Abstract: A condensing mode furnace fired by a gun-type, power fluid fuel burner, such as an oil or gas burner, as a heat exchanger with a combustion chamber therein and communicating therewith. A duct carries the products of combustion from the heat exchanger to a thin and tube type condenser. An exhaust vent carries the products of combustion and condensate from the condenser, a drain line removing the condensate from the exhaust vent. A blower in the exhaust vent causes a flow of the products of combustion from the heat exchanger through the condenser and exhaust vent. An air passage surrounds the heat exchanger and condenser and a blower causes a flow of air serially over the condenser and heat exchanger to a hot air outlet. The furnace control initiates operation of the vent blower in response to a thermostat calling for heat in advance of operation of the burner thereby to purge on burned gases from the combustion chamber and heat exchanger.

Abstract: A gas-fired, condensing mode, hot air furnace has an exhaust passage for carrying the products of combustion from a gas burner to an exhaust flue. A heat exchanger is provided in the exhaust passage for extracting heat from the products of combustion. An air passage is provided for carrying a flow of air over the heat exchanger and a blower causes a flow of air through the air passage. The gas burner is enclosed and fires into the heat exchanger. A fresh air duct communicates with the burner enclosure for admitting fresh air thereto. A condenser is provided in the exhaust passage for removing water from the products of combustion, the condenser being exposed to the air passage. A second blower is provided in the exhaust passage for causing fluid flow therein from the fresh air inlet duct through the enclosure and the exhaust passage to the exhaust flue.