Heater is a device that is used to provide warmth and comfort in indoor or outdoor environments. Heaters are available in a variety of types and sizes, and can be powered by electricity, natural gas, propane, or other fuel sources.The most common types of indoor heaters include electric heaters, gas heaters, and oil-filled heaters. Electric heaters use electricity to produce heat and are often portable and easy to use. Gas heaters use natural gas or propane to produce heat and are often used in homes with a central heating system. Oil-filled heaters use electricity to heat oil inside the unit, which in turn radiates heat into the surrounding space.