Enhanced tubular heat exchanger

A furnace comprising:

• a burner;
• a casing defining a plenum;
• a fan operably connected to said plenum;
• and
• at least one elongated tube disposed in said plenum, said tube including a flue portion, an enhanced portion, an inlet operably connected to said burner, and an outlet, said flue and enhanced portions defining a passageway for a flow of heated flue gases from said inlet to said outlet, said tube being in fluid flow communication with said fan, said flue portion located adjacent to said inlet and adapted to receive said heated flue gases, said enhanced portion comprising a substantial axial portion of said elongated tube, said enhanced portion located adjacent to said outlet, said enhanced portion being generally flattened relative to said flue portion and having a smaller cross-sectional area than the cross-sectional area of said flue portion.

A furnace comprising:

• a burner;
• a casing defining a plenum;
• an exhaust fan operatively associated with said plenum;
• a plurality of elongated tubes disposed in said plenum, each said tube including an inlet operably connected to said burner, an outlet operably connected to said exhaust fan, a flue heated flue gases from said burner, and an enhanced portion located adjacent to said outlet for expelling said heated flue gases, said enhanced portion comprising a substantial axial portion of said elongated tube, said enhanced portion being narrowed and having a smaller cross-sectional area than the cross sectional area of said flue portion, said flue portion and enhanced portion of each said tubes defining a communication passage for the flow of heated flue gases from said inlet to said outlet;
• and
• a circulation fan in communication with said plenum and arranged to cause a flow of air over said tubes in a first direction;
• at least one said enhanced portion having a cross-sectional elliptical shape which is disposed with the major axis defining a line which is generally parallel with said first direction.