With Two Heat Exchangers

Horizontal stainless steel cylinders with two removable heat exchangers are triple energy. One heat exchanger usually takes the lower-temperature source, such as solar collectors or a heat pump, and the other the boiler that tops up; the electric element remains as backup.

For a hotel or clinic with a solar field and a boiler room, this means one stainless steel vessel instead of two. Each heat exchanger comes out separately through its own flange for cleaning.