APV model SR6GLO-S plate and frame heat exchanger, with 16" x 50" plates, set up for (3) zones with (2) regen blocks, zone one: 22 plates – 120 square feet; zone two: 55 plates – 300 square feet; zone three: 16 plates – 88 square feet, 4" Tri-Clamp and threaded main ports, 3" threaded regen ports, stainless steel contact and frame construction, serial number 22669, good condition – as is.