Rooms with doors closed too hot or cold
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.
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.....
"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.
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
Originally Posted by bhe
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
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 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.
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?
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.
Last edited by Mr Bill; 06-09-2008 at 06:13 PM.
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