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HVAC Return Duct from Garage ?

Nolan Kienitz

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To begin with I know the IRC does not allow taking return air from a 'garage':

M1602.2 Prohibited sources.

Outside or return air for a forced-air heating or cooling system shall not be taken from the following locations:

1. Closer than 10 feet (3048 mm) from an appliance vent outlet, a vent opening from a plumbing drainage system or the discharge outlet of an exhaust fan, unless the outlet is 3 feet (914 mm) above the outside air inlet.

2. Where there is the presence of flammable vapors; or where located less than 10 feet (3048 mm) above the surface of any abutting public way or driveway; or where located at grade level by a sidewalk, street, alley or driveway.

3. A room or space, the volume of which is less than 25 percent of the entire volume served by such system. Where connected by a permanent opening having an area sized in accordance with ACCA Manual D, adjoining rooms or spaces shall be considered as a single room or space for the purpose of determining the volume of such rooms or spaces.

Exception: The minimum volume requirement shall not apply where the amount of return air taken from a room or space is less than or equal to the amount of supply air delivered to such room or space.

4. A closet, bathroom, toilet room, kitchen, garage, mechanical room, furnace room or other dwelling unit.

5. A room or space containing a fuel-burning appliance where such room or space serves as the sole source of return air.

On a recent inspection (new home construction) a fellow inspector noted a return jumper from a garage to the main return on the HVAC system plenum. Not hard to make note of ...

However, the home has the spray foam (possibly Icenyne) throughout and he (and myself) are wondering if changing the building envelope with the foam insulation has also opened up some possibilities for changes in HVAC design/installation?

I've been doing searches, but can't come up with anything that gives me direct link. I'll be making some calls to some HVAC contacts I have to help learn more, but thought I'd toss this out for observation here.

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I'm not clear on this. Are yoy saying the air handler/furn is in the house and the garage has a return it? Or, are you saying the the HVAC unit is in the garage with a grill cut in the plenum, with another grill in the garage wall goin to the return system in the house?

If they can pull a car in that garage, start a lawn mower or any type of engine in the garage with a return grill or a fresh air duct in the same space, carbon monoxide poisoning would be a concern of mine.

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Here we go with codes again!

Common sense would dictate that wherever there is carbon monoxide present you would not want to route it into your living space.

I would mention it and write it up.

Last thing one needs is the homeowner doing a tune up on his pick up and finding no one waking up the next morning.

I,m sure no inpsectorwants to see that article in the paper on one of his past jobs.

Happy new year

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Here is a bit more clarification:

HVAC unit is installed in attic over living space of home. Nothing unusual here.

Garage attic space is sealed off from attic over living space of home. This is good.

Normal return air duct(s) in place throughout living space of home. This is good.

Normal supply duct(s) throughout living space of home. None routed to garage.

Return duct (jumper) is routed from garage ceiling to HVAC return plenum chamber on HVAC unit. It is fully connected with no opens or blocks/dampers. The 'weird' one under question.

No supply duct(s) routed to garage. This is good.

Garage walls finished, textured and painted. (Maybe future planning of different use?)

Bottom line, as I noted in original post: It is wrong, was written up as such.

Home is of recent construction ... completed within the past 4-6 months. Located "out in the county" and away from any municiple AHJ or County Seat AHJ. Home was started before the new TRCC rules of phase inspections for "all" construction in the State of Texas no matter the location.

Inspector friend of mine has been digging as well, but we can only surmise that the original builder or buyer of home being built (he dropped out of original contract) may have had other uses planned for the 'garage'.

We're figuring it is one of the "Billy-Bob" moments we all see too often.

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I understand. I was a bit confused because in the original post you were talking about "insulation?'' I picked up on the return in the garage.

A jumper duct or a transfer duct typically does not connect to anything. it is merely a duct with a gill on one end with a duct going to another room with a grill on that end. What you have is a return grill in the garage ceiling going directly to the return plenum.

It may have been installed to serve as a supply grill but was hooked up to the wrong side of the HVAC system.

All in all, if the room has a large enough door to drive a car into this space, I would send a certified letter to someone letting them know that a dangerous environment exists. You better c.y.a. it as best you can.

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Originally posted by energy star

... I would send a certified letter to someone letting them know that a dangerous environment exists. You better c.y.a. it as best you can.

None of that is necessary ... could be warranted but a bit extreme. The inspector I was helping advised client of the situation in the report. It was well-noted and documented.

He also talked with builder and builder was contacting HVAC company to correct.

As I started the thread ... it was noted the installation was wrong/incorrect and not acceptable to the accepted IRC version. The question was relating to possibility of changes that various trades are experiencing or even experimenting with when it comes to such items as the Icynene (aka: foam insulation) installations.

Sometimes I see trades doing 'way strange' things with new items.

It is always an adventure.

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Just a guess, but maybe the HVAC guy was planning to use air scavenged from the garage to replace air in the home with a timer. We have systems in garages here with an air intake duct on a damper and a timer. They're set up to periodically open up and allow fresh ourside air to flow into the home through the returns as a fan in the home kicks in. Maybe this was the HVAC guy's intent but he's got his head tucked up his bottom.



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