Soot Stains Near Heat Vent: Possible Causes

LESLIE: Dan in California, you’ve got The Money Pit. What can we do for you?

DAN: I have black soot coming out of my heater through the vent, through the wall. It’s a wall mount heater. And it’s all over the outside of my building.

TOM: Huh. That’s not good. So, this is coming – you say, it’s – is it coming out of the vent for the – through the wall heater?

DAN: It’s coming out of the vent. I pulled the cover off where the burner is.

TOM: Mm-hmm.

DAN: Down at the bottom.

TOM: Right.

DAN: And there’s black soot all over the – I guess you call it a heat exchanger.

TOM: Dan, you’re talking about this soot being on the outside of the building, correct?

DAN: Outside of the building and on the – all over the inside of the combustion chamber of the heater.

TOM: OK, but it’s on the combustion side. It’s not on the house air side, correct?

DAN: Well, there’s a little bit of black soot even coming into the house.

TOM: Alright, this isn’t right. It sounds to me like the cause of this problem is an improperly adjusted gas flame; which is why you’re getting so much carbon. But the fact that you’re getting this inside could mean that you have a cracked heat exchanger and that can be very dangerous. So you need to have this system inspected by an experienced person; maybe a person – someone working for the gas company or an HVAC contractor to look at the heat exchanger. Because the life of the furnace is really determined by the life of the heat exchanger.

And for those that are not familiar with what a heat exchanger is, it basically is what keeps the combustion gas separate from the house air. Imagine a hot water radiator where water circulates inside and air blows over the outside. That’s kind of what happens inside of a gas furnace. But what’s circulating inside of the heat exchanger is combustion gas. That could be …

LESLIE: So we need to be concerned about carbon monoxide in the house.

TOM: Correct. Could have carbon monoxide. If the heat exchanger is cracked [or voided] (ph) or rusted out then that could be leaking out and getting into the house air side.

LESLIE: Do you have a CO detector, Dan?

TOM: Well, it’s always a good idea to have a CO detector but sometimes CO detectors – you know, it takes an awful lot of gas to make them go off. I would say that you definitely need to get this inspected right away.

How old is the furnace, Dan?

DAN: Oh, I’d say four or five years old.

TOM: It’s not that old. So you probably may just need to be able to get it cleaned. But you’re not going to know until you get all that soot off there and try to figure out what’s going on. It’s definitely not set up right. Dan, get to that right away because it could be dangerous.

Thanks so much for calling us at 888-MONEY-PIT.