Tankless coils used on heating boilers: This device, basically a coil of finned copper tubing which is inserted into the heating boiler, is used to provide domestic hot water to some buildings
Tankless coil water heaters use a heating coil installed in the home's main heating system for water heating. Common in oil-fired boilers and some gas-fired boilers, tankless coil water heaters are an inefficient means of heating water. Seen primarily in colder climates, boilers are heating systems that use water or steam to distribute heat throughout the home.
Tankless coil water heaters use the heat from a home's boiler to heat water just when it is needed. This is accomplished by a coil of pipe, which is immersed in the boiler water, acting as a heat exchanger, passing heat from the boiler's hot water to the cold water being drawn through it. The big advantage of tankless coil systems over storage units is they have no stand-by heat lossessince water is heated only when needed
Burnham-America Tankless Heaters