Patent ID: 8646442

Claim:
A clamshell heat exchanger for use in a gas-fired direct combustion furnace, comprising: a first clamshell half; and a second clamshell half that when joined with said first clamshell half forms a passageway having an inlet and an outlet, wherein said passageway includes a U-bend located between said inlet and said outlet, wherein said passageway includes a second U-bend between said U-bend and said outlet, said second U-bend located on an opposing side of said clamshell heat exchanger as said U-bend, and, a cross-sectional area of said passageway progressively narrows over substantially an entire length of said passageway between said U-bend and said second U-bend and further progressively narrows over substantially an entire length of said passageway between said second U-bend and said outlet.