Homes using forced air heat have a furnace that heats the air in it and a fan that blows the hot air into heating ducts that allow the hot air into the rooms. It rises and forces the colder air out of the room through return ducts, the entrance to which are usually near the floor. Hot water heat has pipes carrying hot water that have fins on them. The fins promote convection of air past the hot water pipe. This warmed air then circulates through the room. Electrical baseboard heat works in the same way. Electric resistance wiring in the floor or ceiling can warm the air in contact with these surfaces, again creating convection currents. Convection is the movement of thermal energy through a fluid (such as liquid or gas).