Mueller Accu-Therm 111 sq. ft. stainless steel plate heat exchange. Model AT20 C-20. Maximum working pressure is 100 psi @ 150° F. Heat exchanger has a carbon steel 2" NPT and a 1.5" carbon steel NPT with a 1" reducer on top and a 2" NPT and a 1.5" NPT with a 1" reducer on the bottom. The maximum pack length for the plates is 6.51" and minimum is 6.29". Serial # G31503.