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Furnace (gas)


Our furnace, which has a digital thermostat, will often not kick in on cold mornings. I've found that the exhaust pipe on the side of the exterior wall of the house often has a buildup os snow and ice. Once this is removed the furnace kicks back on. Why does this effect happen? How can I avoid it?


Dear Len:

To help you, I'll need to ask a couple of questions first:

1) Just so I'm sure, it's the "exhaust" pipe of your furnace that has the snow and ice built-up on it, it's not the "intake" pipe, right?

2) When you say that "the exhaust pipe on the side of the exterior wall of the house has a buildup of snow and ice", is the end of the exhaust pipe (which usually has a cap and screen) what is getting obstructed by the snow and ice?

If it is your exhaust pipe, and it is the cap and screen that is being blocked by the build up of snow and ice, then YES, this is likely why your furnace will not kick on until the blockage is cleared. When your furnace exhaust vent is blocked, not only can exhaust not get out, but air to your furnace's burner cannot get in. And without oxygen getting in, your burner cannot light.

So you need to be sure that the exhaust vent for your furnace does not get blocked with ice and snow. And to keep it clear, you should have a qualified service person configure your exhaust vent so the ice and snow does not block its flow.

In addition to preventing your furnace from starting, even partially blocking your furnace's exhaust vent can potentially be very dangerous for creating conditions where you can have carbon monoxide ("CO") building up in your house, as a result of incomplete combustion in your burner, or from the backing up or leaking of exhaust gases into your house.

I suggest that you make sure that your CO detectors are working properly, and that your furnace area is well ventilated until you can get a service person to inspect and better configure your exhaust vent, which I would suggest that you do as soon as possible.

Hope this is helpful.

Furnace (gas)