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.