[beenthere]

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.

 

[davo]

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.

 

[Skip 2 my lou]

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.

 

[beenthere]

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.

 

[davo]

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.

As I said in the beginning of the first post, proper air return is vital to comfort and proper operation.

I have had many contractors try and solve poor thermostat location problems with returns to no avail.
If the thermostat cannot sense the load, how can it keep a separate room with a lot of load comfortable?

 

[beenthere]

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.

 

[pstu]

Got a nagging problem with our 5-ton Trane setup. It's a 3-zone system on an older split-level (three levels) cedar shake house. 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. My husband tells me that the only way to fix this is to install grills/vents in all the doors, but I'm thinking there has to be another way. After all, new homes don't have all the bedroom doors vented. I don't want the kids hearing what goes on outside the bedroom, nor do I want them to hear what goes on inside the bedroom. Are there any other options? Thanks very much.

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

 

[bhe]

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

 

[beenthere]

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.

 

[21degrees]

Thermostats will sense collective air.

You are totally right if you close all the doors and are only sensing interior air. But if you just close 1 door it should not create problem. Return airs in rooms with doors closed and no room under door to allow pressure equallization will be problematic and will not heat or cool properly. Air flow is way to important. Just as you need supply air you also need return air.

 

[davo]

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.

 

[bhe]

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]

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.

 

[BigJon3475]

Probably to late:

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

 

[bhe]

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.

 

[m kilgore]

As Mr Bill said I would make sure that there is a bypass for the zone system. If not it will cause allkinds of problems as you have described. This would be a jumper duct with a damper between your supply and return by your furnace. With zoning it is critical to have the duct done right and the by-pass put in unless there is a variable speed furnace and the manufacturer has a system to tie in with the zones.