Door transfer grilles

greenjp

Good morning everybody,
My house has three bedrooms on the third floor, a master with 4 supplies and two small kids rooms with 1 supply each. There's a single large return in the hall between the rooms. The supplies in the kids rooms are shut about 3/4 of the way, when wide open they got way to much air and the rooms would be much cooler/hotter than the master. When the AC or heat is running all the doors get sucked shut.
The undercuts are only ~1/4", so I'm thinking of putting in some door transfer grilles. There seem to be a lot of companies who make them but most distribute only through commercial-type suppliers. Atlanta Supply has some available (apparently) but I'm having trouble sourcing aside from them. I thought perhaps the contractor who recently replaced our HVAC system might do me a solid and order them for me?
I have a differential pressure gauge which I'm planning to use to check the pressure delta with the doors shut to get a feel for what the right size would be. I'm restricted by the size of the flat part at the bottom of the doors though.
Any thoughts or tips? Thanks,

jeff

beenthere

Don't use door transfer grilles on bedroom doors if you want any privacy in those rooms. Use either jumper ducts in the ceiling, or install a grille low on the bedroom wall, and then high on the hallway wall, to minimize sound transfer.

bobinphx

we added transfer grills to the kids bedrooms in our house. What a difference they made!!!!

we were lucky as there is a jack and jill bathroom that has a common wall with the hallway near the return. The transfer ducts were used from the rooms, to under the vanity and then out to the hall. The hard part was sealing everything so that no air would leak out to the floor joists and or wall cavity. But, again, what a huge difference they made!!!!

greenjp

Thanks for the input. I did some experimenting today and found a few things:
The kids' rooms doors don't get sucked shut nearly as forcefully as the master bedroom. In fact I probably overestimated how strong it was on those. The undercut on those doors is less than 1/4". The rooms are ~ 100 square feet with just the single, partially closed supply.
The master bedroom door will close itself if it's open 6" or less. It'll close all the way and latch. Including the bathroom and closet it's probably closer to 300 square feet and has 4 supplies which are all open.
The differential pressure gauge I brought home from work does not go down to the scale of these measurements.
FYI the attic above these rooms is unconditioned.

So I have a couple of thoughts. For the kids rooms, I'm thinking of just undercutting the doors so there's a 1/2" gap with the carpet.

For the master bedroom, there's enough space either above the door, or from the walk in closet (the door to which is always open) to put a transfer grille out to the hallway. The high-low grilles sound like they'd work for the closet approach but I worry about how well sealed up that space is with the attic right above. The other option is something called a "Return Air Path" made by Tamarack which has a frame to alleviate that leakage concern and an insert purported to attenuate sound. Thoughts?

jeff

Doc Holliday

Or simply add a return in the master.

__________________
Thanks.

bobinphx

at the same time we added the transfer grills, we also added a second return (18 inch steel duct, 25 by 30 grill). This was the best thing we ever did. The original return was very undersized (25 by 30 for 5 ton heatpump)

We could not add returns in each room, due to obstructions in the attic, but I sure would have if I could.

each situation is different, but if you have the room and you seal and insulate correctly, a return in each room is not a bad idea!!!!

Gissle

I live in the UK and the firm I work for has a wing that sells transfer grilles. We would sell to anyone and you can pay over the phone.

However, over here you can buy cheap transfer grilles in DIY stores.

I hope this helps.