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Old 02-25-2011, 01:01 PM   #1
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Drywall used as return air duct??


Is that common or allowed by code that drywall will be used as two sides of the return air duct? There is nothing covered. Please see the picture. This is picture right before they put drywall on.

Thanks for your suggestions.
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Old 02-25-2011, 01:37 PM   #2
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Drywall used as return air duct??


I can't speak to the code, but a similar setup was done in our home and passed inspection. I will say it wasn't a new build so inspector probably couldn't tell how it was done. We had furnace moved from 1st floor to 2nd and there was no "cosmetically appealing" way to get the return duct another 10' higher.

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Old 02-25-2011, 01:50 PM   #3
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Drywall used as return air duct??


Yes it is common. It is also good to see the seems all sealed on the duct work with the paint on sealer.
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Old 02-25-2011, 02:14 PM   #4
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Drywall used as return air duct??


Joed - thanks for the replying, it makes me feel better. I thought there is always a pipe even for the return duct.

Moneymgmt - this is our first new house, just donot understand why the builder does so. It is ok if that is common.
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Old 02-25-2011, 03:04 PM   #5
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Drywall used as return air duct??


i didnt know you could do this either.

I know if you're using joist bay for return, it needs to be lined with sheetmetal. I wonder why that's not the case with stud bay?
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Old 02-25-2011, 03:07 PM   #6
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Drywall used as return air duct??


Not sure of your question on code compliance, but I think there is another question. The wire/cable running through the space, is it plenum rated?
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Old 02-25-2011, 03:51 PM   #7
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Drywall used as return air duct??


Nothing wrong with doing this in single family residential construction. In this area, all homes are done in this manner.

As for the wire, it does not have to be plenum rated to cross the space. It cannot run lengthwise (vertically in this case) in a return without being plenum rated. (It looks as if the romex has been wrapped in foil heat tape, which is silly and unnecessary.)
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Old 02-26-2011, 08:26 AM   #8
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Drywall used as return air duct??


Sheet metal ducting within a stud spacing is allowed here, but not with the Romex--a local thing. Metallic/plastic conduit would be necessary for just this one stud space. Go figure.
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Old 02-26-2011, 12:34 PM   #9
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Drywall used as return air duct??


It is allowed but NOT recommended. ACCA manual J ( the industry standard to residential duct design) does not recommended this method either.

This is a "cheap" way to allow return air. The friction rate is very high and and any turns, bends, offsets equal very long equivalent lengths of duct work.

This is typical in new construction were price is the deciding factor on which HVAC contractor gets the job. It also shows the builder is telling the HVAC guy how much room he can have for duct without any knowledge of proper duct design, friction rates, static pressures etc...

A professional HVAC companies will not do this type of installation and advise the builder the correct way.

As well, utility penetrations through the panned off joists are very limited. Electrical is allowed but no furnace vents, plumbing drains or gas lines are allowed.

This design provides very poor performance and extremely susceptible to leakage if not sealed.
Looking at your pictures; consider the sq/in between the bays and the sq/in cut in the base plate. I see a big difference.
Also the ratio (depth/width) in the bays are much higher than recommended by Manual J.

You will (no question) have very poor performance and high utility bills.

Get it fixed before they are finished. Hire a professional HVAC company to review it and provide you with documentation. Look for a company in your area that is trained and certified by National Comfort Institute.

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