A central heating boiler heats water using electricity, gas, heating oil or another fuel source, and then distributes hot water or steam to the rooms of the home. As the water or steam passes through the radiators, radiant heat warms the room.
The oldest central heating boilers create steam that moves without the aid of a pump through pipes to distribute heat through radiators into the room. Steam heating systems are less efficient than other types of heating systems available as of 2014, so they are less common in new construction.
Some hot water systems also operate without a pump. Hot water is less dense than cold water, so it rises through the pipes to distribute heat to the rooms. There are both open and closed gravity systems. Open systems have vents that allow excess pressure to escape while closed systems use expansion tanks. With these systems, owners often experience air locks, leading to uneven heating.
Hydronic heating systems use a motor-driven pump to distribute the hot water throughout the home. The addition of a pump provides more rapid heating of the living space. Moving the water through the system in this way reduces heat loss and improves heating efficiency.