Tankless Coils from Boilers
Tankless coils are indirect water heaters that take their heat from the steam or hot water boiler that is used to heat the house. A cold-water supply pipe extends into the hottest part of the boiler water. The water in the copper tube is kept hot by the boiler water. When there is demand for hot water, water flows through the tube through the hot boiler water, and water is delivered to the fixture.
Highly recommend getting your boiler tuned up and cleaned yearly
some local recommendations https://www.geiler.com/