Abstract: A furnace is adapted for operation in downflow, left horizontal flow and right horizontal flow positions. The furnace includes plural burners, a two-stage heat exchanger, a header box at the heat exchanger outlet for collecting products of combustion from the heat exchanger, and an inducer for inducing a flow of products of combustion through the heat exchanger. A condensate drain and trap are also provided for draining condensation from the header box and from an exhaust vent through which products of combustion are exhausted from the furnace. In accordance with one feature of the invention, a manifold is located inside the header box to divide the header box into first and second chambers. A pressure sensor senses differential fluid pressure between the first and second chambers for detecting a blocked condensate drain condition.

Abstract: A furnace includes a generally cylindrical combustion chamber that is open at one end for receiving a single port inshot target burner. The combustion chamber is connected to a heat exchanger through which the combustion products are drawn by an induced draft blower. A flame retention ring is provided in the target burner to aid the flame in attaching to the outer surface of the flame retention ring and thereby improve flame lifting characteristics. Also, a frustro-conical member surrounds the end of the target burner within the combustion chamber for directing air into the combustion zone to enhance the combustion process.