The Max-E-Therm heater uses a specially made Cupra Nickel Exchanger. Easy to install. Just hook up to your gas line and plug it in. Digital readout of pond temp and the set temp. Energy efficient with an industry rating of 84% efficiency Water enters in the top 2" union fitting circulates through the cupra nickel exchanger and back to the pond via the bottom 2" union fitting. Available in 3 sizes Please note: These are a special order item and not a stock item like most of our products.