Downdraughts An occasional burst of smoke apparently blown back down the chimney, particularly in high winds, may be the result of downdraught. A downdraught is caused by pressure at the top of the chimney being greater than that in the room where the fire is. It generally means that the top of your chimney is being "overshadowed" by some other structure nearby –such as the top of the roof; or something is causing the pressure at the bottom of the chimney to fall – usually an exposed chimney on the outside of an old house, into which the cold wind has found a way where, for example, the brickwork has become porous. First, check the top of the chimney. Is it well above any nearby structure such as the ridge of the roof (where "well above" means 0.6m if the chimney is less than 0.6m from the ridge and 1m or more if it is further away)? Are there other tall structures – buildings or trees – close by that might be interfering with the airflow? Can you do anything about any such interference? If not, a solution might be to increase the height of the chimney. Contact the experts. If you are satisfied that the top of the chimney is not being "overshadowed", look instead at its situation. How exposed is it (is it, for example, facing the prevailing wind)? What is the state of the brickwork and mortar – might cold draughts be getting through into the flue somewhere? Are there grilles and vents into the chimney that might be affecting the updraught? In a new chimney, simply heating up the flue may solve the problem. In an old chimney, you may require a liner. If you think this is the problem, Contact the experts. • Links to Isokern and perhaps other flue lining companies. Back to chimney problems