Home>Discussions>INSULATION & HVAC>Sealing ductwork - Specifically the return system in the joists
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WINT142000
Sealing ductwork - Specifically the return system in the joists

Our return duct work has some serious air leaks and is not 'pulling' air out of the far reaches of the system. The basement is unfinished and when the system runs, it is pulling air under and around the door leading to the basement versus through the HVAC system. I am planning on sealing up the ducts, but one are I am not sure how to best tackle is where the return vents head up from the joists. Sections of metal were added in the joists and then the I-beams were blocked with chunks of wood and there are some pretty significant gaps. I do not know what I can use to best seal these. Would mastic work? Caulk might work, but some of the gaps are pretty large. Any advice would be great! See photos for a few examples.

Thank you!!!!

http://s1294.photobucket.com/user/wint142000/media/House%20items/DSC09348_zps1ba5f907.jpg.html

Mastercarpentry
Re: Sealing ductwork - Specifically the return system in the joists

Mastic should seal these but the whole thing seems like a bodge. The ducting should go through as a whole, not being connected to wood on either side with the wood forming a part of the actual ductwork.

I'd call in a HVAC contractor to inspect the whole system and follow their recommendations- if they took shortcuts here they are sure to have done the same elsewhere so the entire system is now suspect. You may also want to have a engineer or contractor check the structural integrity too. You're not supposed to go through IJT's like appears to have been done here either.

Phil

WINT142000
Re: Sealing ductwork - Specifically the return system in the joists

I was under the impression that forced heat had to be in runs, but returns could be between joists. Not positive on this though...

Mastercarpentry
Re: Sealing ductwork - Specifically the return system in the joists

Perhaps it is allowed by code, but is it a good idea? Wood is permeable, so any odors which get into the return may get into the wood and stay there, recirculating out the forced air downstream. Also wood is organic which can allow organic things like mold and mildew to grow on them more easily than metal. And worst case scenario, if fire gets drawn into a wood return duct it my not be obvious and restart where you thought it was out. Metal has at least some resistance there.

Just because you can do something does not always make it a good idea to do it that way!

Phil

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