Need help choosing which boiler is best for your home? The first step is choosing your boiler type. Learn more about combi, condensing, conventional boilers and more, then use our comparison tool to choose the best boiler for your needs.
Condensing boilers
Condensing boilers aren't strictly a boiler type but are an attribute common to all modern gas boilers – in other words, you can have a condensing combi boiler or a condensing conventional boiler.
Condensing boilers are extremely energy efficient because they capture and reuse some of the heat that would otherwise escape from the flue of a non-condensing boiler. This means they extract more heat from the same amount of fuel to save you money on your heating bills.
Combi boilers
What is a combi boiler?
Combination – or combi – boilers are the most popular kind in the UK and provide heat and hot water with no need for water tanks or cylinders. You can pick either a gas or electric combi boiler.
How does a combi boiler work?
A combi boiler includes everything required to provide both hot water on demand and heat your home in a single unit. Water is heated instantly using a metallic heat exchanger, which is triggered whenever you open a hot tap or take a hot shower.
Efficiency
Heating hot water on demand without having to store it makes the combi boiler the most efficient of all gas boilers on the market.
Cost
According to the latest UK boiler statistics, the price (including fitting) of a combi boiler can range from as little as £1,500 for a small, budget boiler to around £3,500 for a larger, premium model. Standalone boilers cost from under £600 to around £2,000 without fitting.
Pros
You get unlimited heat and hot water when you need it
There's no need for a tank in your loft
They don't take up much space
Virtually all components are built into the boiler, so more is covered by your boiler warranty
Popularity means Gas Safe registered engineers are easy to find
Cons
The water pressure could be reduced if you need hot water from more than one tap at a time
Combi boiler installation is quite tricky
Combining all parts into the boiler means there may be greater scope for things to go wrong
Combi boilers are suitable for almost any home, but best for smaller dwellings where several people aren't likely to need a lot of hot water at the same time. For those that do, a combi-storage boiler might be a good choice – as its name implies, it combines a combi boiler with a built-in hot water cylinder that stores relatively small amounts of water to help with greater demand. However, its storage is relatively small – consider a system boiler instead.
System boilers
What is a system boiler?
System boilers - also known as sealed system boilers - come with a water cylinder (which usually sits in an airing cupboard) and no water tank.
How does it work?
System boilers supply hot water both to your central heating and a separate hot water cylinder, where the water is stored until it’s needed. Unlike regular boilers (see below), there’s no cold water tank in the attic. As a result, system boilers rely on the mains water pressure to push water around the system.
Efficiency
Like other types of gas condensing boiler, system boilers are extremely efficient – around 90% efficient in fact.
Cost
Expect to pay anywhere between £1,500 and £3,000 depending on the boiler type, warranty length, required controls (plus any additional components), and the amount of work required.
Pros
There's no need for a tank in your loft
You can get hot water from multiple taps at the same time, making it suitable for larger households
Like combi systems, more components are integrated into the boiler unit itself, placing them under the protection of the boiler warranty
Cons
Requires good mains water pressure to function, so may not be suitable for older properties
Water must be heated up and stored before it can be used
The hot water can run out and you'll have to wait for it to reheat
You need to find room for the cylinder somewhere
System boilers are suitable for homes which need to have hot water in more than one place at the same time.
Conventional boilers
What is a conventional (regular) boiler?
Conventional boilers - also known as open vent or regular boilers - have both a cylinder and a tank.
How does it work?
These work in a similar vein to system boilers, storing hot water in a cylinder, which can be used in multiple outlets at the same time. In addition, a cold water tank in the loft provides a gravity-fed system for the hot water, which makes regular boilers a better choice for houses with lower mains water pressure.
Efficiency
Similar efficiency to system boilers – some energy is wasted by the stored hot water when not being used, but condensing boilers still enjoy efficiency rates of 90% and over.
Cost
Similar to system boilers – expect to pay around £1,500 to £3,000 including fitting. If major work is required – for example, to lay new pipes or find space for a cold water tank – then you could have to pay more.
Pros
You can get hot water from multiple taps at the same time
Suitable for properties with low water flow rates
Lower pressure means systems work well with older pipes and radiators
Can be the cheapest type of boiler to fit if performing a like-for-like swap
Cons
The hot water can run out and you'll have to wait for it to reheat
You need to find room for the cylinder and the tank
More external components – such as the water pump – that aren’t covered by the boiler’s own warranty
Potential for cold water storage tank to freeze in poorly insulated lofts
Conventional boilers are suitable for homes with low mains water pressure that need to deliver hot water to more than one place at the same time.
Electric boilers
What is an electric boiler?
Electric boilers are designed to slot in seamlessly in place of gas boilers to provide heating and hot water. You can purchase system, combi and heat-only electric boilers.
How does it work?
The boiler works in a similar way to condensing gas boilers – the water is heated as it’s passed through the boiler’s heating element (similar to a kettle) and then distributed directly to the heating system while hot water is sent either on-demand to taps and showers (combi) or stored in a cylinder for future use (system and regular).
Efficiency
Although technically more efficient than gas boilers (electric boilers claim 100% efficiency, so fewer kWh of energy are used), the per-unit cost of electricity is higher than gas, making them more expensive to run than gas boilers.
Cost
Electric boilers cost a similar sum to their gas counterparts – non-fitted prices start as low as £400 for a heat-only boiler, rising to £2,000 for an electric combi model. The cost of fitting is broadly comparable to gas boilers, but additional requirements (changing boiler location, potential electrical upgrades) may increase costs.
Pros
If your home is powered by renewable energy, then there are zero emissions
More efficient than gas – fewer units of energy are required to produce the equivalent amount of heat
More flexible placement – don’t require a flue or gas pipe, so can be placed anywhere in the home
No risk of carbon monoxide poisoning – no gas involved
Quieter and have fewer moving parts, so potentially more reliable
Cons
Expensive to run on a per-kWh basis compared to gas
Less efficient than heat pumps
Warranties tend to be shorter – only 2-3 years compared to 5 or more for gas boilers
Lower maximum outputs make them less suitable for larger homes
Electric boilers could be a good choice in smaller homes desperate to reduce their carbon emissions while wanting a solution that can potentially replace a gas boiler with minimal effort.
Heat-pump boilers
What is a heat pump?
Heat pumps extract latent heat from the surrounding air or ground to produce the hot water used to heat your home. Because heat pumps produce lower temperatures than gas or electric boilers, they need to run longer to heat your home to a reasonable temperature and work best in well-insulated houses.
How does it work?
Heat pumps suck in heat from the surrounding air or ground depending on their type. This heat is absorbed into a low-temperature liquid refrigerant, which is subsequently compressed to increase its temperature. The liquid then releases this heat to heat the water moving through your central heating with the remainder stored in your hot water cylinder for providing hot water when required.
Efficiency
Technically extremely efficient – the compression system actually produces more units of heat than the energy it consumes, allowing efficiencies of 200% or higher to be produced to reduce running costs, particularly in relation to more expensive forms of energy such as oil-powered and electric boilers.
Cost
Extremely expensive to install compared to gas and electric boilers at anywhere between £10,000 and £18,000. Ground source heat pumps, which deliver hotter temperatures, cost more than air source heat pumps. Since April 2022, grants of up to £5,000 towards the installation costs have been made available to homeowners.
Pros
Extremely efficient – can produce three units of heat for each unit of electricity it consumes, so an average home’s heating requirements (12,000kWh per year) can be met by as little as 4,000kWh of electricity
Produces fewer carbon emissions than conventional heating systems – and none at all if your home is powered by renewable electricity
Cons
Incredibly expensive to fit – even when you include the available grant
Air source heat pumps require enough space outside to house the external condenser, which can also be noisy and blow colder air into the immediate vicinity
Ground source heat pumps are even more disruptive (and expensive), requiring groundworks to lay the pipes in your garden
Produces less heat than gas or electric boilers, so not suitable for larger or poorly insulated homes.
Not as cheap to run as efficient gas boilers
May require local authority consent
Heat pumps are an eco-friendly way to heat your home, but may struggle to heat your property or hot water to temperatures you’ve become accustomed to.
Energy-efficient boilers
All new boilers are considered energy-efficient, and — for now — must be sold with an energy label (similar to labels on kitchen appliances).
This is a requirement of the Ecodesign for Energy-Related Products regulations.
How else can I save money on heating?
Getting an energy-efficient boiler is a great start to saving on your heating costs, but what's the purpose of heating your home if the heat escapes?
Proper insulation and draught-proofing are vital accompaniments to any energy-efficiency upgrades you make on your heating system – particularly if you install a heat pump – and installing them need not be costly or time-consuming.
Draught-proofing
If you're put off by the invasive nature of installing insulation then draught-proofing is for you. Draught-proofing starts with locating draughts around your home. Look for cracks around windows and doors or gaps between the doors and the frame.
Plugging these gaps is as easy as visiting the DIY store. Self-adhesive foam strips are great for the borders around windows, while brushes can be attached to the bottom of doors or letterboxes to stop hot air escaping.
For larger cracks around window frames, try using sealant or putty to fill them up.
For bigger gaps like a chimney flue, you will need specialist products. A chimney balloon simply inflates and blocks the chimney flue, preventing cold air from rushing in and hot air rushing out.
Insulation
Insulation is more expensive and complex to install, but is also an even bigger money-saver than draught-proofing, making it well worth the effort.
An estimated 25% of the heat lost in a typical home is through the roof. Loft insulation is the most basic form and if you have a roof and attic in your home, it's where you should start.
While new-build properties and those built in the last few years are likely to have insulation fitted, older properties may not. Even those built in the 70s and 80s with insulation may find the amount installed is now considered insufficient.
You can buy loft insulation in DIY stores and install it yourself, but you can also have it installed by a professional.
Wall insulation is an even bigger money-saver but has to be installed by a professional, and the type of wall insulation will depend on what type of home you live in.
If your home was built after 1930 then it’s probably got cavity walls, meaning an inner and an outer wall. Cavity wall insulation fills the gap between the walls by drilling holes in the outer wall and pumping in insulation.
If your home was built earlier, then you most likely have solid walls. Solid wall insulation consists of packing insulation on the inside or outside of the walls and can be expensive to install (as well as reducing the size of your rooms if fitted internally), but it can also save a lot of money.
Don’t forget to upgrade your windows too – modern double-glazing is more energy efficient than models fitted 20 or even 10 years ago.
FAQs
How much does a boiler cost?
The cost varies according to the type and size of boiler being fitted. The price of a new boiler – without fitting - ranges from under £500 to over £2,500 for the boiler.
How much is a new boiler (including fitting)?
The cost depends on how much labour (and additional parts) are required. A like-for-like swap can cost as little as £1,500 in total, while some jobs can cost over £5,000. Read our detailed guide to the cost of a new boiler here.
What is a condensing boiler?
A condensing boiler is a gas boiler produced in the last 15 years or so. All modern gas boilers – combi, system or regular/heat-only – are condensing boilers. They’re more efficient than older gas boilers because more of the energy used is converted into heat through recycling some of the energy lost during the heating process.
Which boiler type is the most widely used?
The condensing combi boiler (powered by gas) is the most popular boiler type currently being fitted in the UK.
Which type of boiler has highest efficiency?
Heat source pumps actually produce more energy per unit than they consume – each unit of energy produces two to three units of heat, making them 200-300% efficient. Electrical boilers are 100% efficient, while condensing gas boilers are at least 90% efficient. Remember, the most efficient doesn’t necessarily translate to the cheapest to run – the unit price of electricity compared to gas ultimately determines which type is cheapest (currently gas).
How long does a boiler last?
The average life expectancy of a boiler is between 10 and 15 years. You can increase the life of your own boiler by performing regular maintenance such as annual servicing by a qualified professional.
How many radiators can a boiler run?
That depends on the power rating (in kW) of the boiler. As a rule of thumb, one radiator requires 1.5kW of energy, but not all boiler types are equal.
If you’re looking at a combi boiler, which supplies hot water when it’s needed, look at 24-27kW models to heat homes of up to 10 radiators, with 28-34kW suitable for up to 15 radiators, and 35-40kW models recommended for homes with up to 20 radiators.
System and heat-only boilers, which only need to heat hot water 2-3 times a day, can be smaller – so 12-15kW are suited for homes with up to 10 radiators, 18-24kW for 10-15 radiators, and 30-35kW for homes with 15-20 radiators.
How do I know what boiler I need?
Read up on the different types of boiler above and work out which one suits your budget, household size and needs. Then use our new boiler comparison tool to find potential solutions.
