Armstrong model X19350L-21 all stainless steel plate and frame heat exchanger, equipped with (21) 10" x 34" plates for 50 square feet of surface area, 2.5" threaded pipe ports, rated to 150psi, part number 4X19GBN-21-027, serial number AN081002-101, national Board Number 5805, new in 2008, very good condition – as is.