Whacko Designed System

[coolinhouston]

About two years ago, I bought a custom home as a builder's foreclosure. Great buy, but obviously some unknowns in it. My first great surprise was that it was plumbed to run two 40 gallon gas water heaters and two furnaces from a 3/4" gas line. That's now been replaced with the 1.5" line.

The home is a three story town house with a total square footage of 3860. I'm currently running a 4 ton and a 5 ton unit. Unfortunately, and I'm almost certain that it has undersized ducting to most of the rooms. For instance, the master bedroom has one 6" duct for a room that is 14' x 17'. About half of the rooms have similar duct sizing issues. Of course, if this were a one story and all was coming in from the attic, reducting would be a reasonable approach. But it's three stories. Of the contractors I've spoken with, one suggested reducting, which was going to be a lot of expense and misery for a long time during construction. The other suggested a larger blower motor, I assume to force more air through the system along with some type of a valve on certain ducts to turn them down where they didn't need it.

My fear is that with a larger blower motor that it would also create noise of air rushing through the ducts, especially if one were closed a bit with the valve. Is this correct? Any other options?

The other odd thing is that the 4 ton until supplies the first two levels of the house, which are mostly open to one another. There is a second story loft area that opens to the first floor. The 5 ton unit is supply just the top level, which is basically 1/3 of the square footage and more isolated than the first two floors (only a stair case leading up to that floor). Given the under plummed gas line (which I still can't understand how it passed inspection), I'm fearful that the two units are actually reversed - the 5 ton should be for the first two floors and the 4 ton for the third floor. Is this a valid assumption? Is the fix to this as simple as rotating the equipment?

Thanks in advance!

[Shophound]

What I did not see in your post above is where you may be having comfort problems in the townhouse. I assume you are, hence the motivation for your post. Tha said, it helps us to know how you're uncomfortable; i.e. rooms too hot, too cold, too humid, too stuffy, etc.

Townhouses can present several challenges toward keeping the interior spaces comfortable, some of which you touched on above. The ultimate solution may not be just HVAC based, but also an evaluation of how the building is constructed to better understand how to tackle the problems you face. I suggest an energy audit with a focus on finding problems with the building's insulation, air leakage, thermal bypasses, etc. You may find that by tackling the building issues first, the HVAC isn't the only source of your problems.

[tedkidd]

Are you having problems cooling?

Have you done a load calculation?

Sounds like you have system/duct mismatch. 9 tons sounds a b s u r d, so the duct may not be the bastard child here. But what problem are you trying to cure? Please don't make us guess what problems you are trying to fix. Be specific if you want meaningful advice.

People have endless problems, it's the ones they actually perceive worth addressing that matter.

[Tommy knocker]

You have plenty of tonnage that's for sure. 428 sqft per ton is alot of cooling. Looks like about 250 sqft per ton on top floor. Alot of red flags in your post. Gas line, equipment sizing, equipment placement, air distribution etc. I would suspect short cycling of equipment, over cooling, insufficient dehumidification, hot and cold areas, just off the top of my head. If the info you posted is correct you got lots of issues. Find a reputable contractor to come out and evaluate. Sounds like someone's cousin's nephew's friend's brother in law knew a guy that changed a filter once so they hired him to design build this system. Good luck.

[coolinhouston]

Sorry, I only described how the system was set up. Here are some more details and specific problems:

1) The building is VERY well insulated. All exterior walls have cellular insulation tightly blown in betweent the wall with a stucco exterior. The attic stays cool (big deal in Houston).
2) The weather stripping around all of the doors is solid. I can feel some slightly leaky areas, but that is to be expected with the type of doors typically used in Houston.
3) I generally keep the air at 70 on both units at night and 72 during the day. My average electricity bill at these temperatures is relatively modest for those temperatures, the humidity levels in Houston and the square footage. We do run A/C about 10 months out of the year in Houston and my average is about $200 per month. So there isn't a real problem with efficiency.

Problems that I'm looking to correct have a lot to do with comfort and more efficiency. I'm trying to balance changes on equipment with cost to ensure that I have a monetary ROI and comfort ROI. Per a previous post, I'm looking to change the outside units to something more quiet and compact. I think I have that figured out. But in doing this, I want to evaluate rotating the units and the possibility that a larger blower motor to get better temperature balance, consistent comfort and maybe a little cost efficiency (although I don't expect a lot of operating cost savings).

1) Interesting, at 72, the airconditioners do not run that much during the day. (I work from home, so I see them). But in the evening and at night, they run almost constantly to keep that 2 degree difference.
2) I've adjusted for the imbalance of tonage by keeping the upstairs cooler, earlier than the downstairs. It seems to balance the whole house better. Unfortunately, it's a waste of money because there are only two of us and we don't spend that much time on the top floor.
3) The master bedroom (2nd floor) at night can suddenly turn very warm in the middle of the night. Perplexing, but I suspect that the top floor comes to temperature and shuts off so I don't get that down draft cooling effect. But that doesn't make sense because the thermostat that controls the top floor is right outside the bedroom. Maybe it needs to be moved to where the unit it is connected to is cooling the area - if the unit only cools the 3rd floor, the termostat needs to be on the third floor.
4) As a result of the above, the top floor is like an icebox when we do have guests or are entertaining on the top floor (game room and terrace).

I hope this provides the information that you're looking for.

This is such a helpful forum and I so much appreciate the professionals who contribute to it. Most of the people that come out here to look at things I feel are just trying to sell me equipment and services - not look to optimize what I have. So the advice you guys provide helps me get more resonable with them and challenge their sometimes audacious proposals.

[Tommy knocker]

OK. Keep in mind we are not there and only have information you have provided to draw our conclusions from so do not assume we are rite and the techs on site are wrong or trying to gig you. Please don't take this wrong but you may not understand your system and may be giving us inaccurate information. With the information provided I'm inclined to think your system was designed and put in by 3rd graders. Everything is backwards and poorly sized. But agin I am not there and cannot see it.

[tedkidd]

If you are considering significant investment you definitely should have a comprehensive assessment first. Here are some things that would be nice to know:

- CFM50 leakage of the home.
- Ducts in attic? Duct leakage.
- External Static Pressure of both systems.
- Load calc INCLUDING your cfm leakage, not a WAG (wild ass guess)
- Track cycle time on really hot and really cool days. Not cycle time for recovery, cycle time when recovery is NOT requested.


Other food for thought:

People who complain of equipment not shutting off tend to have noise or comfort issues around equipment running. Oversized and non-modulating equipment are typical causes.

The more efficient your envelope, the less energy replacement (horsepower) needs it will have. Imagine a freight train. That sucker moves a lot of freight CHEAP, but it don't go 0-60 in 5 seconds. There is so much mass, and momentum behind that mass, that changes don't happen quick.

Conversely, you don't get a comfortable and efficient ride in a Ferrari.

So a strategy that jerks temperature around requires a lot of hp, and you won't get low bills.

Also, Imagine a well insulated beer cooler. Does it save a lot of ice to not cool a small space within the cooler? Think of your house as a well insulated cooler.

The way you think of a crappy house is completely different. Strategy for heating a corn crib and strategy for heating a beer cooler are polar opposite.

[jpsmith1cm]

Tommy knocker,

Please check your e-mail.

[classical]

double post

[classical]

Jared I have dealt with numerous homes just like yours here and I can tell you upfront you have more than double the necessary cooling capacity. Your home more than likely needs 3 maybe 4 tons of cooling not 9-tons. The good thing is the ductwork is mostly likely adequate for your needs but not your current equipment.

You need to have an accurate load calculation performed and then a manual D performed to assess the ductwork. It is possible to fix your home but a through evaluation must be performed to accurately answer your questions.

[jtrammel]

Look up classical's profile and shoot him an email, have him come out and let you know your options. I agree with the others, 9 tons sounds grossly oversized for that size of a house

[bmathews]

This is such a helpful forum and I so much appreciate the professionals who contribute to it. Most of the people that come out here to look at things I feel are just trying to sell me equipment and services - not look to optimize what I have. So the advice you guys provide helps me get more resonable with them and challenge their sometimes audacious proposals.

I have no idea what anybody is trying to sell you. Maybe a bag of goods. But the solution to your complaint could very well be different equipment. You sound a little oversized. We also sell services, we are service businesses. What may seem like an audacious proposal to you may be the solution. You have to understand something from our point of view. When we go out to your house and "fix" something or try to fix something. The person paying us thinks that we own that piece of equipment, even if something unrelated to our repair goes out. So we get in the mindset that if you want it fixed, we're gonna give you the solution to your problem, so when we "own" YOUR equipment, we get it fixed. Putting a larger blower is a ridiculous idea IMO. The unit isn't rated for that blower, it has in it what it's rated for. You're asking for more problems. You might look at Infinity zoning by Carrier, which also requires pretty expensive Carrier equipment, but it might be able to compensate for your whacko ductwork as you put it a little better. It may not be the complete solution, but may require less destruction of your humble abode.

[Krzyd]

About two years ago, I bought a custom home as a builder's foreclosure. Great buy, but obviously some unknowns in it. My first great surprise was that it was plumbed to run two 40 gallon gas water heaters and two furnaces from a 3/4" gas line. That's now been replaced with the 1.5" line.

The home is a three story town house with a total square footage of 3860. I'm currently running a 4 ton and a 5 ton unit. Unfortunately, and I'm almost certain that it has undersized ducting to most of the rooms. For instance, the master bedroom has one 6" duct for a room that is 14' x 17'. About half of the rooms have similar duct sizing issues. Of course, if this were a one story and all was coming in from the attic, reducting would be a reasonable approach. But it's three stories. Of the contractors I've spoken with, one suggested reducting, which was going to be a lot of expense and misery for a long time during construction. The other suggested a larger blower motor, I assume to force more air through the system along with some type of a valve on certain ducts to turn them down where they didn't need it.

My fear is that with a larger blower motor that it would also create noise of air rushing through the ducts, especially if one were closed a bit with the valve. Is this correct? Any other options?

The other odd thing is that the 4 ton until supplies the first two levels of the house, which are mostly open to one another. There is a second story loft area that opens to the first floor. The 5 ton unit is supply just the top level, which is basically 1/3 of the square footage and more isolated than the first two floors (only a stair case leading up to that floor). Given the under plummed gas line (which I still can't understand how it passed inspection), I'm fearful that the two units are actually reversed - the 5 ton should be for the first two floors and the 4 ton for the third floor. Is this a valid assumption? Is the fix to this as simple as rotating the equipment?

Thanks in advance!

Please get a load calc done, I agree you are way oversized on equipment, are you sure of the tonnage? Based on your descriptions, it seems you will need some ductwork modification and you will need to replace at least one system. I can't see 5 tons for 1300 sqft unless it's essentially an attic with no insulation. Definitely get a load calc done, do you have blueprints for the home?

[motoguy128]

So the 2 furnaces are next to each other in the basement/lower level? IF so, on simple fix might be to leak-lag the furnaces and tie the ductwork together and add back draft dampers. I suspect one furnace and the 5 ton AC can carry the whole building. I think one pro on here once said they've never seen a undersized furnace. You'd have to be massively undersized not a ocarry a space over a 24 hour period.

One thing to remember, the larger the home, comparatively more thermal mass and less surface area to volume ratio. Also being 3 stories, you have a proportionally smaller roof as well compare ot a signle or 2 story home. A 4000 sqft home will never use nearly twice the heating and cooling as a similarly designed 2000 sqft home, and far less than 4X a 1000sqft home. A typcial 1600sqft home might onl need 2 tons and 50k BTU's, while 4 tons and 100k BTU's can carry many 4000 sqft homes.

[Shophound]

Sorry, I only described how the system was set up. Here are some more details and specific problems:

1) The building is VERY well insulated. All exterior walls have cellular insulation tightly blown in betweent the wall with a stucco exterior. The attic stays cool (big deal in Houston).

Does it stay cool because the roof deck is insulated, or a radiant barrier is on the roof decking, or you have reflective roofing? Is the roof shaded all day long?

2) The weather stripping around all of the doors is solid. I can feel some slightly leaky areas, but that is to be expected with the type of doors typically used in Houston.

Houston is like Dallas/Fort Worth...soil shifts and doors once plumb can go out of alignment, causing gaps to show up in weatherstripping.

3) I generally keep the air at 70 on both units at night and 72 during the day. My average electricity bill at these temperatures is relatively modest for those temperatures, the humidity levels in Houston and the square footage. We do run A/C about 10 months out of the year in Houston and my average is about $200 per month. So there isn't a real problem with efficiency.

Are you running the a/c that cold to keep the humidity controlled? If so, this can be a symptom of an oversized system.

Problems that I'm looking to correct have a lot to do with comfort and more efficiency. I'm trying to balance changes on equipment with cost to ensure that I have a monetary ROI and comfort ROI. Per a previous post, I'm looking to change the outside units to something more quiet and compact. I think I have that figured out. But in doing this, I want to evaluate rotating the units and the possibility that a larger blower motor to get better temperature balance, consistent comfort and maybe a little cost efficiency (although I don't expect a lot of operating cost savings).

As other pro members here have already said, start with a heat gain/heat loss calculation for your structure. You may need to pay someone to do this if you want the calc done apart from equipment sales. Either that or you can pay a modest fee for HVAC-Calc available here on this site and do the calculation yourself. Either way, it is important to get good data into any calculation performed.

1) Interesting, at 72, the airconditioners do not run that much during the day. (I work from home, so I see them). But in the evening and at night, they run almost constantly to keep that 2 degree difference.

This is due to thermal lag. Sun beats on the building all day long, as well as the air surrounding the building warms up all day long. It takes awhile for that heat to work its way inside. By the time it really gets going the sun is setting or has set, and the air outdoors is still hot. The building interior, being cooler than outdoors, will attract heat well into the night until nighttime conditions cool down. This is called "thermal flywheel"...toward morning, if it is cooler outdoors than inside, heat flow reverses and treks through the building shell to the great outdoors.

Also, when your thermostat bumps the setpoint up to 72, you delay your a/c coming on to counteract heat gain occurring as the day wears on. Had you left it at 70 you would notice the systems coming on sooner and running more often all day long.


2) I've adjusted for the imbalance of tonage by keeping the upstairs cooler, earlier than the downstairs. It seems to balance the whole house better. Unfortunately, it's a waste of money because there are only two of us and we don't spend that much time on the top floor.

Do you have pull-down stairs that go into the attic? Is the attic ventilated? If so, you should consider insulating and weatherstripping the attic access hatch. A product like "Attic Tent" is made for this scenario.

3) The master bedroom (2nd floor) at night can suddenly turn very warm in the middle of the night. Perplexing, but I suspect that the top floor comes to temperature and shuts off so I don't get that down draft cooling effect. But that doesn't make sense because the thermostat that controls the top floor is right outside the bedroom. Maybe it needs to be moved to where the unit it is connected to is cooling the area - if the unit only cools the 3rd floor, the termostat needs to be on the third floor.

Are you saying you depend on the third floor system running to keep your second floor master bedroom comfortable at night? And this third floor system is not connected to your second floor master bedroom?

To Motoguy...Houston residential construction is typically slab-on-grade, so there is no basement. OP's systems are either in a closet or in his attic.

[tedkidd]

1) Interesting, at 72, the airconditioners do not run that much during the day. (I work from home, so I see them). But in the evening and at night, they run almost constantly to keep that 2 degree difference.

This is due to thermal lag. Sun beats on the building all day long, as well as the air surrounding the building warms up all day long. It takes awhile for that heat to work its way inside. By the time it really gets going the sun is setting or has set, and the air outdoors is still hot. The building interior, being cooler than outdoors, will attract heat well into the night until nighttime conditions cool down. This is called "thermal flywheel"...toward morning, if it is cooler outdoors than inside, heat flow reverses and treks through the building shell to the great outdoors.

Also, when your thermostat bumps the setpoint up to 72, you delay your a/c coming on to counteract heat gain occurring as the day wears on. Had you left it at 70 you would notice the systems coming on sooner and running more often all day long.

Nicely explained.

DO NOT ABANDON SETBACK STRATEGY or you are likely to have some real latent problems. You probably really need the long pulls.