Smokey fire

[angrybird]

Living on top of a mountain we get more than our fair share of wind! Storm Henry is blowing a hoolie today!
The problem is the open fire in our first floor lounge! On a day like today I have the fire lit but have to have the velux window open because of the bellows of smoke coming into the room. I have looked at anti downdraught cowls but any ideas how I could fix it to my chimney pot (and do they work)?

 

[Zebra]

Hello Angrybird. Hopefully someone knowledgeable will be along in a minute. In the meantime, I can whitter on for a moment I suppose. That's a strange chimney pot you have there, tapered towards the top. Does it have a lip at the rim? Otherwise, it could be quite tricky I suppose, to fix an anti-downdraught cowl. I assume this is the sort of thing you're talking about: http://www.fluesystems.com/shop/Chimney_Cowls_Static_Anti_Downdraught.html
I have one of those, and yes it does appear to do the job, but my situation is rather different: sheltered by houses, in the temperate South East, with a woodburner not an open fire. And a chimney to which I can strap it securely without it flying off in the wind (it straps around the pot under the lip, thus is unable to fly away).
If there is no lip, perhaps you might need to remove the top pot, down to where it is joined to the lower pot, and fix one to which you can strap a cowl. If your pot does have a lip, then you should be fine to try one of those.

 

[angrybird]

Thanks for your reply Zebra! There is no lip on the cowl and yes its a very strange pot! I will have a look at the link you sent ,in the mean time I will carry on looking like an extra from the black and white minstrels :lol:

 

[88v8]

That's very annoying.

You already have an anti-downdraught pot, on a very tall stack. Someone before you has visited this problem.
My next step would be an H pot, like this
http://www.ebay.co.uk/itm/Old-Original-H-Chimney-Pot-Reclaimed-/222005865940?hash=item33b094add4:g:SBQAAOSwX~dWpleU
That will stop downdraught, if that is the problem.

However....... what is the flue size? Looks like 9"?
And how big is the fire opening?

And how does air get into the room, is there a vent or are there for instance old windows with little gaps round them? When you open the Velux, does that just let the smoke out or does it stop smoking?

And is there another chimney in the house and does it also smoke? Or another fireplace that is open but not used?

Ivor

 

[angrybird]

Hi Ivor yes the pot is 9 inch and the fire is a typical tiled Victorian fireplace ...fire opening ...width 16" height 22" depth 12" (won't let me upload a photo!)
The fire only smokes on a windy day and its been very bad here for the last couple of days! I opened up the Velux to let the smoke out
I have 4 other open fires 2 working and 2 closed they are fine and never smoke
The "H" pot looks just the job as long as I can get one to fit my pot
Many thanks Jacqueline x

 

[Lewis Tiffany]

I wouldn't go for a normal rotary cowl it will pull too much air up if your in a exposed area .
Have a look at directional cowl's this will stop the down draft and reduce the wind noise across the chimney pot
It works like a weathervane and points the flue in the opposite direction of the prevailing wind .
Just make sure it well fitted .

 

[88v8]

Hi Ivor yes the pot is 9 inch and the fire is a typical tiled Victorian fireplace ...fire opening ...width 16" height 22" depth 12" (won't let me upload a photo!)
The fire only smokes on a windy day and its been very bad here for the last couple of days! I opened up the Velux to let the smoke out
I have 4 other open fires 2 working and 2 closed they are fine and never smoke
The "H" pot looks just the job as long as I can get one to fit my pot
Many thanks Jacqueline x

OK so 9 diameter = 63" area
16x22=352"
ratio 5.6. Shouldn't smoke.

Is there a door on the room? And doors on the rooms of the other fireplaces? Next time it starts smoking, shut all the doors. If that stops it, the problem is that air is being pulled downwards by the updraft on the other chimneys.

Does the offending room have an air inlet or old leaky windows?

That H pot I flagged up would replace your pot entirely. One can buy H inserts to sit on top of an existing pot, but probably not to fit yours, and in any case I think it would be unstable to fit a heavy ceramic insert on top of your already tall pot.

As Lewis observed, a directional cowl might help.
Here's one that looks rather like an angry bird
https://www.feature-fire.co.uk/product/aderyn-directional-cowl/
They do need maintaining however.

Ivor

 

[worms]

Could part of the problem be the tall, narrow, external chimney? Ours is a bit like that and in cold weather the cold outside air drops down the chimney and you can feel the down-draft into the room when you go to light the fire. Ours is a wood-burner rather than an open fire and we have learned to light an initial paper fire to warm the chimney air before adding too much smokey material. Get it wrong and the room is full of smoke! Does yours still smoke once the fire is up and running?

 

[Flyfisher]

Good question. In a previous house we had exactly that problem, especially when lighting the first fire of winter. The chimney contained a 'plug' of cold air that had to be expelled before lighting the open fire otherwise smoke would billow out into the room. Our solution was to light a large sheet of newspaper and hold it just below the flue of the fire. The resulting rush of heat would push out the cold air 'plug' and the fire could then be safely lit with no problems. If we had fires on consecutive days the residual heat in the chimney usually made the paper trick unnecessary.

I can also vouch for Ivor's H-pot suggestion. At the same previous house we were surrounded by tall trees, which would cause problems during windy weather with downdrafts. We fitted an H-pot insert to our bog-standard modern terracotta pot and it completely solved the problem. Unfortunately, I doubt an H-pot could be fitted to angrybird's rather striking pot so it would have to be a complete replacement. Also unfortunately, chimneys seem to have their own individual quirks so what works for one is not guaranteed to work for all of them.

 

[Lime]

Is there anything taller than the chimney nearby?
I've been down this route before and I found it was being cause by tall trees some distance from the house AND the shape of the leeward side of the house which, in the wind, caused a partial vacuum to be created on that side.
Air was sucked out of the house via leaky window and door frames.
Unfortunately an H-pot made no difference at all.
However perhaps your problem is not as bad because the smoke from my chimney was not a "puff" but more the total emptying of the chimney contents every large gust of wind.

 

[chuckey]

Some observations:- My BILs fire stopped drawing properly, turned out the horizontal part of his H chimney pot was blocked. Fires don't "smoke" because the hot gases rising from the actual fire are constricted just above the fire place. This causes a low pressure and room air is sucked up the flue at the top of of the opening and stops any smoke dangling about and ending up in the room. You have got a very thin stack, so the flue gases would be cooled on their way up it, so their velocity would be lower and hence the suction. Further restricting the flue gas speed would not be an advantage.
Frank

 

[a twig]

Hi Ivor yes the pot is 9 inch and the fire is a typical tiled Victorian fireplace ...fire opening ...width 16" height 22" depth 12" (won't let me upload a photo!)

OK so 9 diameter = 63" area
16x22=352"
ratio 5.6. Shouldn't smoke.

Coming from a world of dealing with nasty fumes in laboratories, the principle is the same, but the effects of getting it wrong are usually a bit more drastic and instant! I'm going to disagree with some other people here as well, so here goes!

Firstly, the fire seems quite tall and narrow, which isn't going to help things, the ideal height to width is 1:1 to 1:2, whereas yours is 1.4:1, so that will make things a little tricky.

The old rule of thumb used to be 1 inch of flue area for every 10 inches of fireplace area, so you're a fair way off that with your current 1 : 5.6
Also, the depth of the fireplace is only 12", so the aperture into the chimney is 12x22 = 192, which only gives a ratio of 3 at that point.

I would say that for this the fireplace, the flue is quite likely to large for the size of fireplace, which means your flue gas velocity will be too low, which will mean the smoke is cooling down too quickly before it gets high enough up the chimney, and thus on windy days when there is some air pressure resistance, the smoke comes back in. If you happen to have an anemometer lying around (small chance!) it would be interesting to know the face velocity at the fireplace on a still and on a windy say when the fire is lit.

The conical "reducer" on the top is clearly an attempt by someone previous to remedy this as its something I fit every day on extract stacks to increase exhaust velocity.

So, if it were me, two options:
1) a narrower liner and adaptor at the throat of the chimney
2) Larger fireplace frontal area, preferably with a better height width ratio

Neither will be cheap or simple, sorry!