Heat Exchangers are manufactured from 316 stainless, with a specialty grade being used for the inner coil that has a rated working pressure of 10,000 PSI. The coil can be exchanged by removing 8 bolts. Size of heat exchanger is 4½" x 20". Other model has a stainless outer housing and stainless inner straight tubes. This model is less expensive, however, the inner assembly cannot be changed. All units are tested and meet specific quality control criteria before shipment.