Stainless Steel Tubes and Copper Fins The ultra-clean A31 series is appropriate for applications that employ deionized water The Cenden A31 Series Heat Exchanger couples an efficiency approaching that of our all-copper B21 design in a high-reliability 10.5" x 5.8" heat transfer area. Thermal capability ranges up to 75 Watts / ÂșC, depending on configuration. Each A31 Unit utilizes:Cenden's ...