Do you sometimes find that smoke comes out of your fireplace when you put a log on the fire? There could be several reasons for this and it doesn’t necessarily mean there is anything wrong with your wood burner. We’ll explain the various possible causes and what you can do to prevent smoke escaping into the room.
The chimney is the engine of the fireplace and it works as long as the air inside the chimney is warmer than the air outdoors. These conditions create a good updraft which draws the smoke from the fireplace through the flue and out the chimney. If the temperature inside the chimney is lower than the temperature outdoors, the air will move in the opposite direction and cause a downdraft. This can happen if there is a sudden, considerable change in the outdoor temperature. Other reasons could be windy conditions, negative pressure in the room, faults in the chimney, the length of the chimney, incorrect lighting method or poor quality firewood.
We call it back-puffing when smoke comes out of the fireplace while the door is open. We recommend opening the door slowly and cautiously to balance the pressure inside the wood burner when putting wood on the fire. If you open the door too quickly, smoke will be drawn into the room. If smoke continues to spill into the room despite opening the door slowly, there may be other reasons why this is happening. We explain these below.
New-builds are well insulated. This means that not much air enters except through the balanced ventilation system. If you are using a powerful extractor fan in the kitchen and/or are vacuum cleaning the room at the same time as you have a fire going in the fireplace, negative pressure (more air is drawn out of a space than is drawn in) may be created and there is a risk that the air flow in the chimney will be reversed and will push smoke out into the room. The solution might be to fit an anti-downdraft cowl on the chimney or a separate air intake next to the fireplace.
Fireplace back-puffing can also be caused by problems with the chimney, or gaps in flue pipe or masonry joints. If the flue is too narrow, not enough air and smoke will be able to pass through it even if it draws well.
Cracks in the flue can impair its ability to draw the smoke out.
The length of the chimney can also affect its ability to create an updraft. Chimney length clearly affects draft and if the chimney is too short the updraft may be insufficient or unstable.
If the draft is not working correctly for any of these reasons, we recommend you contact your local dealer to discuss what improvements can be made to the chimney.
In practice it should be easier to get a fire going when the outdoor temperature is low. When the hot air from the fireplace goes up the chimney and is replaced by cold air from outside, it creates a good draft in the chimney. If it is very windy, the direction of the wind can have a positive or negative effect on draft. It can either draw air up the flue more powerfully or blow down the chimney and create poor draft. A wind cap can solve this problem and is available from your local dealer.
Obviously, it is also important to follow proper burning practices, as incorrect burning can increase smoke and soot formation in the fireplace or wood burner. Remember to use dry, finely split firewood to build the kindling stack, have the air vent(s) open, and light the fire on the top of the stack. The wood burner will then reach its operating temperature more quickly and the smoke and gases are combusted.
