Smoking log burner - Solved!

[Another Dave]

For years, seemingly at random, my log stove has smoked when being lit. I can tell it's going to happen because I can feel, by putting my hand in the stove, a draught coming down the chimney. We've just re-decorated the room with the stove after three years since the last time because it was filthy with smoke.

We vowed that if I felt the draught we wouldn't have a fire. Last night it happened and I went into the kitchen to tell my wife the bad news. She was cooking dinner and the extractor fan was going...

Switched it off - no draught, no smoke. The house must be so well sealed the extractor was sucking air down the chimney at the other end of the house. And yes, the room ventilator was open - it was sucking air through that as well.

Another Dave

[Martin Bonner]

Eeek! You may notice some improvement in your long-term health if you stop being intermittently exposed to carbon monoxide.

[Tim Watts]

Well done...

Given what you have discovered, you probably should install a 2nd vent in the room asap - or at least remove the fuse from the kitchen extractor. Or not use the fire for now.

Silly question - your current vent isn't blocked or fouled up with fluff is it?

You are now aware that the extractor can defeat the draw on the chimney under certain conditions...

If it were me, after installing a 2nd vent, I would test the fire cold with smoke matches with and without the fan.

And you do have a CO alarm don't you?

[Another Dave]

Eek indeed.

However, as I made clear, this only happens whilst the fire is being lit

- i.e. the fire is not drawing at all and the door is open. After less than a minute the fire was easily capable of overcoming the fan.

The smoke emitted during the lighting phase is the problem, there's no smoke at any other time.

And yes there's a CO alarm which doesn't go off and two smoke alarms which sometimes do (not surprisingly).

Another Dave

[Another John]

Well done :) I was going to suggest lighting a scrumpled up sheet of newspaper and burning that on top of your laid fire, in order to give it a "re-heat"[1] type start.

J. [1] Not a good metaphor I know.

[Another Dave]

That's exactly what I was doing! However it still created some smoke and the decorations were ruined before I discovered your method.

All's well now.

Another Dave

[Tim+]

Hmm, I'm more inclined to believe the OPs observations than an armchair expert.

Tim

[Tim+]

Are you presently in the OPs house? No. I agree that many chimneys need "warming" to encourage convection but you don't know how well sealed the OPs house is.

Tim

[Brian Gaff]

Now I'd have thought it was cold air falling due to the cold chimney outside the house, so you live and learn. Brian

[Dave Liquorice]

Ours isn't with exception of very still (ie smoke rises straight up) and cold (close to or below 0 C). Any other conditions and there is a draw.

[cl]

Both are right in a sense I think.

We have a wood burner which draws pretty well in most situations but as suggested you do always need to get a bit of initial heat (with paper or whatever) to get a draught up the chimney. However with some very specific wind directions the chimney isn't quite high enough to avoid eddies around the house creating a significant down-draught. When this happens we have to open the front door (right at the other end of the house) until the fire is really quite hot and then there is enough up-draught to overcome the wind.

I guess the kitchen extractor may well be a similar effect to our particular wind direction, it just means that the log fire has to create a bit more up-draught than normal.

[Martin Brown]

They shouldn't ever leak smoke into the living room though.

And any smoke during lighting usually indicates that the kindling was damp. On really cold days I have seen condensate form on the front window when lighting the fire but I have never seen smoke fail to leave the combustion chamber unless something was wrong.

I'm slightly puzzled too since the fire should catch pretty quickly and the hot air in the stove from the initial paper fire should pull any smoke back up the chimney in under a minute. If it doesn't then it tends to suggest something is wrong with the flue or backplate - build up of ash or soot fall or something else blocking the exhaust path.

Had that happen to me once. When was the chimney last swept?

[JimK]

?? ever?? nah

not uncommon IME if climatic &/or geographic factors arent optimal...

Jim K

[Martin Brown]

With an open fire I'd agree it was always a problem when a strong gusty wind was in the right direction to cause blowback of smoke and/or pull air out through another unused fireplace but since putting the wood burner in it has performed admirably even in gale force conditions.

Obviously YMMV

[Mike Barnes]

Ours does, especially if the chimney is really cold. I always start by burning a couple of sheets of newspaper to get the air moving upwards.

[JimK]

/Obviously YMMV /q

Persackerly.

your rose-tinted experiences do not the truth maketh....ever:-)

Jim K

[Dave Liquorice]

If ours has the initial bit of smoke from the very first bit of paper lit make its half hearted attempt to come into the room within seconds of the paper really burning it gets drawn back in and up the chimeny.