Reznor's EEDU indoor duct furnaces, with 80% thermal efficiency, were developed to provide an annual fuel use improvement of up to 25% when compared with gravity-vented duct furnaces. The use of a factory-installed power venter, with metered combustion air, limits burner flue losses while reducing the required vent pipe size. A sealed vent product collection chamber, in lieu of a draft diverter, reduces the loss of dilution air from the room in both the on and off cycles.