Used 22 sq. ft. 304 Stainless Steel Heat Exchanger. Mfg. by Perry Products. Model #6-22FTSSX. Shell: 304 Stainless Steel, 85 psi @ 300 F. Tubes: 304 Stainless Steel 35 psi @ 300 F. 6" diameter x 5' tube length. (28) 5/8" OD x 18 GA tubes. Heads 304L Stainless Steel. 6'6" O.A.L. Serial# B-4623. National Board #4249. Built 1991.