Smoke without a fire

December 7, 2006 6:18 PM

Why is there constantly smoke coming out of our chimney?

We live in an 80 year old brick house. The fireplace has been converted to gas by previous owners, although we've never used it or really even touched anything in it. The is a constant stream of smoke coming out of our chimney, although no fire is lit. It's about 10 degrees outside right now, although I think it has been doing this for a while at a range of temperatures. Why? Is it dangerous? What can we do to stop it? BTW, all the houses in our neighborhood are similar in design, and none of their chimneys are smoking.

posted by ubu to Home & Garden (18 answers total)

Best answer: Is your furnace on? Is it possible that the furnace also vents out the chimney?
posted by mr_roboto at 6:21 PM on December 7, 2006

When was the last time the chimney was cleaned? Is there the chance that soot inside it has been smouldering?
posted by malaprohibita at 6:28 PM on December 7, 2006

Best answer: There is no way it is smoke. It is likely condensation due to the heat escaping up the fireplace chimney and hitting the cold air. Like a jet trail. You are losing a lot of room heat through the chimney.
posted by JayRwv at 6:30 PM on December 7, 2006

Best answer: There should be a lever or control near your fireplace that allows you to close the damper. Sometimes it's up inside the chimney a little ways.

I agree with JayRwv: what you're seeing is almost certainly condensation, not smoke.
posted by Steven C. Den Beste at 6:35 PM on December 7, 2006

Best answer: I would go down into the basement (or wherever the furnace and water heater &c are), and check to see what is being vented. I wouldn't be surprised if it were something like the water heater venting into the flue.
posted by that girl at 6:37 PM on December 7, 2006

I second the furnace vent, and I'll add that your hot water heater probably also may vent there, as opposed to my mother-in-law who just vents to whomever will listen.
posted by Pollomacho at 6:37 PM on December 7, 2006 [1 favorite]

Response by poster: Thanks so much for the suggestions. My first reaction to seeing it was, "It can't possibly be smoke," but I will say that it is a steady, ceaseless stream that's been pouring out for weeks now, so it sure does seem like smoke at this point. Maybe this is a stupid question, but how do I determine whether the water heater and furnace are venting out of the chimney? It seems odd that ours would be the only house that these things vent out of, particularly since everyone has a pretty similar house around here.
posted by ubu at 6:49 PM on December 7, 2006

Response by poster: PS: JayRwv, I see what you're saying about the condensation. I misread you at first. That makes sense.
posted by ubu at 6:53 PM on December 7, 2006

If you really had a steady, ceaseless stream of smoke pouring out of your house for weeks on end you probably would have noticed that some part of it was on fire by now. My vote is for locating the vents and closing the damper.
posted by fshgrl at 6:56 PM on December 7, 2006 [1 favorite]

Any chance the gas burner in the fireplace has a pilot light that is burning? I think you better play detective and find out what is venting into the chimney. It should be easy if you check everything that produces heat and requires a vent.
posted by JayRwv at 6:58 PM on December 7, 2006

Sure it's your chimney and nobody else's?

Everywhere (UK and Ireland) I've ever lived, the flues from different fireplaces in adjacent houses often - but not always - join together on their way to the roof.

And, fireplace-heated homes usually have the hot water tank somewhere en route. Yours isn't heated by a fire now, but it might have been built that way. If your tank isn't properly insulated, you might be looking at condensation as hot water meets cold unused-chimney air.
posted by genghis at 7:01 PM on December 7, 2006

witches















Or perhaps your furnace or water heater vents into the chimney like in most homes. The latter is more likely but less fun.
posted by caddis at 7:33 PM on December 7, 2006

When it happens at my parent's house, it's because the (oil) furnace is running and it shares a chimney with the fireplace. It happens all year (well, you don't see "smoke" but a heat-rippled plume in the summer) b/c their furnace also supplies hot water for the house.

When it happens at my house, it's because my furnace is running - mine doesn't use a pilot and the hot water heater is electric (and I don't have a fireplace -- yeah, that's a bummer.)

I've never seen it happen just from indoor air leaking out through an open flue -- around here it gets pretty dry inside and out in the winter -- but that doesn't mean it isn't possible.

But definitely look into the possibility of witches - you can't be too safe.
posted by Opposite George at 10:20 PM on December 7, 2006

er, parents'
posted by Opposite George at 10:20 PM on December 7, 2006

The venting should be pretty obvious. There should be some metal pipe-type object (wide diameter) that goes from the top of the appliance to the approximate location of your chimney.
posted by that girl at 5:40 AM on December 8, 2006

I agree with most everyone. Your furnace and water heater which are most likely both gas, vent out to your chimney. the byproduct of gas burning is water which condenses into steam when it meets cold air. Steam does not equal smoke. Even your fireplace would not produce smoke if it was converted to gas.
posted by JJ86 at 6:30 AM on December 8, 2006

Response by poster: Thanks all. They do vent out the chimney. Still not sure why ours is the only chimney smoking, er, sorry, "condensing".
posted by ubu at 6:48 AM on December 8, 2006

Best answer: I'm no expert, but if the steam is constant, then I'd be suspicious. Your furnace and water heater don't run constantly (or they shouldn't, anyway). Maybe, like JayRwv said, you're venting the room's air up an open-flued fireplace?
posted by booth at 8:46 AM on December 8, 2006