Mid-efficiency furnace with multiple venting option

摘要

A multi-category gaseous fuel-fired heating apparatus having a combustion chamber, a mixing chamber in fluid communication with the combustion chamber, and an induced draft blower in fluid communication with the mixing chamber whereby combustion air is drawn into the combustion chamber for combustion of the gaseous fuel and the flue gases are drawn from the combustion chamber through the mixing chamber and exhausted into either a high temperature flue gas vent or a low temperature flue gas vent. The mixing chamber includes a dilution air inlet which, in a high temperature vent mode of operation of the heating apparatus is sealed off by an orifice plate disposed between the mixing chamber and the induced draft blower, and in a low temperature vent mode, the dilution air inlet is open and a larger blower inlet orifice is used.