Each tank comes standard with one high-mount stainless steel heat exchanger with 3/4" connections for domestic hot water pre-heat. Any number of heat exchangers can be added to the tank to increase capacities or can be mounted high and low in the tank to perform a variety of functions like spa heating, closed loop radiant floor heating or even snow melting. Tanks also include tank level indicators, 10K sensors (one high and one low) in water tight dip tubes, a pump flange for a solar pump with fill and drain port and a passive vacuum breaker and condensate breather system for low maintenance. Tanks are lined with seamless EPDM and have a 20 year warranty against leaking. These tanks have an indefinite life expectancy and may be located outside.