Heat transfer coils, tailored to your system. Hubbell hot water heating coils efficiently transfer heat from a primary heat source to your potable domestic hot water system. The u tube heat exchanger transfers heat to the domestic water without direct contact to the primary heat source. Primary heat sources include steam, boiler water, solar water, or high temperature hot water (HTHW). Our heating coils are custom-built to your specs, with options available for any commercial or industrial application.