Strange smoking fire problem – what are your thoughts?

[Manny]

Our house is on four levels including a cellar. The chimney extends from the cellar to the roof. At some point there may have been fireplaces in the bedrooms at first and second floor levels but they are no more having been bricked up.

The fireplace in the cellar remains and we have just recently had a lovely old work of art installed in the living room on the ground floor. Last night was the first proper trial of it. I lit a decent fire in there and all was well for about fifteen minutes until I noticed that the room was becoming increasingly smoky.

I stepped into the hall to open the front door and noticed smoke was emanating from the cellar doorway too and the hall was filling with smoke. On further inspection, the cellar ceiling was covered in a thick layer of smoke.

The heating the cellar is temperamental at best and the radiator has just decided to stop working yet again. It’s pretty cold down there and we leave the door open to get a nice draft through it, as there’s a well ventilated window light in there.

So the question is, what’s going on? The fire itself draws very well, flames lick the back of the fire and are drawn up the chimney. Could it be that a little smoke isn’t being drawn up and is seeping into the living room and through the floor to the cold cellar?

I shone a very powerful torch up the cellar chimney and looked up the living room chimney but there was no sign of light at all. Could it be that the flues are connected further up and smoke is being drawn up one and down the other?

Has anyone experienced anything like this? I’m not sure I really understand why smoke would migrate from a warm room to somewhere cold. Is there too much of a draw from the cold cellar because of the draft? Would it help to light both fires at once... is that what you're supposed to do?

Many thanks!

 

[Lime]

I suspect that this is a common problem of years ago.
The smoke from one chimney is sucked down another.
It happens when the draught of the lighted fire is not matched by outside air coming into the house.
As a result air is either drawn down other open fireplaces or the fire smokes or both.
Weather conditions can make it worse too.
The way most people used to get over the problem was to fit a taller pot on the chimney.
(or open a window in the lighted fire's room)

 

[Mark]

have you been up on the roof and had a look at the chimneys? what are the pots like - any cowls or similar?

When was the chimney cleaned last ? Check to see if the brushes come out of th same pot from the cellar and the main room. Also a suitable weight on a rope lowered down - see where it comes out.

 

[worms]

Maybe I have misunderstood the problem here, but it would seem to me that the most likely cause is that the chimney is cold and until it heats up it will be trying to suck air down. If the two fires join further up, all the smoke from the living room fire and its now warming flue will be sucked back down the cellar flue until such time as the combined flue warms sufficiently to draw.

Could you light a non-smokey fire (newspaper etc) in the cellar fireplace to warm that air flow at the same time as you light the living room fire? An alternative might be to put an electric fan heater in front of the cellar fire so that you have a warm airflow directed up the chimney until it all warms up.

Was it a particularly cold evening when you tried to light the fire? My chimney sucks on odd occasions, and is related to the warmth of the house and the outside temperature. I now tend to put my hand in front of the fire to see which way the air movement is, prior to lighting - verified by watching the flame on the match. If it is sucking, a few nightlights left in the bed of the fire for 10 minutes before lighting with newspaper seems to be enough to prevent a room full of smoke.

 

[Manny]

Thanks a lot for the replies, appreciated as always. I've done a fair bit of research this morning and now I have a much better understanding of the hugely complex nature of the potential problems.

From what I've been able to ascertain the two flues must combine towards the top of the chimney. As the cellar was very cold yesterday because of the malfunctioning radiator my guess is that the cellar was at a lower pressure than the warmer air rising up from the fire. The cold cellar flue has indeed sucked all the smokey air down that's been trying to escape out of the chimney.

What I think I need to do is seal off the ventilation in the cellar to some degree and make sure it's nice and warm to create a higher pressure so that the chimney sucks air out instead of in.

There are other complications as well, such as the amount of air entering the house at higher levels (the loft hatch was off last night on the second floor). It's a juggling act to balance the air flow but with some experimenting I'm confident I can solve the problem.

Thanks!

 

[MdB]

As the cellar was very cold yesterday because of the malfunctioning radiator my guess is that the cellar was at a lower pressure than the warmer air rising up from the fire. The cold cellar flue has indeed sucked all the smokey air down that's been trying to escape out of the chimney.

What I think I need to do is seal off the ventilation in the cellar to some degree and make sure it's nice and warm to create a higher pressure so that the chimney sucks air out instead of in.

Be careful about your thermodynamics here. The cold air in your cellar will not produce a lower pressure. Heating it up will not produce a higher pressure. This would only happen if you made your cellar completely air tight.

There may well be a lower pressure in your cellar but this is probably due to the outside wind blowing around your house in such a way that it produces a lower pressure at the ventilation point in your cellar than at the top of your chimney stack. This lower pressure is then sucking the air down the chimney. (Of course there is no such thing as suck but I will leave that to another arguement)

 

[Penners]

Be careful about your thermodynamics here.

Don't you start, MdB! We're having quite enough trouble with NT on another thread!

 

[worms]

I don't think we need to get into any complex thermodynamics and pressures in different parts of the building. Air in a cold chimney will surely tend to fall. Until the chimney warms and overcomes the tendency for the air to drop down the chimney, the smoke will come down rather than go up. If you are warming one chimney and it joins another cold one, then the smoke will want to go up one and down the other until such time as the combined flue warms sufficiently, which it probably will do if you persevere with the fire - unfortunately this may not be before the cellar fills with smoke!

Why not humour me and try the electric fan heater in front of the cellar fire (pointing into the chimney) to see if you can warm the combined flue?

 

[Nemesis]

Our house has two flues (combined are not usual apart from in very old houses...) together, when it's cold the smoke goes out of the pot and is drawn down into the bedroom which is cold.

A pre-warmed flu does indeed help a fire draw.

 

[Manny]

Thanks again for the info. I did try again on Friday and this time I made sure that the cellar was heated (fixed the radiator... again!) and reduced some of the air flow coming in through a broken roof light in the cellar.

I built a fire in the living room and a smaller one with some kindling in the cellar. Then lit the cellar fire to get the flue nice and warm before I lit the fire in the living room. It drew pretty well.

Only problem was... the living room started to fill with smoke because the smoke was going up the cellar chimney and down the living room chimney... ARGH!

So in desperation I lit the living room fire. Yep, you guessed it, the fire in the cellar stopped drawing and the cellar filled with smoke. So I put both fires out and called it a day.

I'll certainly have a go at using an electric heater to get the flue warmed before I start next time. I'll let you know what happens.

 

[Manny]

Right, update on this saga. I've tried many experiments to get this working. I've opened and shut just about every door and window in the house in every possible combination, shut the loft hatches, etc, etc.

Tried to reduce the draw of the basement fire by blocking up the flue as best I can (with wedging a nice big plank against the opening and blocking up the gaps with dust sheets) - didn't work, somehow smoke still filtered through albeit at a reduced rate, and I thought I'd done a reasonable job too!

Worms - I had a 2kW fan heater aimed up the flue for 30 minutes before lighting the living room fire. All was well for about 10 minutes then the smoke started pouring out of the basement fireplace. I kept the heater there, it helped but the basement was still smoky and from time to time the living room fireplace would blow back smoke into the room.

So, my only option now is to get someone to take a proper look. I suspect that there's some damage/breach of the flue(s) somewhere up there.

 

[Lime]

This seems a strange fault.
Initially your description could have been several things but your detailed description of your attempts to stop the fumes convinces me that something is not right with the chimney.
One of the details you haven't mentioned is whether or not you are getting smoke coming out of the chimney pot.
I have seen chimney pots so blocked with soot that the smoke shoots out of them as if they were straws.
Have you had the chimney swept?

 

[worms]

Good point, Lime! I hope we have not missed the obvious here!

If the chimney is clear and nothing else seems to work, would a fan assisted flue be an option? Never known anyone with this but its been mentioned on here in the past.

 

[Manny]

I did have the living room flue swept, but I wasn't present at the time so I can only assume he did a propper job. As the basement stairs aren't the most stable creation the old guy refused to sweep the cellar chimney!

It's difficult to see the pots unless I stand at the very bottom of the street, so I haven't checked what's actually happening to the smoke. As both fires draw well when lit, together with the fact that the smoke can get into either flue from either fire, I had assumed that they converged somewhere near the top and used the same pot. Perhaps it's worth having the cellar flue swept before I go down the expensive survey route.

 

[Lime]

Good point, Lime! I hope we have not missed the obvious here!

If the chimney is clear and nothing else seems to work, would a fan assisted flue be an option? Never known anyone with this but its been mentioned on here in the past.

In the past when sweeps were commonplace it was not unusual for some not to be able to reach up 4 storeys, the usual need being for just 2 floors, so long flues often didn't get completely swept. If this is the case then the upper portion of the chimney may be nearly blocked. The better sweeps used to be proud of the fact that their brush was showing out of the pot and invited the householder to witness it.
Also the chimney sweep rods/poles were much more rigid than some made now and couldn't negotiate difficult or awkward flues and it was not totally unknown for the brush to come unscrewed up the flue often with some rods attached too! I remember seeing a sweep on a roof attempting to push/knock down the "lost" brush in the chimney he had been sweeping. Sometimes I suspect it was just left in the chimney.

As far as fan-assisted flues are concerned I have found them to be noisy and I'm not sure they would improve this problem unless there is a fan in each flue.

I did have the living room flue swept, but I wasn't present at the time so I can only assume he did a propper job. As the basement stairs aren't the most stable creation the old guy refused to sweep the cellar chimney!

It's difficult to see the pots unless I stand at the very bottom of the street, so I haven't checked what's actually happening to the smoke. As both fires draw well when lit, together with the fact that the smoke can get into either flue from either fire, I had assumed that they converged somewhere near the top and used the same pot. Perhaps it's worth having the cellar flue swept before I go down the expensive survey route.

Perhaps the flue hasn't been completely swept? It wouldn't surprise me.
Anyway sweeping the cellar chimney sounds a very good idea and I would have the livingroom one done again just to make sure (with a different sweep). Also make sure they go right up the chimney and out of the pot!

If the sweeping does not improve things I would light a fire alternatively in each grate and check the pots for smoke with binoculars.
At least you will have some confirmation or not of a conjoined flue or faulty chimney flues.