In its crudest form, central heating originated in the first century in the Roman Empire. A central open fire would warm the air, which through natural air currents would travel through wall cavities, or ducts, into many rooms of the house. However advanced this system was in its time, it bears little resemblance to a present day system.
A basic modern day central heating system consists of three main components: boiler, pump and hot water cylinder, all linked together by copper pipe. The most common place to fit the boiler is in the kitchen. Cold water from the tank in the loft is fed into the boiler, where it is heated to around 60 degrees centigrade. The water is then circulated through all the radiators in the house, back into the boiler to be re-heated and then back through the radiators in a constant loop. A second circuit runs from the boiler up to the hot water cylinder (usually installed in an upstairs cupboard) and back to the boiler, again in a constant loop. The hot water cylinder then provides the water for all the hot taps throughout the house, plus washing machine and dishwasher if fitted.
The radiators are usually found in all rooms plus hallways and are shaped to give a large surface area which warms the air as it comes into contact with it. Modern radiators are made of pressed steel, although older types were made of cast iron and were extremely heavy. The water is pumped through the system by a water pump, which is electrically operated and often mounted close to either the boiler or hot water cylinder.
All this is connected together with copper pipe usually run under floorboards. A room thermostat is often fitted to regulate the temperature of the rooms by switching the pump on or off as required. A thermostat can also be fitted to the hot water cylinder to control the temperature of the hot water to the taps or faucets. The system is then controlled by a programmer, to give heat and hot water at various times of the day as and when required.
