Central heating systems have transformed the way we live, supplying us with the heat and hot water that make our homes much more comfortable to live in. But as energy prices become more volatile, how do you identify what type you have, how it works and what other systems are there?
What types of central heating systems are available?
One thing common to all central heating systems is that they deliver warmth to your home from a single, central source. Beyond this, central heating options can broadly be categorised into three major types:
Wet systems: these heat your home using water, which passes through a boiler or heat exchanger to your radiators.
Warm air systems: these draw in air from outside, heat it using a variety of technologies (such as gas or heat pump) and then circulate the warm air through your property using ducts, grills or vents.
Storage heaters: electric heaters designed to warm up during cheap periods of electricity (typically overnight) before releasing the heat during the day.
How does a wet central heating system work?
Wet systems work by circulating hot water through a system of pipes that connect to the radiators throughout a house. A boiler or heat exchanger sits at the heart of this system heating the water that feeds the network of pipes. Boilers burn fuel to heat the water – typically gas – and this kind of ‘wet system’ is the most popular form of heating system in the UK.
Despite their name, radiators don’t simply give up radiant heat; in fact, most of their heat is delivered through a process called ‘convection’, where air warmed by the radiator naturally rises, with cool air falling relative to it. As a result, the space in a room is heated by the circulating warm air.
The pipework connecting radiators to each other may also be connected to a hot water cylinder (tank), which will provide a supply of hot water for bathing and washing.
What types of wet heating system are available?
There are three broad types: conventional heating systems, combi systems, and pressure systems:
Conventional heating systems
This type is the most common in older homes, and usually makes use of gravity to feed hot water through the system to maintain good water pressure. This requires the hot water cylinder to be placed higher up in your home – at least on the first floor and sometimes in the attic – than the boiler itself. They’re not as efficient as combi systems at heating hot water.
Pressurised systems
Mains water is heated directly through a water cylinder – extremely efficient, but systems are expensive to fit and maintain, and require high mains pressure to work properly. On the upside, they allow you to feed hot water to multiple appliances simultaneously without the pressure temporarily dropping.
Combi systems
These are the most efficient system because they only heat water when it’s used. Combi systems remove the need for any kind of water storage tank, and are often smaller than regular boilers, freeing up a lot of space in your home. Although they’re able to maintain the mains water pressure for the heated water, they’re limited by the amount of hot water that can be produced at any one time.
Because of this, while combi systems are fast becoming the standard for new installations in smaller properties, they’re less suited to larger properties where competing demands are likely to be more frequent (for example, in a home with two bathrooms). Such demands result in poor flow when two or more people attempt to use the hot water simultaneously.
What types of gas boiler are there?
There are four types of boiler that use gas to heat your hot water and home. They are:
Combi boiler: designed to provide both hot water on demand as well as central heating. Instead of heating hot water in advance and storing it in a cylinder, combi boilers simply heat the water when you turn the hot tap or shower on. This is more efficient than heating first and storing later.
System boiler: provides hot water via a hot water tank, which is where the water is stored after being heated in advance of using it. Its primary advantage over combi boilers is that it’s better suited for larger homes as it can provide a constant supply of hot water from multiple outlets.
Regular boiler: also known as a conventional boiler, they require both a hot water tank and also a cold-water (or header) tank in the loft. Best utilised in places where the water pressure is low, as the gravity-fed system compensates for lack of water flow.
Back boilers: these are increasingly rare as they’re very inefficient. They offer both heating and hot water and are usually installed behind a fireplace.
What’s the difference between a condensing and non-condensing boiler?
Condensing boilers are more efficient than non-condensing models because they’re able to capture condensation from the heating process and recover some of the lost heat from waste gases to achieve efficiency rates of over 90%. Since 2005, only condensing boilers have been available for sale in the UK, so whether you have a regular, system or combi boiler, it’s almost certainly a condensing model.
What type of fuel is used in a boiler?
The most common fuel used in boilers is natural gas, followed by heating oil and, less frequently, liquid petroleum gas (LPG). Some boilers still burn coal (usually in the form of coal pellets) or biomass (usually in the form of wood chips). Electric central heating boilers are also available, whereby the water is warmed using an electric element.
New gas (and oil) boilers are required to be around 90% efficiency or higher (an A or B energy efficiency rating) and generally use condensing technology to achieve this. If your boiler is more than 15 years old, you may want to consider replacing it with a new energy-efficient one.
My home is heated via a district heating system, how does this work?
In some areas, notably parts of Nottingham and Sheffield, a centralised district heating source – or heat network – will deliver hot water to a number of homes simultaneously via a series of underground pipes. This removes the need for a domestic boiler and the mains hot water circulates around the pipes within the home to provide heating and hot water. The attraction of this type of system is its energy efficiency and low carbon footprint, translating into lower energy bills for the consumer too.
I've heard that ground source heat pumps are environmentally friendly, but will they lower my energy bills?
A ground source heat pump works along the same principle as fridges and air conditioning systems: cooling one area by making another hotter. In the case of a fridge or freezer, the air inside is cooled by expelling warm air; obviously heat pumps apply this principle in reverse.
Ground source heat pumps, powered by electricity, work by making the earth outside a home colder, by running a refrigerant fluid through pipes that are buried in a trench or a borehole, while delivering warmth to the heat exchanger indoors. That heat is transferred to the water running through the pipes inside a house to warm radiators and provide hot water.
Ground source heat pumps typically reach temperatures of around 50°C, which is significantly lower than a gas boiler, which can reach temperatures up to 90°C (although it's recommended that you set the temperature lower than this). This means the heat pump must run for longer to achieve the same level of comfort. Another consideration is that it tends to work better with underfloor heating rather than radiators as less heat is lost.
Although much more expensive to install, they can be as cheap to run as gas central heating and may be a good option if you live off the gas network.
How does a warm air system work?
Warm air systems are less common than other forms of heating in the UK – they were sometimes installed during the 1960s and 1970s but remain popular in North America. Air is heated by a boiler, typically fuelled with natural gas, and fed via ducts to rooms around the home. The warm air enters the room via a floor or wall vent.
In commercial buildings, variations on warm air systems are still in widespread use, although they typically also serve as a cooling (air conditioning) system.
In most homes, warm air systems have been replaced with 'wet' systems, which are generally more comfortable and efficient.
How does a storage heating system work?
The principle of a storage heater is that it contains bricks capable of storing large amounts of heat. These take advantage of off-peak electricity prices delivered by the likes of Economy 7 and Economy 10 tariffs to recharge their heat (Economy 10 may offer a short period during the day for recharging too). The stored heat is then gradually released the following day.
Storage heating systems, although consisting primarily of individual storage heaters, typically rely on a separate wiring system within the home for cheaper off-peak electricity, so can still to some extent be described as a 'centralised' system. The same wiring typically will also be used to heat a hot water cistern (tank).
A storage heater normally has at least two controls: one regulates how much electricity is used to determine how much heat is generated for storage, and the other controls how much heat is released. This means that if you're out during the day, you can delay the heat’s release until you return in the evening. More advanced storage heaters also have thermostatic controls.
Older storage heaters took up a lot of space, but modern models are far more streamlined through the use of bricks with much greater storage capabilities.
In some cases, storage heaters can also serve as direct electric heaters, providing heat directly from your electricity supply without going through the storage stage. Typically, they will use peak rate electricity for this. Often homes that rely on storage heaters will also have separate electric heating systems to supplement heating needs; again peak-rate electricity is used to top up in this way.
Electric central heating vs gas central heating
Which of the two should you opt for? We take a quick look at the pros and cons.
Electric central heating
The main benefit of installing electric central heating is that it’s available to homes not connected to the gas grid. In addition, electric night storage heaters are easier to install than gas central heating apparatus, mainly because they require fewer parts.
In the past, electric heating was considered more suitable for smaller spaces, but newer models are increasingly adept at handling larger properties as well. They’re also easier and cheaper to maintain thanks to fewer parts and digital-friendly interfaces; they’re also relatively silent.
On the other hand, electric central heating is usually more expensive as electricity unit prices are up to four times more costly than gas – even though 100% of the electric is used for heat (unlike gas, some of which gets wasted). On top of this, electric central heating storage heaters do not provide instant control. This means you must plan your heating needs ahead as switching the heating on at night means you may not be able to use it the following day.
Gas central heating
The main advantage of gas central heating is that it is cheaper, per unit, than electricity. On top of this, gas boilers are becoming increasingly efficient. Replacing an old boiler with a new energy-efficient model is pretty straightforward in terms of the installation process. Find out more on how to get a new boiler.
However, gas central heating isn’t without its own problems. Gas prices continue to rise, and although they remain lower per unit than electricity costs, they’re far from cheap. Another issue is if your home isn’t connected to the gas grid – getting connected can prove both lengthy and costly. Gas central heating boilers should also be serviced regularly to ensure they are in good working order.
Finally, as the UK transitions to Net Zero, gas boilers could find themselves banned as soon as 2025, although it’s likely this date will be pushed back. When that happens, you’ll need to consider other forms of heating, from electric storage heaters to air or ground source heat pumps.
FAQs
What is central heating?
Central heating systems are designed to deliver warmth to all the rooms in your property from a single source.
What types of central heating systems are there?
There are three main types: wet-based systems, which heat water, warm air systems, which draw air in from outside to be heated up and circulated; and storage heaters, which create stored heat during the night to be released during the day.
Are storage heaters central heating?
Technically no, as each heater can be installed and used independently. However, most storage heater systems are configured in such a way as to be controlled from a central source.
How do central heating systems work?
That depends on the system. Wet-based systems heat up water, which is distributed to radiators throughout the home that subsequently releases heat into the air using a process called convection.
What is a power flush of central heating systems?
A power flush is a specialist cleaning process designed to rid your central heating system – including the pipes, boiler and radiator – of any sludge, dirt, debris or rust that may have built up. Doing so increases your heating system’s efficiency and helps maintain your system. A power flush can take anywhere from eight hours to two days to complete.
What’s the difference between a combi boiler and a conventional or system boiler?
The key difference is that combi boilers provide instant hot water. They have the advantage of freeing up space in a home, because there's no need for a hot water cylinder (tank) like there is with a system or regular boiler.
In most cases, heating water instantly is more energy-efficient than 'stored' hot water systems. However, the hot water flow is slower than if it was coming from a cylinder. This is why combi boilers are more suited to smaller properties, where demand for hot water is less. Note that some combi boiler systems do support heating water in a cylinder.
Modern boilers generally no longer require tanks in the loft to 'pressurise' the system through gravity. Instead, they are sealed systems, and typically only require manual topping up from the mains water supply when the internal pressure has dropped (usually because of tiny leaks). This is a simple process that just involves opening a valve on a pipe below the boiler.
