Can anyone tell my if my furnace has a fresh air intake ?

I'm moved into my house a few months ago (Toronto, On, Canada) and noticed there are no pvc pipes on the outside of my house like all my neighbors do (for bringing in fresh air into the furnace).

On my furnace, I only see the venting pipe, which is shared with the hot water tank venting system.

My furnace is 25 years old and I was thinking of replacing it, but want to ensure I'm getting an accurate quote. enter image description here

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  • 2
    It has a fresh air intake, the real question is "where does the fresh air come from"? the basement?
    – Solar Mike
    Jan 2, 2023 at 22:07
  • So on the outside of my furnace room are 2 mesh vents. Does that mean it is only pulling air from the basement ?
    – Ronnie
    Jan 2, 2023 at 22:13
  • 1
    That is something you have to check and find out.
    – Solar Mike
    Jan 2, 2023 at 22:18
  • 1
    Age of the house might have something to do with it. If the house is older it might be leaky enough not to need special fresh air vents for the furnace.
    – crip659
    Jan 2, 2023 at 22:25

2 Answers 2


The PVC pipes for intake and exhaust are used with high-efficiency furnaces which extract so much heat that the exhaust glasses are cool enough to run through PVC. Those also draw combustion air from outside, to avoid having to use heated air from inside the house (drawing more cold air in to replace it).

Yours is not one of those. It does draw house air for combustion. That's how they all worked for a Very Long Time, so it isn't wrong, just not as efficient.


Your new furnace (replacing the current one in the picture) will very likely need a new combustion air intake (white PVC), independent from a fresh air intake.

Your current furnace has a knock out for combustion air intake using ducting from outside, but it is not used. That's probably fine, since it then draws in house air for combustion, through the grills of the furnace. Whether this is or was legal and safe depends on the quality of your building envelope, size of furnace room, presence and type of clothes dryer etc...

Combustion air intake is used for burning gas, and newer efficient models do not use your house air for that, but pull it in from the outside. This avoids unnecessary removal of indoor heated and moisturized air from being used as combustion air and then vented out.

Fresh air intake is used for maintaining indoor air quality. While the furnace fan is running it will mix fresh outside air into the heated stream. You very likely have that already, and it would show up somewhere in your return duct, usually close to the plenum near the furnace. It could be higher up out of site.

In older furnaces like yours it seconds as the combusion air intake, since the house air used up during combustion must be re-plenished or "made-up".

In your cold and dry winter climate it is beneficial to add a heat exchanger to the fresh air intake. Ask for a quote.

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