Down draft causing a smoking fireplace
The term 'Downdraft' is used very loosely and for most of the problems associated with smoke spillage.
In reality constant downdraft is very rare but for us the first indication would be a noticeable smell of acrid soot as soon as we walk into a room even when if fire has not been alight.
Our advice when experiencing downdraft problems ;
This is how we test for a downdraft...
Tools:
1. A light weight thin cotton sheet like a bed sheet large enough to cover the doors to the room.
2. Tape or drawing pins. I normally use Duct tape but make sure the tape being used does not damage any surfaces.
The fire must not be alight and you will need to choose a day with some wind.
The four examples below we have picked show the varying degrees of strength of intermittent downdraft and how we tackled them. Some of the causes of the downdraft we found were so unusual that they were impossible to predict beforehand. The secret is to be patient and persistent with the testing.
A customer in the Cotswolds had a metre square fireplace opening served by a flue that was too small. On the advice of the sweep he also had a spinning cowl fitted to try and increase the draw on the flue but this didn't work.
We completed tinfoil tests but even with the smallest opening smoke spillage kept occurring. After resorting to a sheet test on the lounge door we quickly found that air was being drawn out of the room and hallway by a low pressure area outside the front door. This could not easily be stopped as the timber framed house was naturally draughty so windows were opened slightly on the windward side of the house and together with progressive draft exclusion to the front door and front windows the fire eventually began to work correctly .
A lounge fireplace in a dormer bungalow was being affected by the position of the house in relation to the prevailing winds. Here tests revealed that air was being drawn out of the front door letter box and trickle vents in the windows as the wind passed over the house creating a partial vacuum.
Two vents were added to the lounge on the windward side to give the fire more free air and balance the pressure differences air but intermittent downdraft problems still occurred when the wind speed increased. As the letter box, door and vents were always in use we turned to strengthening the draw on the fireplace by increasing the height of the chimney. This was tested by adding a metre length of single wall flue pipe secured to the pot and the difference in function was an instant improvement. The chimney was used and thoroughly tested in various weather conditions for several months before being rebuilt slightly higher than the test length, just for added peace of mind!
We had a case like this in Sussex where the fire did not respond that well even when the window was open. The air was been drawn out of the room and up into the stair well toward a Velux roof light which tended to be left open. The stairs and open Velux acted like a chimney and fought against the lounge fireplace but once the window vent was shut, and the chimney effect stopped, the fire worked well.
A long two storey listed 15th century timber framed farm house in the Vale of Evesham with a single storey brick built kitchen and Inglenook fireplace, built in the Victorian era on one end, is the setting. This kitchen was large enough to be used as a second lounge or snug so a canopy was introduced to the inglenook to reduce the air necessary to make it function correctly. The fireplace spilled smoke despite having ventilation and after testing for downdraft we discovered a large volume of air being drawn into the main house under the connecting doorway and around the frame. The kitchen, two lounges and dining room in the main house all had large fireplaces and big flues which were open and at least 9 metres tall. With no dedicated vents in each of the rooms the flues were tall enough and large enough to generate enough low pressure to pull air in from every available hole in the house including down the snug flue which was half the height and capacity.
Every part of the snug door including the key hole was sealed and the fire worked but although the cause was discovered the remedial work to introduce more air into the main house, so as not to totally isolate the snug, we understand is still ongoing!
Finally
Downdraft problems in public houses or hotels are invariably caused by the kitchen extraction system no matter how may rooms away it is situated and is usually only cured by adding a chimney extract fan to the top of the flue.
In reality constant downdraft is very rare but for us the first indication would be a noticeable smell of acrid soot as soon as we walk into a room even when if fire has not been alight.
Our advice when experiencing downdraft problems ;
- We like to be absolutely sure we are dealing with downdraft and if not then we run the 2 minute 'Draw Test' first and possibly the Tinfoil test as well afterwards
- We don't advise spend any money on cowls
- We always test to see where the problem stems from first
- It's best to test your theory to overcome the problem for a period of time
This is how we test for a downdraft...
Tools:
1. A light weight thin cotton sheet like a bed sheet large enough to cover the doors to the room.
2. Tape or drawing pins. I normally use Duct tape but make sure the tape being used does not damage any surfaces.
The fire must not be alight and you will need to choose a day with some wind.
- We normally isolate the fireplace from the rest of the house by closing all the doorways in the room preventing the influence of other parts of the building. We cover the faces of air vents within the room and in any adjoining rooms with newspaper or tissue, this enables us to check for inward air movement. If air is being extracted from the room the tissue will be pulled tight on to the vent face
- If there is more than one fireplace in the room then we sheet this too to establish whether this is the culprit robbing all of the available air or if it is also sacrificial to a stronger vacuum
- If there is more than one door to the room we usually test them individually keeping the others closed and draft excluded across the base with another sheet
- We open one door and cover the whole aperture loosely with the sheet leaving no gaps around the frame. We tape the sheet to the door frame or use drawing pins along the top edge, which are not visible, if we are testing for a few minutes. The sheet should respond instantly if air is being pulled out of the room with the speed and strength of the pull being an indication of the low pressure pulling air down the chimney
- We test each door in turn if there is more than one and try to establish which is mainly responsible for the issue
To do this we may have to continue testing other doorways in the house systematically following the strongest low pressure to its source before finding a reason for the problem. The movement of the sheet indicates the direction in which way to travel next. It is important not to underestimate two and three storey staircases as they can act like a chimney and draw air away from a flue system too - When the sheet is being pulled into an adjoining hallway or room it is always worth opening a window near to the fireplace to test the impact on the sheet. The window opening can be adjusted until the sheet hangs loose which will indicate the size of air vents needed to over come the low pressure.
- If we can easily find a reason for the constant or intermittent movement of air down the chimney then a cure can be established but if ideas have run out there are other things to consider such as; poor flue position in relation to the adjoining roof or neighbouring building, overall height of the flue or a courtyard or garden area acting as a low pressure zone pulling air out of the house
- All of these issues can be tested without resorting to guesswork but it is always worth remembering that there may be more than one factor causing the problem
The four examples below we have picked show the varying degrees of strength of intermittent downdraft and how we tackled them. Some of the causes of the downdraft we found were so unusual that they were impossible to predict beforehand. The secret is to be patient and persistent with the testing.
A customer in the Cotswolds had a metre square fireplace opening served by a flue that was too small. On the advice of the sweep he also had a spinning cowl fitted to try and increase the draw on the flue but this didn't work.
We completed tinfoil tests but even with the smallest opening smoke spillage kept occurring. After resorting to a sheet test on the lounge door we quickly found that air was being drawn out of the room and hallway by a low pressure area outside the front door. This could not easily be stopped as the timber framed house was naturally draughty so windows were opened slightly on the windward side of the house and together with progressive draft exclusion to the front door and front windows the fire eventually began to work correctly .
A lounge fireplace in a dormer bungalow was being affected by the position of the house in relation to the prevailing winds. Here tests revealed that air was being drawn out of the front door letter box and trickle vents in the windows as the wind passed over the house creating a partial vacuum.
Two vents were added to the lounge on the windward side to give the fire more free air and balance the pressure differences air but intermittent downdraft problems still occurred when the wind speed increased. As the letter box, door and vents were always in use we turned to strengthening the draw on the fireplace by increasing the height of the chimney. This was tested by adding a metre length of single wall flue pipe secured to the pot and the difference in function was an instant improvement. The chimney was used and thoroughly tested in various weather conditions for several months before being rebuilt slightly higher than the test length, just for added peace of mind!
We had a case like this in Sussex where the fire did not respond that well even when the window was open. The air was been drawn out of the room and up into the stair well toward a Velux roof light which tended to be left open. The stairs and open Velux acted like a chimney and fought against the lounge fireplace but once the window vent was shut, and the chimney effect stopped, the fire worked well.
A long two storey listed 15th century timber framed farm house in the Vale of Evesham with a single storey brick built kitchen and Inglenook fireplace, built in the Victorian era on one end, is the setting. This kitchen was large enough to be used as a second lounge or snug so a canopy was introduced to the inglenook to reduce the air necessary to make it function correctly. The fireplace spilled smoke despite having ventilation and after testing for downdraft we discovered a large volume of air being drawn into the main house under the connecting doorway and around the frame. The kitchen, two lounges and dining room in the main house all had large fireplaces and big flues which were open and at least 9 metres tall. With no dedicated vents in each of the rooms the flues were tall enough and large enough to generate enough low pressure to pull air in from every available hole in the house including down the snug flue which was half the height and capacity.
Every part of the snug door including the key hole was sealed and the fire worked but although the cause was discovered the remedial work to introduce more air into the main house, so as not to totally isolate the snug, we understand is still ongoing!
Finally
Downdraft problems in public houses or hotels are invariably caused by the kitchen extraction system no matter how may rooms away it is situated and is usually only cured by adding a chimney extract fan to the top of the flue.
