Abstract: An improved furnace is provided which can be field modified to change the pressure drop across the inducer. The pressure drop is modified to accommodate vertical or horizontal venting and adequately lined and inadequately lined chimneys. A first rate of flow of combustion byproducts into the vent system is used when the chimney is adequately lined and a second relatively higher rate of flow is used when the chimney is inadequately lined. The rate of flow is changed by inserting or removing an obstruction in the flow of combustion byproducts. The obstruction could be a tab or choke placed at the inducer outlet or a similar device in the inducer inlet. When the tab is in place the flow of combustion byproducts is reduced. When the tab is removed, the flow rate increases. Alternatively, the inducer inlet could be adjusted to increase or decrease the amount of air flow through the inducer.

Abstract: A heating apparatus for delivering heated air to an enclosure comprising a casing with at least two compartments separated by a panel. A burner with an arcuate profile is located within a first compartment of the casing for burning a combustible fuel-air mixture delivered thereto and producing products of combustion. A heat exchanger is located within a second compartment of the casing and has an opposed inlet and outlet. The inlet is in fluid communication with the burner through an aperture in the panel. The heat exchanger receives the products of combustion. A blower is located within the casing for directing a flow of air across the heat exchanger into the enclosure. Through the heat exchanger heat is transferred from the products of combustion to the air. An exhaust system is in fluid communication with the outlet and includes a vent for exhausting the products of combustion from the casing. The vent is contained within the casing.

Abstract: In a two-stage furnace system, including a thermostat, at least one gas burner with a low and high-fire operating capability, an inducer fan having low and high speed operating settings, and a high-fire pressure switch, a method for handling the high-fire pressure switch being in an inappropriately open condition. The method has the steps of: determining whether the thermostat is issuing a call for high heat and, if it is, determining if the high-fire pressure switch is open. If the high-fire pressure switch is open, waiting a predetermined time, determining if the high-fire pressure switch is still open and, if it is, completing a furnace shutdown procedure, then initiating a normal shutdown, then an ignition sequence in high-speed inducer pre-purge mode, determining if the high-fire pressure switch remains open, and if so, running at least one gas burner in low-fire mode. If, while these steps are being performed, the high-fire pressure switch closes, running the system in high-fire mode.

Abstract: A two-stage induced draft furnace is operated at either high heat or low heat with the gas valve switched to high-fire or low-fire. High-fire and low-fire combustion pressure switches sense the collector box flue gas pressure and actuate respective solenoids of the gas valve. Under some conditions the inducer can produce sufficient negative pressure at low fire to prove the high fire pressure switch and cycle the burners on high fire. To prevent this, relay contacts are interposed between the high fire pressure switch and the gas valve solenoid to deny thermostat power to the high-fire solenoid whenever there is a call for low heat.

Abstract: A belled orifice inlet plate is provided for an induced draft combustion furnace heat exchanger of the type in which an inshot burner produces a hot gaseous combustion that is injected through an opening in the inlet plate into a combustion zone in the heat exchanger. The inlet plate has a flared collar that surrounds the opening at its periphery, and which extends a predetermined distance into the combustion zone. Preferably, the collar should have a depth on the order of one-quarter inch to one-half inch, and the flared portion should have a radius of curvature on the order of about one-quarter inch.