquid. Have you ever noticed how we like water to be warmer than air before we swim or bathe in it?

[Carnak]

Carnak,
If you are attempting to invoke a response out of me you can hang it up, I won’t.

Though you may be very good at HVAC in general, I still consider you to be too rude, adversarial, and incomprehensive of the English language to waste my time with. But maybe your fan club gets a kick out of your antics, so carry on.

Brian, I think you are out of your element and should be grateful for the advice you receive here.

I would get frustrated too if every barnyard analogy I proposed was shot down with cold hard fact.

You are confrontational and cry like a little girl when you receive a fraction of the attitude you give.

You should have watched the video link in the post that got your panties in a knot. A guy in Canada with a tight well insulated home was able to keep his place comfortable for a week without power in the winter utilizing a gas fire place. No power no forced air, so build a tight insulated place and a pot belly stove will keep it comfortable.-- that has to be the worst heat distribution there is, no ducts.

[Carnak]

maybe try sleeping at a Holiday Inn