Cold air return

Did an inspection today on a single story home on a crawl.
The question is they are using the crawl space for the cold air return. There are no outside vents and no vapor barrier.

This is a first for me in 5 years. Is there an issue using the crawl.



2003 IRC M1602.1 Return Air. Return air shall be taken from inside the dwelling. Dilution of return air with outdoor air shall not be prohibited.

Are you sure about these words (in red)? That tells me it’s OK.



If this is a fueled furnace…Or is it a simple air handler for A/C only?

The return should not be in the same room as the furnace. The return/duct must be installed in a completely different room.

In a worse case scenario…If the furnace was to burn carbon monoxide, these deadly gases would get sucked right into the return and sent directly into the living area.

The return must be installed so it’s taking it’s air from anywhere other than the same room as the furnace.

FYI. There shouldn’t be any romex type wiring in the crawlspace. All wiring methods used in the crawl need to be plenum rated, such as MC cable or conduit. Doorbell, computer, phone and thermostat wire, also need to be plenum rated.

Jeffrey…what that says is that it is OK to introduce a small amount (typically 10%-15%) of fresh, outdoor air into the return air system. This is sometimes called ‘make-up’ air. The 1st sentence of the IRC caption is very clear…“Return air shall be taken from inside the dwelling” and leaves little room for interpretation.

A little added information. The furnace is not in the crawl space. It’s in the utility room and the return air is drawn fron the bottom. also there are no outside vents in the crawl so it is not getting outside air.


Very easy to get around that nonsense. Return air is not allowed to be taken from a non-conditioned space. Just as well take the return from the attic???

Ahhh…why didn’t you just say so to begin with ??? :mrgreen: :mrgreen: :mrgreen:


(Thanks for the clarification)