Hi all I have just restored two fireplaces in my 17th century thatched cottage back to as they were. However the down stairs fire smokes back into the room when the fire dies down , I have removed the modern ish 200mm chimney pot now it does not smoke so I am now debating on a 350 or 400mm pot as the flue is about 420x420mm or to build a dovecote with bricks . Obviously my concern is sparks .
- Thread starter bigduke
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88v8
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Hello and welcome.
The usual cause of smoking is a mismatch between the fire opening and the minimum flue diameter. If the ratio is worse than 8:1 it is likely to smoke.
I guess your fire opening is rather large, so by removing the 8" pot you have improved the ratio. It is odd however that the smoking is when the fire is dying down, commonly they smoke when first lit, while the flue is cold.
If the house is listed then the CO will have input, although within reason they will probably leave you to decide provided the solution is not unsuitable having regard to local architectural norms.
We have two woodburners in our thatched. One sees advice not to put a rain cap on the flues because of spark deflection, daft advice in a country where it rains.
How high does your chimney terminate above the ridge? You can of course easily add a couple of feet with a suitable pot, this with its top louvres would eliminate downdraft and add 4ft, but may look 'wrong'.
http://www.ebay.co.uk/itm/Chimney-Pots-4ft-/191789114847?hash=item2ca785a5df:g:xC0AAOSwqrtWojkc
Ivor
The usual cause of smoking is a mismatch between the fire opening and the minimum flue diameter. If the ratio is worse than 8:1 it is likely to smoke.
I guess your fire opening is rather large, so by removing the 8" pot you have improved the ratio. It is odd however that the smoking is when the fire is dying down, commonly they smoke when first lit, while the flue is cold.
If the house is listed then the CO will have input, although within reason they will probably leave you to decide provided the solution is not unsuitable having regard to local architectural norms.
We have two woodburners in our thatched. One sees advice not to put a rain cap on the flues because of spark deflection, daft advice in a country where it rains.
How high does your chimney terminate above the ridge? You can of course easily add a couple of feet with a suitable pot, this with its top louvres would eliminate downdraft and add 4ft, but may look 'wrong'.
http://www.ebay.co.uk/itm/Chimney-Pots-4ft-/191789114847?hash=item2ca785a5df:g:xC0AAOSwqrtWojkc
Ivor
Hi thanks for the reply the fire is used as an open fire and it is very similar to a rumford design,yes the main time it smokes is on start up with a cold flue, the smoke has to rise and then divert to the left through the throat and into smoke chamber.With the pot removed and the mortar remove when the fire gets going I am very happy with it,I will load some photos if someone could explain the procedure.I think a pot with internal dia of 350/400mm will be the answer if I can find one and this should give 1/7 ratio , I have found a new 350 mm pot but I think 400mm would be better
88v8
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- Glorious Gloucs
Perhaps your insurer is different, ours is keen that we have 6ft from chimney top to ridge. If so, you could comfortably put a rain hat on there. At lower heights there is more risk of embers being deflected onto the roof.
You could also use an H pot, like this
http://www.ebay.co.uk/itm/Reclaimed-H-Chimney-Pot-/301848106036?hash=item46478c9434:g:kL0AAOSwnipWbv2y
a rare antique example at a very low price. This type of pot is good at preventing downdraught and will keep the rain out.
As to the smoking, another way to improve the ratio might be to fit a smoke hood or glass blower.
And, of course, for air to flow up the chimney it has to be able to flow into the room. Over-thorough 'draughtproofing' can sabotage an otherwise viable fireplace. As can extractor fans in kitchen or bathroom.
Another problem is that if you have more than one chimney, there is always one flue that has more pull then the others. If the doors are open between rooms, in some conditions one can find that air is being pulled down one of the weaker flues. This tendency is worsened if the house has been over-zealously sealed so that there is no natural air percolation around windows and doors. Purpose vents inserted in suspended floors may offer a solution.
Or simply shutting the internal doors whilst lighting the fire.
If you have smoking while the fire is dying down, this is surprising as the flue will be hot and there should still be a good draught. I would therefore suspect that you may indeed be experiencing downpull from another flue. Try shutting internal doors, if any.
We had this situation in our previous house, where the flue in the bathroom was 'top dog' and led to sooty smells in the sitting room on warm winter days, even when neither the sitting room nor bathroom fires were lit. Took me years to work that one out.
Ivor
You could also use an H pot, like this
http://www.ebay.co.uk/itm/Reclaimed-H-Chimney-Pot-/301848106036?hash=item46478c9434:g:kL0AAOSwnipWbv2y
a rare antique example at a very low price. This type of pot is good at preventing downdraught and will keep the rain out.
As to the smoking, another way to improve the ratio might be to fit a smoke hood or glass blower.
And, of course, for air to flow up the chimney it has to be able to flow into the room. Over-thorough 'draughtproofing' can sabotage an otherwise viable fireplace. As can extractor fans in kitchen or bathroom.
Another problem is that if you have more than one chimney, there is always one flue that has more pull then the others. If the doors are open between rooms, in some conditions one can find that air is being pulled down one of the weaker flues. This tendency is worsened if the house has been over-zealously sealed so that there is no natural air percolation around windows and doors. Purpose vents inserted in suspended floors may offer a solution.
Or simply shutting the internal doors whilst lighting the fire.
If you have smoking while the fire is dying down, this is surprising as the flue will be hot and there should still be a good draught. I would therefore suspect that you may indeed be experiencing downpull from another flue. Try shutting internal doors, if any.
We had this situation in our previous house, where the flue in the bathroom was 'top dog' and led to sooty smells in the sitting room on warm winter days, even when neither the sitting room nor bathroom fires were lit. Took me years to work that one out.
Ivor