What is Hot Water Heating?

Hot water or steam in pipes is a convenient way of moving heat around buildings. This is what some central heating systems do. The water is heated up in a boiler and pumped through pipes to radiators in each room. Heat travels from the water into the metal of the radiators. Moving heat from one object to another in this way is called conduction.
Now the heat travels from the radiators to warm the air in the room.
It does this in two ways.
One is by a movement called convection. The radiator heats the air around it. The heated air rises and cool air rushes in to take its place. The hot air moves along the ceiling away from the radiator pushing cooler air in front of it. This convection current moves down the wall opposite the radiator, along the floor and so back to the radiator again.
The other way a radiator works is by sending out waves of heat in the same way as the sun. This is called radiant heat.

Hot air from the radiator moves around the room. The heat is gradually lost to the cool air by conduction.