What is a Room Heater

A furnace uses the energy of gas or oil to heat air.
But how does that hot air get where it's supposed to go?
How does it warm bathroom tiles and make bedrooms cosy?
Most heating systems make at least some use of convection, the circulating movement caused by differences in air temperature and pressure.
Old-fashioned gravity furnaces relied heavily on this phenomenon.
Supply ducts connected to the heat source let the air expand and rise through open registers and up stairways.
Cooler air naturally dropped down return ducts to the basement furnace.
This was a slow-moving and quite inefficient loop.
Modern forced-air systems use a fan that blows the hot air through ducts venting into each room.
But convection is important here, too. Ducts are open placed at the base of exterior walls, so hot air sweeps up along the wall and into the centre of the room; cold air drops and enters a return duct, often placed in a similar location on the opposite wall.