A STOVE is a common source of heat, consisting of an enclosed space in which fuel is burned to heat the surrounding air. It is usually five letters long. An IRE is a three letter word for a device that produces heat by burning fuel, such as coal or wood. A FURNACE is a seven letter word for a device that uses fuel or electricity to heat air or water, and is commonly used in homes. An electric blanket is a fifteen letter word for a device that uses electricity to generate heat, and is often used to keep people warm in bed. All of these terms refer to sources of heat.