<human>:  Explain the underlying principle behind central heating systems.
<bot>: The underlying principle behind central heating systems is that they use external sources of heat, such as natural gas, fuel oil, electric, or wood, to generate heat which is then distributed throughout a building using a series of pipes and vents. Central heating systems are typically comprised of a boiler which heats the water, a pump which circulates the hot water, an air handler which uses the heated water to warm the air, and thermostats which monitor and control the system. The end result is that the air in the building is warmed, providing a comfortable living space for people inside.