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Question DetailsAsked on 11/17/2014

Does code allow a cold air return to draw from the garage? There is no associated incoming vent to the garage.

My house (in Ohio) was constructed in the 1980's and has a cold air return that draws air from the garage. There is no associated air flow incoming to the garage. The cold air return was hidden behind some 5/8" drywall separating the garage from the family room. The only reason I discovered it is because there were a couple large holes in the drywall that I wanted to repair. I'm a little concerned about vapors entering the ventilation system.

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2 Answers



Garage = cars = carbon monoxide = death

You could seal it off

but disconnection to HVAC unit is best

then seal HVAC against drawing air from attic

Want to guess why it was there, then abandoned but suspect to being well sealed?

Answered 4 years ago by tgivaughn


As other comment said, NO - it is not allowed by code to come from the garage, and you have cause to be concerned. I would park outside until it is fixed, or at a minimum open the garage door before starting the car,, back out immediately, and leave the door open for 30 seconds or so it let the fumes dissipate before closing the door.

However, if the return vent opening is hidden in the wall itself, not open to the garage, then technically it is not drawing from the garage as that garage-side drywall layer is the dividing line bedtween house and garage - assuming it is properly air sealed (which I would not assume). Not clear from your description if you mean the duct is open to the garage, or pulling air from within the wall.

Couple of other issues here - you say there is no other air flow incoming to the garage - not sure if you meant no warm air duct feeding to the garage, or no outside air vent. If the former and latter both, then this duct is likely acting as the combustion air source for the furnace - taboo, and could also be putting a negative pressure on the living spaces that promotes infiltration of outside air around windows and doors and from attic and so forth - very bad from an energy efficiency standpoint, and also bad for air quality as unfiltered air would be drawn into the house.

If you meant there is no outside air source to the garage (typically about an 8" round screened vent or short screened piece of duct), then your funace is out of code anyway in all probability, because unless there is a dedicated combustion air duct to the furnace, you would not have a legal fresh (outside) air source of combustion air for the furnace (and probably a hot water heater too, if not electric).

However, as for blocking it off - I would advise against that until an HVAC tech confirms that is not being used as the make-up (fresh blending air) source for the furnace. I will bet that is acting at least partly (along with air leaking around the garage rollup or tiltup door) as the "fresh air" intake for the furnace. Shutting that duct off, if such is the case, can cause backdrafting or flame rollout of gas appliances in some cases, and also results in the furnace only circulating "stale" air through the house, without fresh air blending. That decreases your air quality, and can also cause pressure imbalances and decreased furnace efficiency in the home due to the fact there will not be as much return/fresh air available to the blower as it needs. Could also result in the system shutting itself down for that reason, if a draft pressure sensor detects negative (lower than atmospheric) air pressure on the incoming side of the blower.

I would say you need an HVAC contractor who is qualified to do ductwork layout, not just a service technician.

Answered 4 years ago by LCD

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