Gas appliance combustion systems

摘要

Required blower power in an induced draft combustion system is reduced by recovering pressure from dynamic energy of flow of combustion products. To this end, the outlet duct is diverged gradually, such as an included angle of less than fifteen degrees, and preferably at an angle of substantially seven degrees. Divergence of the outlet duct may be expressed in polar coordinates having a polar axis, overlapping radius vectors and a variable polar angle of such overlapping radius vectors relative to the polar axis. A difference between such overlapping radius vectors is increased in a direction of flow of the combustion products and the outlet duct is structured with cross-sections increasing incrementally in terms of the increasing difference between the overlapping radius vectors. Condensate may be drained from a combustion product by providing the duct with a lateral offset having a bottom extending at an angle to the earth's field of gravity. Condensate may be collected at that bottom, and the condensate may be drained from that bottom.