My HVAC contractor seems to think that an unlined return air plenum is an acceptable answer. The return he installed will depend on the drywall forming a perfect seal with the framing to keep from pulling air out of the unconditioned attic.
I am not a happy camper.
Rather than expecting the obviously clueless installer to come back and do something that will actually work, I am going to fix it myself.
Does anybody know off the top of their heads what materials are code legal for lining a return air chase?
Replies
You don't need to line it, you just need to seal it.
The way they have cut up the framing to install the return vents means that I would have to seal around the chase and two adjacent wall cavities.The return ducts will obviously be moved, but I do not see a reliable way of sealing the chase without lining it. I don't think that relying on the dry wall installers to make it air tight is going to work and trying to seal it up after they are done isn't that simple either.At the moment, I am leaning towards using dry wall to line the interior of the chase.
Paul,
The practice of using framing cavities as part of a forced-air duct system is not only bad practice, it is a code violation in most jurisdictions. For example, Section 403.2.2 of the 2004 IECC requires that “All ducts, air handlers, filter boxes, and building cavities used as ducts shall be sealed. Joints and seams shall comply with Section M1601.3.1 of the International Residential Code.” Section M1601.3.1 of the 2000 IRC requires that “Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems.”
Framing cavities are not "sealed," nor are they "substantially airtight." Your installed must use ductwork, with seals sealed with mastic or approved tape.
But this is return air ductwork. Are you sure the quoted text applies in that case?
If your view never changes you're following the wrong leader
Dan,
Yes, return-air ductwork is part of a forced-air distribution system. It is essential that return-air ductwork be installed in a manner that is as leakproof as possible. Otherwise, a pressure imbalance can occur between the supply air distribution system and the return air system; such an imbalance can result in pressure imbalances between rooms in the house, and can cause exterior air to be drawn into the forced-air distribution ductwork.
Possible problems from such pressure imbalances include high energy bills, humidity problems, mold problems, and comfort complaints due to poorly conditioned rooms.
You're assuming that you have a return in every room with a register. That's not the norm.
If your view never changes you're following the wrong leader
DanH,
I'm not assuming there is a return in every room, although if there is, it is a very well designed system. If the house lacks a return in every room, some method of pressure balancing is essential. Undercutting the door is rarely adequate, so the best solution is a jump duct between any room with a door and a common room or hallway where the return is located.
I an assure you that if the system lacks a return in every room, and if jump ducts are not provided, there will be pressure imbalances (and attendant problems).
we just use green board and tape the seam with the silver tape.Know BOB, Know Peace
Yeah, there will be pressure imbalances, but we don't have any attendants, therefore no problems with them.
If your view never changes you're following the wrong leader
The city of Fort Worth uses the 2003 IRC. Looking at the applicable text in that, and at the work the installer did, an inspector 'might' pass it. The code for the return air duct is a lot more lenient than for the supply duct.Whether he would pass it or not, I didn't. I spent a few hours with drywall today and have it fairly well complete. I tried to find some duct board, but couldn't find an open supply house on a Saturday.
Well, you only need to seal the top edges, which is a good thing to do in any event. In our house I poured "elastomeric" roof coating (a rubbery gunk)) over the tops of the studwalls to make sure they were sealed.
If your view never changes you're following the wrong leader
We see this done a lot in highrise condo's we build. As the framing/ drywallers we always supply a disclaimer for any moisture, fire, draft issues that might occur.
This is done often and I believe the archies are incorrect in calling them plenums, which in industrial situations are always rated assemblies.
Mike
Trust in God, but row away from the rocks.
We do a lot of weatherizing for the utilities in Texas.
I notice your from FT Worth. If your house is at least three years old and you have an Oncor meter you can get a weatherizer (like us) to do it for free provided you are all electric. Email me if you are interested.
If it is new or you just want to do it yourself drywall, mastic, and mesh tape should satisfy or exeed any code in your area. We have used this technique in FT Worth with never a problem.
Where there's a will, there are 500 relatives