Hot water from any heating boiler is circulated through the coil inside the tank to heat all the water in the tank. The HF-85-XHO, with an 85-gallon tank, and the HF-115-XH, with a 115-gallon tank, both offer high output coils. The large counter flow heating coils are designed to promote more condensing when connected to high efficiency mod-con boilers. Smooth wall coils are used to minimize lime and sediment collection. The units can be banked together for applications with high water heating demands. Coils can take 300K to 495K BTU/HR.