Types of Boiler Explained

different types of boilerWhen it comes to choosing a new boiler or central heating system for your home, there are plenty of considerations to make before going ahead with an installation. Not only is the type of boiler itself important, but you also need to think about the central heating system as a whole and the type of fuel you want to use to power your home.

A central heating system needs to be adequate for your home’s needs, without being oversized as this can lead to wasted energy (and of course money). You should consider things like the number of occupants in your property, if you will need to use multiple showers or taps at once and the kind of space available. Our guide covers the three most common types of boiler and central heating options; system boilers, conventional boilers and combi boilers. Any new gas boiler you have installed will be a condensing boiler model. This is because government legislation states that all new gas-central heating boilers must be a high efficiency condensing boiler.

Fuel type is another big consideration you will need to make when it comes to choosing your home’s new heating system. There are plenty of factors that can affect your decision, including your home’s connection to gas & power grids, if you want to use renewable energy sources and the kind of space and setup of your property itself. Our guide covers the most common fuel sources used in the UK – gas, electricity, oil and solid fuel.
Got a certain boiler type in mind? Use the list of links below to navigate to the relevant part of this guide:

Condensing Boiler
Combi Boilers
System Boilers
Conventional Boilers
Gas Boilers
Electric Boilers
Oil Fired Boilers
Solid Fuel Boilers

For more information on older boiler types including back boilers, wall mounted and free standing systems, visit our guide to other types of central heating boilers.

Condensing Boilers

condensing type of boilerCondensing boilers typically extract over 90% of the heat from the fuel they burn, making them both cost effective and energy efficient. They are so effective because they extract heat from flue gases which would have otherwise been lost by a non-condensing boiler. For this reason any new boiler installed in the UK (from 2005) has to be condensing whether it’s combi, system or conventional.

Condensing boilers were not overly popular when they first hit the market, with early teething problems and a collection of myths about their reliability putting many homeowners off. Since then condensing boilers have come a long way and many of those old issue have been resolved.

 

Advantages of a condensing boiler

Energy efficient and cost effective
Thanks to the fact that they are over 90% efficient, condensing boilers offer great value for money over time and also have less of a negative impact on the environment that older boiler types. Whilst they can be a little more expensive to purchase, the fact that they are more efficient should outweigh this.

Compact design
If you opt for a condensing combi boiler there is no need for water storage tanks, making it ideal for a smaller property. The size of the boiler itself can also be much more compact and modern in design than many older models.

Disadvantages of a condensing boiler

Frozen pipes
In extremely cold weather there is a possibility that the condensate pipe, which leads from your boiler to the outside of your property, can freeze. Whilst this is easy to remedy with warm water, it can cause the boiler to stop working and possible cause damage to the system.

Costly maintenance
Condensing boilers are more complex than some of the older boiler types and therefore maintenance can be a little more costly. The best way to avoid major boiler problems is to have your boiler serviced annually by a Gas Safe registered engineer, to ensure any issues (or potential issues) can be dealt with.

Visit our guide to condensing boilers for more information

Combi Boilers

combi boiler typesA combi boiler, also known as a combination boiler, is a type of condensing boiler. Combi boilers are highly efficient and compact, making them ideal for smaller homes. The name combi comes from the fact that these boilers are able to act as both a water heater and also a central heating unit. Thanks to their space saving features, combi boilers are one of the most popular choices in the UK – accounting for over half of domestic boiler installations each year.

Combi boilers work by heating water directly from the mains, so you don’t need a hot water storage cylinder or cold water tank. This is ideal for smaller properties without airing cupboard or roof space. This heating method also makes them very energy efficient and affordable to run, as water is not heated and stored (and thus wasted if it’s not used). Whilst combi boilers have some great advantages, there are also considerations you should make before going ahead with an installation.

 

Advantages of a combi boiler

Compact
Combi boilers are ideal for small homes as they require no bulky water storage tanks, they also require less pipework.

Energy and cost efficient
Since you only heat the water you need, when you need it, a combi boiler wastes very little energy (and therefore money).

Good water pressure
Providing you have an adequate level of mains pressure, you should experience a good level of pressure from your shower and taps with a combi boiler.

Quick, easy and generally cheap to install
Since a combi boiler requires no tank, it is one of the more straightforward boiler types to install. This also means it tends to be a cheaper option both for installation and repairs.

Hot water on demand
You don’t need to wait for a water tank to heat up as a combi boiler heats water on demand. This also means you can have an unlimited amount of hot water.

Disadvantages of a combi boiler

Requires a good level of mains pressure
It’s important to make sure that your mains supply can deliver an adequate flow rate and pressure before choosing a combi boiler. If not, it may not be the best type of boiler for your household.

Not compatible with all types of shower
You cannot use a power shower with a combi boiler, as the pressure is dictated by that of the mains supply.

Can’t run more than one shower or bath at a time
With a combi boiler you cannot run more than one shower or bath at a time (or run a hot tap at the same time). This makes it a less ideal option for larger households with multiple bathrooms.

No backup water heater
As there is no immersion heater, if your combi boiler breaks down you will not have a backup supply of hot water.

Visit our guide to combi boilers for more information

System Boilers

gas system boilerA system boiler directly heats your central heating and also produces hot water for your storage cylinder. It is a heat only boiler and works in a similar way to a regular boiler, however it includes additional units within the boiler itself such as an expansion vessel and a pressure release valve.

A hot water storage tank will always be required with a system boiler, as it needs somewhere to store the water it has heated. A system boiler doesn’t however require a cold water tank, saving space and making them more suitable for smaller homes than a conventional boiler.

 

Advantages of a system boiler

Fairly straightforward to install
Many of the components needed for a heating system are already built into a system boiler. This makes it more straightforward to install than some other boiler types.

You can use multiple taps at once
The storage tank means that you can get hot water from multiple sources like taps and showers at the same time without losing water pressure or seeing a temperature drop.

Doesn’t need a cold water feed tank
A system boiler doesn’t require a cold water feed tank, which would usually be located in a loft. This makes it ideal for smaller homes or those without attic space.

Compatible with solar thermal
System boilers can work with a solar thermal system, which uses the sun’s energy to heat water for your home. This can reduce your household’s carbon emissions and energy bills.

Disadvantages of a system boiler

Not compact
Unlike a combi boiler, a system boiler requires a hot water storage tank, making it far less compact.

Hot water tank heat loss
Any hot water created will be kept in a hot water storage tank until it’s needed. During this time heat will be lost, so it’s important to try and prevent as much of this heat loss as possible by insulating it.

You are limited by the size of your hot water tank

With a system boiler you can only use as much hot water as your storage tank can hold. If you require more you must then wait for your boiler to heat it again, and this is usually on a set timer.

Visit our guide to system boilers for more information

Conventional Boilers

Regular conventional boilerAlso known as a regular boiler, a conventional boiler system is made up of a number of parts including a boiler, heating controls, a hot water cylinder, a cold water storage cistern plus a feed and expansion cistern. A conventional boiler can often be found in older, larger homes and less are being installed as time goes by.

A conventional boiler system is fed by two tanks which are located in the loft. One of these, the cold water storage tank, draws cold water from the mains supply. The other is the feed and expansion tank, which feeds the boiler system and manages any water that expands in the system after being heated.

 

Advantages of a conventional boiler

You can use multiple taps at once
Since the water comes from a water cylinder, you can use multiple sources such as taps and showers, without experiencing any effect on water pressure or temperature.

Works well when replacing an older system
When it comes to replacing the heating system in an older property, a conventional boiler can be a good option as it requires minimal changes to the pipework if any.

It can work with a backup immersion heater
An electrical immersion heater can be installed into the hot water cylinder, so if your boiler breaks down you have an alternative way to heat water.

Compatible with solar thermal
A conventional boiler system is compatible with solar thermal panels, which harness the suns energy to create warm water which is then fed into your central heating system.

Disadvantages of a conventional boiler

Takes up a large amount of space
A condensing boiler requires both a loft and an airing cupboard to house the cylinders and systems that make it up. This means it is often not ideal for smaller homes.

Hot water tank heat loss
A conventional boiler system uses a hot water storage cylinder. Whilst hot water is stored in there it will lose heat over time, in order to prevent this you should insulate your tank well.

You can’t have instant hot water
Once you’ve used all of the hot water in your storage cylinder, you will need to wait for the boiler to heat another tank full before you can use more. This means you should consider the amount you are likely to use when choosing a water cylinder.

Complicated to install
Due to all of its separate parts and pipework, a conventional boiler system is one of the more time consuming and costly heating systems to install.

 
Get free boiler quotes
 

Gas Boilers

Types of gas boilerGas is the most common heating fuel type in the UK and the majority of homeowners who are connected to the gas grid opt for a gas boiler. There are 3 main types of gas boiler: regular, combi and system. Any new gas boiler installed (since 2005) must be a condensing boiler according to government legislation.

 

Advantages of a gas boiler

Cheaper to run than electric boilers
Gas is around 3-4 times cheaper than electricity per kWh making it a much more economical option when it comes to heating your home. Whilst a gas boiler is not 100% efficient (and an electric radiator is), you can still get more heat for your money from gas.

Gas is the cleanest fossil fuel
Whilst gas is a fossil fuel and therefore not environmentally friendly, it is the cleanest fossil fuel of those available. In fact, gas creates less than half of the CO2 emissions of oil, and a third of those produced by coal.

Disadvantages of a gas boiler

You must be connected to the gas grid
In order to power a boiler with natural gas you must be connected to the gas network. It can be extremely costly to have your property connected to the grid if it is not already, so if this is the case you may want to opt for a different fuel type.

Visit our guide to gas boilers for more information

Electric Boilers

types of electric boilerAn electric central heating boiler is a great option for anyone looking for a compact boiler for a smaller household. They are also a good alternative for homes that cannot install a gas boiler since they are not connected to a gas line.

A typical electric boiler will work by heating the water that runs through it with a heating element and this hot water is then pumped to where it is needed. Thanks to the way they heat water, electric boilers are considered one of the least wasteful options as there is extremely minimal heat loss like there is with a gas boiler.

 

Advantages of an electric boiler

High efficiency
An electric boiler can run at around 99% efficiency as it doesn’t lose heat in the same way as a gas boiler would. Whilst this does mean that the boiler itself is more efficient, it doesn’t necessarily make an electric boiler eco-friendly.

Simple, compact and often cheaper to install
Electric boilers use fairly simple technology when compared to a gas boiler. For this reason they are usually compact and in many cases cheaper to install than other boiler types, especially as there is no flue to be fitted. Since they don’t use gas, there isn’t the same risk present from carbon monoxide and you don’t need to use a Gas Safe Registered installer.

No need for a gas supply
For anyone without access to a gas line an electric boiler can be the ideal solution for heating a property effectively. Connecting your home to the gas line can be extremely expensive, so many homeowners opt for an electric boiler instead.

Disadvantages of an electric boiler

High cost of electricity
Despite being so efficient, electric boilers can be expensive to run due to the high cost of electricity. With gas costing less than half of the price of electricity, you should consider this factor before opting for an electric boiler.

Not always ideal for large properties
An electric boiler can only heat small amounts of water at a time, and usually they cannot store it for later use. This means a larger property which uses a lot of hot water, or has multiple bathrooms being used at once may not find an electric boiler adequate.

Reliance on electricity
Since this style of boiler runs on electricity, it might not be the best option for a property that is affected by power cuts or outages on a regular basis.

Visit our guide to electric boilers for more information

Oil Fired Boilers

Oil fired boiler typesA central heating system powered by an oil boiler works in a similar way to a gas system. An oil-fired boiler heats water, which then provides warmth for your home through radiators and hot water through taps.

Many homes that use an oil boiler choose to do so because they have no connection to the gas line, however there are a lot of considerations you should make before going ahead with this type of system.

 

Advantages of an oil fired boiler

No need for a gas supply
If your property is not connected to a gas line, using an oil fired boiler can be one of the most cost effective alternatives. It is however more expensive than using gas to heat your home, so if you have access to gas it maybe be worth considering that option also.

Disadvantages of an oil fired boiler

You can run out of oil
The fuel required for an oil boiler is not available on demand as it is with gas or electricity, it instead must be ordered and then stored in a tank. You will need to monitor the amount of fuel you have left and order it as needed.

Oil may have to be paid for in bulk
Ordering oil for your system can also present financial issues as some suppliers will require payment on delivery (as opposed to spread monthly).

Storage space for an oil tank
Oil tanks can in fact be sunk into the ground to save space, however if you opt to store it at ground level you will need to make a few considerations. This includes ensuring there is a level, non-combustible solid base for it to sit on, which can take up a great deal of space.

Visit our guide to oil boilers for more information

Solid Fuel Boilers

solid fuel boilerA solid fuel boiler provides an alternative option to a traditional gas or electric boiler. It works in a similar way, usually utilising the same kind of pipes and radiators, however the main difference is the fuel.

Solid fuel comes in multiple forms including pellets, coal and wood. These are burnt to heat up a tank of hot water, which is then used to heat your home and provide hot water.

 

Advantages of solid fuel boilers

Can be more environmentally friendly than other fuels
Certain fuels used by solid fuel boilers are actually considered carbon neutral, making them much more environmentally friendly than traditional boilers. This includes wood, as it actually releases around the same amount of carbon monoxide when burnt as it absorbs when it’s growing. If you use locally sourced solid fuel this will reduce the carbon needed to transport it, making it greener.

No reliance on gas or electricity
Having independence from gas and electricity means you won’t be affected by any price rises from suppliers.

You may qualify for the Renewable Heat Incentive
Some solid fuel boilers are eligible to receive the government’s Renewable Heat Incentive (RHI), a series of quarterly payments received over serval years. This scheme is administered by Ofgem, so it’s worth checking their website for the most up to date information about tariffs, eligibility and news to ensure a solid fuel system you install will be eligible.

Disadvantages of solid fuel boilers

Installation costs can be high
A solid fuel boiler can be very costly (depending on the type you opt for) when compared to something like a condensing boiler. There is also a range of other costs you may want to factor in for the life of your solid fuel boiler, including the delivery costs of fuel and any electricity used to power the system.

You need to remember to buy the fuel
A solid fuel boiler can run on a range of fuel types, but you will need to ensure they are suitable for use (for example you cannot just burn household waste). This means it’s important to make sure you have a reserve of fuel to use at all times.

Storage space
Not only will you need to purchase the fuel regularly, you will also need a reasonably large amount of storage space for it. It can take a lot of wood, or other solid fuel, to heat your property well so make sure to consider the need for additional storage space.

Visit our guide to solid fuel boilers for more information

Get your FREE Boiler Buyer's Guide now!

Top tips and tricks to getting the best boiler
replacement deal
Top tips and tricks to getting the best boiler replacement deal

Find local, recommended boiler & heating engineers

Start your quote

Find local, recommended boiler & heating engineers