Thread: Return Air

Hello All,

I am looking for your thoughts and opinions on stud space being used for return air (and the related pan deck) specifically as it applies to 2006 IRC M1601.1.1 #5 and #7.

Pro's and con's. Problems you have seen in the field. Do you like these systems? Don't like them? Inspection considerations during and after construction inspections.

This is unrealted to H.I. work.

Thanks,

Corey

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The only Pro is that it saves the contractor money.
The Cons:
- essentially, dirty unverifiable return cavity, read normal construction dust and debris that gets into cavities during construction that no one cleans out
- mold issues once the drywall gets hit with any water
- during construction inspections its common to find damaged/gone top plates and hacked framing at the ceiling level from a wild HVAC guy
- OR the HVAC guy just drilled a bunch of holes into the top plate for air passage; no of course air flow is severely restricted, so much for good return air
- chopped up floor joists also aren't uncommon
From my experience most Muni inspectors, both City and burbs have moved away from signing off on any return chases without a pan liner. Over the last few years I've also seen more contractors moving away from using cavities for return because of the cost indifference. Once you factor in pan liner cost and labor to deal with that and potential Muni inspector issues; often times it seems easier just to re-route and run a dedicated duct.
The main problem comes down to air quality. Whatever is in the return air stream can get pulled into the furnace and distributed throughout the home instead of just being isolated in one area. Sure the ducts can get dirty. However, the ducts aren't susceptible to the same level of organic growth and potential hazard; unlike drywall and wood.

Originally Posted by Corey Friedman

Hello All,

I am looking for your thoughts and opinions on stud space being used for return air (and the related pan deck) specifically as it applies to 2006 IRC M1601.1.1 #5 and #7.

Pro's and con's. Problems you have seen in the field. Do you like these systems? Don't like them? Inspection considerations during and after construction inspections.

This is unrealted to H.I. work.

Thanks,

Corey

Radon. Structure always communicates with earth. Infiltration, condensation, drag, MC variations in floor or wall system, rodent and insect pathways and nesting areas, FB, cosmetic issues -finishiing on the exposed wall surfaces, fire resistance, noise, etc. One tear, scratch to the gyp paper, DIY or "professional" duct cleaning service destroys integrity regards fire resistance properties of the the gyp board panel, now exposed gyp becomes particulate matter source erroded by air stream, even low wc.

Nope.
Yep.

M1602.2.

More than one story, one family, NG.

Don't think it will fly or work well in new const. in Cook Co. or NE Illinois 'cept maybe for heat only hydronic coil; naw, still nope, climate too extreme, and Radon - your clay & water table issues, what's not there today WILL be there tomorrow.

- 5. Use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125°F (52°C) and exposed surfaces are not subject to condensation.
- 7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- - 7.1. These cavities or spaces shall not be used as a plenum for supply air.
- - 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- - 7.3. Stud wall cavities shall not convey air from more than one floor level.
- - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

The joist space turns and goes up at the end into the stud space and the required fireblocking of that stud cavity has now been removed - not allowed per R602.8.

The air handler is on the first floor and the stud cavity conveys the air from the second floor through that stud cavity - not allowed per 7.3.

Plus everything Markus and Watson brought up, including this from Marcus: "The only Pro is that it saves the contractor money."

I don't have a problem with it. The entire house is a return plenum as it is.

Maybe in areas of higher humidity it is a bigger concern.