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Advice on moving and/or soundproofing HVAC trunks

1940 Views 5 Replies 3 Participants Last post by  DeeBunker
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A bit more information: I haven't fully decided what I'll do for the ceiling, but it'll probably be a drop something. I might end up making my own tiles, who knows. I'm not sure I can accept not being able to access my utilities - I change/add wiring way too often ;)

I hope to have most sound issues snubbed by my drywall + gg + insulation against the subfloor, and boxing in of ducting. Whatever ceiling I add beyond that hopefully won't need to have superior soundproofing qualities.
Make sure you have combustion air for your furnace now that you've sealed up the room.

Nothing prohibiting you form moving the return.. They usually put them central to the house so it draws air relatively uniform from the rooms.

As you noted, noise will be a concern.

Yes, as noted in the original post I'm already aware of the air supply implications.

I spent some time walking through the basement today, looking at where i would route various supply and return lines if I did or didn't move the trunks. Putting headroom aside for a moment, I'm thinking moving the truck line(s) would probably cause more sound problems than it would solve. Instead of having to box-in the trunk I'd end up with some very short ducts popping right off of the furnace and going directly into adjacent rooms. I'm thinking that furnace noise and noise shared between rooms will actually be worse this way. I'm starting to see the long trunks as an asset which I can use to obfuscate and diminish sound over a distance of varying duct size/type.

You may want to look through Geddes' book on the subject, starting at page 107, Duct Noise, free on his website:
Thanks for the link. I do already plan to use insulated flex duct on each leg. I've already done so on other parts of the house and the difference is remarkable. Even just stretching out a length and trying to talk through it with a friend gives you a good idea of what it does.

I don't think I need to go as far as building dedicated mufflers as suggested. In a way I feel that I would already have that since there would be no constant cross-sectional path from one room to another. Sound would first travel through a 6" round duct, then through a much larger trunk (3-6 times larger), then another 6" duct. In many cases you add a 3x14" rectangular duct into the line.

Anyways, the main question is whether I want to consider moving the trunks to save headroom and possibly improve soundproofing. As mentioned, I'm leaning toward keeping the runs as they are since I feel like shortening them would likely make the sound problems worse, and at best I'd only be getting back SOME of my ceiling, not all.

One compromise I could consider is kicking the smaller 8x12" supply to be right next to the return, rather than having that big space between them.

Then, if I'm not moving them I need to box them in. The question then is what is the least-bulky build style. Do I need to worry about framing/drywall touching the ducting (squeaks?). Should I wrap the ducts in something first? How would I box in the tops of the trunks if they're installed against the joists?
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