Hydronic towel warmers operate in conjunction with a closed loop forced-hot-water heating system and typically operate only during the period that the central heating system is operational. The hydronic towel radiator is heated by circulating warm water from a boiler, which typically operates from home heating oil, natural gas, or lpg propane depending on the boiler. Hydronic towel radiators are most often used as the main source of heat for a room (particularly bathrooms, kitchens, entryways and laundry rooms), and proper sizing is a priority. A good "rule of thumb" value for a room is 40+/- BTUH per square foot of floor area, assuming a single outside wall with one window, and a standard ceiling height. For a more accurate heat loss value, consult with a qualified heating specialist.