Elimination of Downdraught

Downdraught conditions on a conventional chimney/boiler house arrangement occur when the flue exit is subjected to a higher pressure than the air inlets to the boiler house, which are normally in the form of a louvered door.  This pressure differential will normally be overcome by extending the height of the conventional chimney to create the additional buoyancy necessary to overcome the downdraught problem.

With a Monodraught flue terminal the external flow pattern is always such, that the pressure at the top of the flue exit is less than the stagnation pressure which occurs at the windward side inlet.  No matter which way the wind is blowing, there will always be at least one air intake subject to wind pressure with the air ducts on the opposite side of the chimney system always acting as permanent ventilators to the boiler house.

The air inlet/ventilation ducts will be constantly changing according to wind conditions with the boiler house acting as the 'balancing chamber' to equalise these pressure variations at the head of the chimney.