Instead of putting vents in the doors you can have your hubby undercut the doors a 1" or so off the bottoms of the doors will serve the same purpose as putting vents in the door's. By doing this will allow the air to move out of the bedroom when the door is closed and not get too hot or cold.

 

Thanks, DanW13. I appreciate your reply, but to me, that's about the same as putting a vent in the door insofar as hearing what goes on in/out of the bedrooms is concerned. I'm really curious about what new construction homes do if they don't have the doors vented or cut too high off the floor. Guess I'm hoping that some cool stuff can be done with thermostats or something like that.....

 

r a problem

New construction that i've seen have a return in every room , except kit & bath of course , can u use joist spaces for returns at all????.......Jack

 

"Jumper returns" can be installed from the ceing of the affected room to the hallway or living area.


Undercutting the door 1" would give you almost 30"s of free area ,with no grille restriction and less sound transmission then grilles in the door.

 

Done right. jumper ducts won't tranmit sound like an under cut door.

 

Thanks, rojacman, been there and dash.
There is a return air in two of the bedrooms, but I'm sure that's not the same as a jumper duct. That sounds intriguing. We have joist or attic space available for all three bedrooms in question. Can anyone give me a little more detail on what a jumper duct is so I won't sound like the newbie I am when contacting an A/C professional? The guy who installed ours would only tell us to install vents in the doors, and I just thought there had to be other options. Thanks again.

 

Do those 2 bedrooms also have trouble cooling when the doors are closed?
If so, the returns may be undersized.

A jumper duct. Is when you install a register in the room, and then run a duct out to(in your case) the hallway. And attach it to either a register cut into the hallway, or into the return box in the ceiling above the hall.
If the return in the hall has a filter in it, then your need to install return fiter grilles in the bedrooms.

 

A little while back I found this on building science and it talks about transfer grills

"Transfer Grille
From Builder’s Guide, Building Science Corporation
• All supply registers should have clear access to a return grille in order to prevent the pressurization
of bedrooms and depressurization of the common area. Bedrooms should either have hard-ducted
returns, or another means of pressure relief, such as transfer grilles (above) or jump ducts (below).
• Maximum that can be returned by through-the-wall hi-low transfer grille is ~125 CFM, assuming
door undercut.
• Door undercut of 1” minimum still required
• Pressurization is especially severe when combining oversized air handlers (e.g., 5 tons in 2000 sf)
and large master bedroom suites that can be sealed from the main space with one door.
Undercutting the door seldom provides adequate pressure relief.
• Refer to Transfer Grille Sizing Table to compute required free area (and grille size) vs. supply airflow."



I tried loading it up again and for some reason the doc. won't load up now it maybe my laptop.....it showed all the different types that these guys are talking about.

 

Wow, BigJon3475 - your post hit the problem right on the head. The bedroom I have the most experience with has a major problem with pressurization. When the A/C turns on, the door will close by itself if it's just a little ajar. And I believe we have too large of a unit - it's 5 tons for 2100 sq ft, 3 zones. (The force of the air upstairs, closest to the air handler, is incredible and I think we were misled into thinking we needed the larger unit, but that's another issue entirely). I found a website for buildingscience.com, is that where you got your info?

Beenthere, yes, those bedrooms have trouble cooling when the doors are closed. You have to turn the thermostat down at least 3 degrees for that room to be as cool as the living area when the door is closed, and the living area then gets too cold, of course. The return air on the main bedroom, with the pressurizatino problem, is not too small - it's about 10X20.

Thanks SO much.

 

Beenthere, yes, those bedrooms have trouble cooling when the doors are closed. You have to turn the thermostat down at least 3 degrees for that room to be as cool as the living area when the door is closed, and the living area then gets too cold, of course. The return air on the main bedroom, with the pressurization problem, is not too small - it's about 10X20.

Thanks SO much.

The grille may be 10 x 20, but what size is the duct thats hooked to it.
In order for that room to pressurize, the supplies must be putting more air into the room then the return can take out.

 

Building Science Corporation


http://www.google.com/search?hl=en&q=building+science+door+undercut&btnG=Google+Search



See if you can view it I can't.

 

No go, Big Jon3475. I tried just looking for the Builder's Guide, but the links were to a place to purchase the Guide, not for info in the Guide.

I guess I just need to find a good A/C technician. Unfortunately, the last one (that installed this system and it's ductwork) doesn't seem to know all there is to know, and referral from a layman is probably not going to be helpful. After all, our guy was really nice and honest and hard-working, but this issue requires more technical expertise than he had, apparently. Got a clue about how to find someone really knowledgeable?

Thanks again.

 

Try this;

http://www.buildingscience.com/bsc/designsthatwork/hothumid/profiles/montgomery.htm

 

If you have a zoned system you should have some sort of Barometric Pressure Relief Bypass Duct, if not you sure will be having issues with Pressurization in some rooms, unless you maybe have a dedicated return for all rooms, if your in a pretty humid area you could also get your tech to look at slowing down the CFM's to 350 per ton., or is this a VS air handler? not much was mentioned about equipment except it was a Trane system.

 

Thanks, Mr. Bill. Unfortunately, I'm just a layman and have no clue what a VS air handler is. I'm in Jacksonville, Florida, about as humid as you can get. Pressurization isn't the main problem, of course, I guess it's a side effect of what's causing the problem, if I'm understanding everyone correctly. What a helpful bunch of people you are.

 

Thanks, Mr. Bill. Unfortunately, I'm just a layman and have no clue what a VS air handler is.

"variable speed" That means that the Air handler has a variable speed motor in it, most of these motors are able to overcome a lot of air duct issues that other fixed speed motors can't, by ramping up or down when needed, hope this helps.

 

Thanks, dash and Mr. Bill. This is good information. Perhaps I can do a little more research on this and then (hopefully) find a good A/C guy that understands this stuff and can apply it to our situation. Any certifications or something like that to look for when trying to find someone?

 

Please do a simple experiment before you have more grills and jumpers cut in, although proper air return and pressure equalization is essential to good operation.

You see, you are not saying the rooms don't cool, just the hallway and living areas are cooler when the bedrooms are at their desired temperatures.

Prop the doors in question open from the door frame the width of a shoe.

Let them run for a day or so. If that solves your problem, jumpers and such may help.

If the rooms are still hot, it may be a simple thermostat location issue.

In new homes, and especially Master bedrooms, windows are prevalent. If the bedrooms rooms faces north east to northwest, a thermostat in the hall may not trigger on....especially with the doors closed. Hallways are generally toward the interior of the home, and bedrooms generally on the outer part of the home with external walls and windows. I find many times air from the other zones keep the thermostat off and satisfy it early. The living area part of the zone in question, may be getting help staying cool from other zones.

Zone systems should try to be set up where similar loads are grouped together so this does not happen.
Once the thermostat can sense the load properly, airflow can be balanced.

 

You see, you are not saying the rooms don't cool, just the hallway and living areas are cooler when the bedrooms are at their desired temperatures.

From the original post.
The thermostats are all in a hall area, which seemed like a good idea at the time of install. However, what happens is that when a bedroom door is closed, it'll get too hot because the thermostat is not in that room.

She also said that they get cool if the door is left open.

 

move the thermostat to the bedroom

 

Yes she did, but with the doors open, sometimes the natural movement of air will allow the t-stat to pick up the heat.

With the doors closed, there is no natural air movement.

 

And since at least one room is pressurizing when the door closes, its a lack of return for at least that room.
Good chance if one bedroom is low on return, the others are also.

 

With the system on and the door closed ( standing outside of the door, ) place your hand at the bottom of the door. If you have a strong flow of air coming from that gap, under the door, you more than likely need a return in that room. There is a good chance that you are supplying a large amount of air to the room and it is having problems getting back to the system.

If that is the case, your hot room is affecting the performance of the entire system.

Undercut the door to increase the gap or add a return inside the bedroom.

 

Not many houses have a thermostat in the bedroom. But many of them are keeping the bedrooms comfortable, without sensing the actual load in those bedrooms.

If those bedrooms are getting the air flow they need(supply and return) they will heat or cool at the same rate as the rest of the house. A person sleeping doesn't add that much heat to the room to make it gain heat that much faster then the stat location to count.

Once the sun is down, there is no solar gain to make a bedroom a higher load then the stat location.

 

Everything from Building Science Corporation is excellent, but here is another good report on the same problem:
http://www.tamtech.com/PDF/R.A.P. Article. SoFL. 08.02.pdf

This is a corporate report designed to support sales of a commercial product:
http://www.tamtech.com/rap.htm

Just wanted to show another alternative that looks valid to me, a homeowner in S.Texas. But if there is already a return in the bedroom, I would first look into whether the problem could be solved by a larger duct to that return. With the advice and consent of a pro who understands airflow of course.

Hope this helps -- Pstu

 

Wow! Thank you so very much, all of you, in trying to solve my problem. I really, really appreciate you taking the time out to help me.

I checked last night, and all three of the bedrooms in question have air returns. Two small - 10x10, and one larger 10x20. The one with the larger return has the pressurization problem; although I haven't put my hand by the bottom of the door to actually feel the airflow, having the door actually pull itself closed when the A/C turns on seems like a confirmation of that problem. Funny, the bedrooms with the smaller returns don't have that problem, although the A/C just blows you away when it's on - it's way too strong. I have no clue about the size of the duct; I'll have to check the attic this evening.

The thermostat for the room with the larger return is in the living room, (which faces West and has a huge picture window), under one zone, and the thermostat upstairs for the two other bedrooms is in the hall, under another zone. The hall thermostat is right by the stairs, so I know that it's getting air from downstairs, which exacerbates the problem.

I feel that the location of the thermostats may be the main cause of the problem, but if we move it to the bedroom, won't that just move the problem from the bedroom to the living room? Same thing upstairs - if we move it to one of the bedrooms, the other bedroom will have a problem, especially since one bedroom faces East and the other faces west, with large windows.

So, like davo wrote, was my contractor trying to solve the problem by putting returns in every room, but ended up making it worse because of the location of the thermostats? He didn't have any recommendations about where to put them.

Pstu - thanks for the link. I had no clue that a pressurization problem could lead to mold. The Building Science info mentioned that, but it was pretty technical and I didn't quite "get it". Luckily, we have no vinyl wallpaper, but still..... The product from Tamarack Technologies looks like something we need to look into. I especially liked the baffle to eliminate sound transfer, and the notion that only a 1" undercut, combined with the jumper ducts, will make a large difference.

Does everyone else agree this is the best way, or should we move the thermostat(s)?

I just thought of something else. We had new, high-end, windows installed last year, triple-pane with argon gas and Energy Star certified. They replaced 1952 super-leaky aluminum casement windows. They're a great sound barrier and I was also expecting a lower electricity bill, but there was absolutely no difference. Wonder if the inefficiency of the HVAC system is the reason......

Thanks a lot.
Bettina

 

If you move the stat to one of the bedrooms. You will have the reverse at night time. But then no one will be in the other area to notice it. And aslo as teh doors are open during the day, the other area may be ok.

 

Let me reiterate, I never said returns were not required. I said it may not and probably is not her problem.

In Florida, many many zoned homes, have thermostats in the bedrooms.

I have a sensor in every single room, and even one in the master bathroom.

A door closing when the a/c turns on does not always mean the return is too small, although it could be a possibility. The room has to pressurize a little to cause displacement for the return to move air. It does not take to much to move a bedroom door.

My master bedroom has a 14" return with a 18"x 18" RHF type grill. More then large enough. My return static berfore my Infinity Air Purifier is .03 at full speed, 3 tons There is also a wall releif system I have not closed off yet.
My door closed when the zone calls and the door is left open about 2"-3".
Maybe I should add more returns? Could it be the unit is mainly drawing from all the closer returns, and a little pressure differential is needed to cause flow?

Remember, returns don't suck, air moves through them due to displacement.

When zoning, it is important to try and group areas with similar exposures and loads together to avoid this problem.

Adding returns will not hurt, but it probably will not solve the problem either.

Once the system is triggering on and off properly, air balancing becomes much easier.

Your house, your money, your comfort.

 

Davo, what is a sensor and how would it affect the thermostat / cycling on/off of the unit?

Regarding the return where the door closes when the A/C turns on: It just happens to be right next to the door, which is in a little alcove area, not in the main room. Perhaps the location is the problem.....?

Bettina

 

Davo, what is a sensor and how would it affect the thermostat / cycling on/off of the unit?

Regarding the return where the door closes when the A/C turns on: It just happens to be right next to the door, which is in a little alcove area, not in the main room. Perhaps the location is the problem.....?




Bettina

Remember, none of us can "see" your problem because we are not there.

You said you have a large return in this room. We don't know the duct size to the return. Depending on the size and length of the return duct, and the size of all the other return ducts on the system, the room is probably just pressurizing a very small amount before air flow starts through the return.


In my home I have a fancy system that uses remoter room sensors instead of thermostats. They basically do the same thing, sense temperature.

 

Probably to late:

[FONT=Arial,sans-serif]The Building Science Corporation.[/FONT]

 

Thank you, BigJon3475. It's not too late - I got some other info, but this one is more detailed and easier too understand.

What I plan to do is (try to) find an A/C guy that is more up to speed on this kind of thing. Do you know if there are any certifications or anything like that I should look for? I just hate to start from scratch in the Yellow Pages. The guy that installed our system came recommended, and he was very nice and very honest, but apparently he's not too experienced with our kind of issue.