A fan circulates air from inside the building over the warm heat exchanger. This warmed air is then circulated throughout the building. This process heats the building. In some buildings, forced hot air heating ducts are also used for cooling. Since heating ducts are best placed at floor level, and cooling ducts are best placed at ceiling level, the situation is far from optimal.
Pumps circulate the hot water through pipes in the building.
This heated water warms radiators placed in the rooms. These radiators, in turn, warm the air in the room. In some homes, pipes are buried in the concrete slab. This is type of system is called radiant heat. Hot water heat has made steam heat obsolete in homes and smaller buildings.