Thread: HVAC Return Jumper Duct from Garage ?

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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The exceptions aren't dependant on the type of insulation in or around the room in question, so I would say a "garage is still a garage", Icynene or not.

As foam insulation typically "tightens up" a structure, absent some sort of mechanical ventilation introducing exterior air would not such a structure retain carbon monoxide from vehicle exhaust longer than a conventionally insulated structure? If that's the case the tighter insulation would if anything make the problem worse...

No exceptions, Nolan. Dom has it right, a garage is a garage.

The thermal barrier for energy has nothing to do with the required separation between the house and garage.

I can't imagine any reason to put in a return air duct to the garage if there is no supply to that "room" anyway.

I suspect maybe that would be a fresh air intake that was supposed to go to the outside or a return duct for a master bedroom, etc. In any event it is wrong, wrong, wrong.

Just curious, did they have the foam on the roof deck and the attic floor over the garage or some other arrangement?

The reason for no return air from the garage is so as to not draw noxious and unwanted fumes from the garage into the living space.

Types of noxious and unwanted fumes stored in a garage are: gasoline (stored in storage tanks such as vehicle gas tanks, lawn mower gas tanks, spar gas cans, etc.); lawn fertilizers and pesticides; solvents and other cleaners; oil; etc.

Thus, as Dom said, it does not matter what type of insulation is installed, you want to keep the garage and its air separate from the living space and its air.

Are you (is he) sure that it went from the garage to the house duct work?

Nolan, you have the right info to confirm the prohibition, but I too would like to know "what were they thinking?"
If you find out, please let us know.

I think I know what Nolan is describing, but then I might not. Lets see if this is what he is talking about.

The HVAC unit (furnace, blower and A-coils) are in the garage. The return air is being drawn from inside of the home but the return duct is entering the garage and back to the unit. No return air is being drawn from the garage, I think.

Originally Posted by Scott Patterson

I think I know what Nolan is describing, but then I might not. Lets see if this is what he is talking about.

The HVAC unit (furnace, blower and A-coils) are in the garage. The return air is being drawn from inside of the home but the return duct is entering the garage and back to the unit. No return air is being drawn from the garage, I think.

I'm going with another thought of what Nolan is describing: There is a return jumper cut into the garage which then connects back into the main return duct, with that return jumper being open to the garage.

That's how I read the post as well...

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

As noted in bottom bullet there could have been some future planning in mind, but there were no supply ducts routed to the garage. BUT ... future planning would have to include making the 'garage' not usable as a 'garage' to make the installed return acceptable.

Just talked with an HVAC contractor and he agreed (as I knew he would) and also was not aware of any exotic HVAC systems and/or 'out of the box' changes with respect to the foam insulation and changes in the home's envelope.

This is a new home construction "out in the county" and well away from any city/county seat code official inspection. Home was started before the required TRCC phase inspection plan was kicked into gear last September.

Likely is one of the oft-referred to "Bubba Moments".

Saw a similiar situation a few years ago. Furnace was in the garage (for some reason) and a return vent was cut into the return air pleunm. I wrote it up as being improper.