A high efficiency fuel-fired induced draft condensing furnace is provided with a horizontal vent termination assembly installed in an exterior wall of a building served by the furnace. The vent termination assembly, constructed entirely from PVC plastic pipe and fittings, includes a combustion gas vent pipe connected to the furnace's draft inducer fan outlet, horizontally extending through an opening in the wall, and having an open discharge end positioned outwardly beyond the wall. A larger diameter combustion air inlet pipe circumscribes the vent pipe within the wall opening and forms around the vent pipe an annular combustion air flow passage that is communicated with the furnace combustion air inlet. A coupling member connected to the outer end of the inlet pipe has a diametrically enlarged end portion positioned on the outside surface of the wall, axially inwardly of the outer vent pipe, and forming an annular inlet to the flow passage between the two pipes. The outer end of the vent pipe is left uncovered so as to permit direct, unimpeded axially outward discharge therefrom of furnace combustion gases. In a similar fashion, the enlarged end portion of the coupling member is left uncovered so as to permit direct, unimpeded axially inward entry therethrough of outside combustion air. Because the open outer ends of the concentric coupling and vent face in the same axial direction, the operating pressure differential across the furnace heat exchanger is substantially unaffected by changes in outside wind velocity and direction.
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