How does central heating work?

The overwhelming majority of people in the UK have some type of central heating but a surprisingly large number don’t really know how their central heating system works. We’ve broken down the main components of central heating systems to help you fully understand how they work together to heat your home.

How do boilers work?

At its most basic level, a typical boiler works the same way as a gas stove in that it burns natural gas to produce heat. However, where they differ is that, when turned on, they have a constant stream of water running across a heat exchanger to continuously heat enough water to warm your home.

Traditional boilers would run this water through a pipe coiled through a hot water tank to heat (drinkable) water for domestic use, before feeding off to radiators. However, modern combi boilers only send this water to a secondary heat exchanger that quickly heats water as it comes from the mains.

What do boilers burn?

The majority of boilers run off natural gas which is often piped directly into your home. However, not everyone has access to the gas grid. There are several other options including those that run directly on electricity, oil boilers that use kerosene, LPG boilers that burn liquified petroleum gas, and even wood-burning boilers.

All these options have different efficiencies, prices, and carbon footprints which makes them suitable for all sorts of different installations.

How do radiators work?

Radiators work very simply. Water is heated from the boiler and travels to the radiator where it goes through internal pipes that twist back and forth inside the radiator to heat up the surrounding air. As hot air rises, the warm air circulates the room while cool air sinks until it moves near to the radiator where it is then heated.

A common misconception is that you can control how hot your radiator gets to control the heat of your room, but this isn’t actually true as there is only one temperature of water heading to your radiator from the boiler. The valve on the side of your radiator works by sensing the temperature of the room, turning the radiator on when it gets too cold and shutting it off again when the room heats up.

How do thermostats work?

Thermostats work similarly to the thermostatic valves on radiators but, instead of blocking and opening the supply of water to the radiators, it simply turns the boiler on or off. Modern thermostats are usually wireless and paired with a receiver that’s installed with your boiler. When the temperature of your home gets a little too cold, the thermostat will measure this and send a signal to the receiver in the boiler that will, in turn, tell the boiler that it’s time to turn on.

As you can imagine, thermostatic radiator valves and thermostats can work against each other as the thermostat can keep calling for heat but, if the thermostatic radiator valve in the room thinks it is warm enough, the room won’t heat up.

Despite being a simple idea, thermostats can be extremely effective at regulating the temperature of your home and saving you money on heating bills. While the temperature of your home will fluctuate around the set temperature as the boiler turns on and off, this is not normally noticeable.

Central heating water

The water in your central heating, and in your radiators, stays in your system indefinitely and isn’t connected to the hot water that comes out of your taps. This means that if the pressure keeps dropping – in a typical pressurised system – then you may well have a small leak. It also means that you can add chemical additives to your heating system to protect it from corrosion.

The water from your taps comes from the mains water supply and is either heated for temporary storage in a hot water tank or heated as it comes into your home for immediate use.

How does water move around your central heating?

Almost all modern homes will have pumped, pressurised systems and the pump that drives hot water around the central heating system is often an internal part of the boiler. These are referred to as fully pumped systems, however they are not the only type available.

Older installations may have gravity-fed designs which operate on the fact that hot water is less dense, and therefore lighter, than cold water. This means that as water is heated up by the boiler it can be pushed through the system by the weight of the cold water from a cold water tank in the attic. By the time the warm water reaches the cold water tank again, it will be sufficiently cool and heavy to push down on the warm water and continue the cycle.

The final type is combined systems that use both pumps and gravity to move water around the pipes.

Other central heating types

Warm air systems are popular in North America and commercial buildings in the UK, although they’re not common in British homes. This type of system work by heating air rather than water in a central boiler which is then fed through ducts into rooms that require heat. The advantage of these systems is that they can be integrated with air conditioning systems.

Heat pumps work in exactly the same way as your fridge, except that instead of drawing heat out of your fridge-freezer, they draw heat out of the ground and into your home. This can then be pumped directly around your home to radiators or underfloor heating similarly to more common central heating systems.

While not strictly ‘central’ heating, storage heaters are a popular option for those living off the gas grid. These are electric heaters that store the heat they generate. This means that they can heat up during the night when electricity is cheaper and then release that heat during the day when electricity is more expensive. Aside from this, they function much like normal radiators – except without the need for any plumbing.