Basement HT -- HVAC + Soundproofing

[varneyb]

My HT is going in our basement, and for a variety of reasons, we decided not to go with room-within-a-room construction. As a result, the drywall for the HT will be screwed directly to the joists above. However, I have 3 return air ducts comprised of sheet metal nailed to the bottom of the joists (one for 2nd floor, one for 1st floor, one for basement). Sound is going to go right through these. On the end of each "chase" is a piece of 1" fiberglass "duct board" (the kind with the silver on one side).

I was thinking of taking the sheet metal down, and using the same duct board in it's place. Instead of being attached to the bottom of the joist, it would fit up in the joist (flush), and I would seal it off with caulk and silver tape. Does this sound sensible?

In addition, I'm thinking about HVAC concerns in the room. I have a zoned system, which treats the entire basement as a single zone (3 zones - one on each floor). The basement will also have an office, family room, and kithenette. The HT area has one vent, and one air return. There is also a vent in the kithenette, one the the family room, and one in the office (but no other air returns). The thermostat for the basement zone is in the office.

Should I add another air return? Should I move the thermostat into the HT?


Thanks for any help,
Bruce

[dwightrahl]

Replacing the sheet metal with ductboard sounds like a good idea. It will eliminate any potential "ringing" effect, but you will likely still have some sound transmission from the HT to the room above. Soundproofing is an extremely difficult thing to achieve - about the best you can hope for (IMHO) is to reduce the amount of sound transmitted; you'll never eliminate it all.

As far as the supply-to-return ratio is concerned - you really should have a pro evaluate your situation. Getting the correct balance between supply size, return size, air velocity, etc, gets to be pretty complicated pretty quickly. And then, of course, there are the issues of balance between the different zones. Fouling up these issues can lead to a lack of comfort throughout your home, and can also cause premature failure of your heating/cooling equipment.

It's been my experience that most homes are lacking in return air duct sizing (based on my own home, and that of a neighbor's who just had an addition added - both pro's that we used commented about the lack of proper return air capacity in most homes). In my case, I added a HT, an office, and a playroom in the basement; each with a single supply and a single return. The three additional retutns brought the static pressure of my ductwork into line with what it should have been originally.

Make sure that the pro you hire has experience in residential zoning applications, and check his/her references to verify that they know what they are doing! Zoning an air system is not a simple thing to get right.

Good luck and let us know how you make out.

Dwight

[sharerware]

Bruce,

How did you end up attaching the ductboard to the joists???

Mike

[uxbridge]

I was thinking of taking the sheet metal down, and using the same duct board in it's place. Instead of being attached to the bottom of the joist, it would fit up in the joist (flush), and I would seal it off with caulk and silver tape. Does this sound sensible?


Be careful that you don't choke the return, with too thick of ductboard.

Should I add another air return? Should I move the thermostat into the HT?

You need to to do a heat loss/heat gain calculation to determine how much air you will need? Will your A/C need to run in the winter for the HT?