6 Different Types of Boilers Explained
At Intergas Heating, we help homeowners make informed choices for efficient, reliable home heating. We also provide training for installers. In both, explaining the types of boilers available for home heating is vital. Once you know the boiler options on the market and the differences between them, you can choose the most effective for your property or for your installation customers.
What Are the Different Types of Boilers for Homeowners?
There are three main types of home boilers and three lesser-known options to be aware of.
The main types of boilers are combi boilers, system boilers and regular or heat-only boilers, and there are also storage combi boilers, condensing boilers and biomass boilers.
You might choose a different boiler type depending on your central heating system, your lifestyle or your budget. Some are more efficient than others and choosing the wrong type could lead to slower water heating or higher bills.
What Is a Combi Boiler?
“Combi” is short for “combination”, and a combi boiler provides both central heating and domestic hot water for washing and cleaning.
A combi boiler is plumbed directly into the mains water and gas supplies. They use a gas flame to heat water on demand, which is then distributed to radiators and taps.
What Is a Heat-Only Boiler?
Heat-only boilers are also called ‘conventional’ or ‘regular’ boilers, because they are the traditional central heating boiler installed in homes since the 1950s. They provide heat directly to radiators and store hot water in an insulated tank for later use.
These conventional boilers are fed by both mains cold water and a cold-water feed tank, filled from the mains and used to top up the boiler.
What Is a System-Only Boiler?
A system boiler works similarly to a heat-only boiler, with a hot water storage tank rather than on-demand water heating.
The difference is that system boilers are a closed system, with no cold-water feed tanks in the loft. System-only boilers are a simplified version of the regular or heat-only boiler.
What Is a Condensing Boiler?
Condensing boilers are more modern versions of combi, heat-only and system boilers. They capture the heat from gases that are released as waste products from fuel combustion. The heat is used to heat water returning from your central heating system.
This means that condensing boilers are more efficient than older boilers, producing more heat units per fuel unit. This means your bills will be lower and you’ll have fewer carbon emissions for the same amount of heat.
Any boiler installed since 2007, whether combi, system or heat-only, will be a high-efficiency condensing boiler if building regulations are adhered to.
What Is a Biomass Boiler?
A biomass boiler burns wood chips, logs or waste timber instead of gas. The fuel is either manually or automatically fed into the boiler and burned to generate heat, which is sent to radiators, underfloor heating and a hot water cylinder for washing and cleaning use.
What Is a Heat Pump?
A heat pump is a low-carbon alternative to a gas boiler or biomass boiler. Rather than burning fuel, heat pumps use refrigerant fluid to absorb ambient heat from either the exterior air or the ground. This is the opposite of how an air conditioner works, with a few extra steps.
The refrigerant fluid evaporates when it reaches between 4-10°C, flowing into a compressor, which increases the temperature of the vapour by pressurising it at high rates.
The high-temperature, high-pressure vapour transfers its heat to mains water inside the building.
The refrigerant condenses, to be depressurised in an expander valve and pumped back around to the evaporator coil outside.
The newly heated water is distributed to radiators, underfloor heating or a highly insulated hot water tank.
Heat pumps typically work at 300% efficiency, generating 3 heat units for every 1 unit of electricity used to drive the pump, without any direct CO2 emissions.
Hybrid Heat Pump and Boiler Systems
While heat pumps are excellent low-carbon heating systems, they use a lot of electricity when external temperatures drop below five degrees. Hybrid systems give homeowners the option of switching to gas heating when it is more affordable.
Pros and Cons of the Different Boiler Types
Pros of a Combi Boiler
Up to 94% efficiency
Take up less space
Neat appearance
Easy maintenance
Instant hot water
Cons of a Combi Boiler
Only one hot water source at once
Limited by mains water pressure
More moving parts than heat-only boilers
Because a combi boiler does not need a hot water tank, they are compact and provide hot water on demand. However, the rate of heating is reduced when water is demanded in more than one place, such as the shower and the kitchen sink. If you only have one bathroom, and there are fewer than five adults in the house, you can usually avoid the cold shower this sometimes causes.
In some cases, mains water pressure is too low for a combi boiler to work efficiently.
Pros of a Heat-Only Boiler
Great for larger households
Back-up water heating
Works well with older heating systems
Cons of a Heat-Only Boiler
Many parts take up a lot of space
Complex installation – higher costs
Heat loss from hot water storage
Delays in heating hot water
A heat-only boiler is good for larger households with multiple bathrooms, as the hot water can be distributed to many points around the house at once. They are excellent for older radiator systems, which can leak when faced with the high water pressure a combi boiler or system boiler delivers.
However, this older system is less popular and less efficient. It’s possible to run out of hot water, having to wait for the tank to refill. Because the hot water is stored in a tank, heat is lost as the water cools, making heat-only boilers less efficient than other systems.
They also take up a lot of storage space, with cold water feed tanks and hot water cylinders. This complexity makes heat-only boilers expensive to repair and install, so unless you are replacing an existing heat-only boiler, it isn’t worth considering one of these. Most heat-only boiler systems are now replaced with system boilers.
Pros of a System-only Boiler
Great for larger households
Back-up water heating
Integrated system, less complex
Cons of a System-only Boiler
Hot water tank takes up space
Delays in heating hot water
Heat loss from hot water storage
Limited by mains water pressure
A system-only boiler is a halfway house between combi and heat-only boilers. They have a hot water tank that can provide enough hot water for multiple bathrooms. Installation is less complicated than heat-only boilers, as the pumps and valves associated with conventional boilers are integrated into the boiler itself. This means these parts are also covered by the manufacturer’s warranty.
However, system boilers also face the same associated problems as conventional boilers, with heat loss and delays in hot water delivery.
They take up slightly less space than conventional boilers, and more than combi boilers. Like combi boilers, they often struggle in areas where the mains water pressure is low.
Which Type of Boiler Is Right for My Home?
To decide which type of boiler is best, homeowners should consider the following points. Alternatively, use our helpful boiler finder tool to get a recommendation.
Hot Water Demand
For homes with a single bathroom and fewer than 10 radiators, a combi boiler is perfect. It will manage hot water and heating on demand in an efficient way without struggling to meet your needs for hot water.
With multiple bathrooms or more than 10 radiators, a system boiler is ideal. It will heat enough water to cover everywhere it is needed. Installation is more straightforward than conventional boilers.
Existing Infrastructure
If you currently have a combi boiler that is struggling to serve multiple hot water outlets at once, or your water pressure is causing issues, switching to a system boiler can solve these issues, but it will require space for the hot water tank.
Space Considerations
If you’re short of space for additional tanks, a combi boiler is the right option. If you still need a high hot water supply for multiple bathrooms, consider a hyper-efficient combi boiler.
Intergas Offers Industrial Boiler Training
At Intergas, we support newly-qualified installers and heating engineers with free training on all our boiler and heat pump products. Our free boiler training courses are trusted by 1,500 engineers every year, combining hands-on experience and flexibility to grow your toolkit. Courses are delivered in Kidderminster, Liverpool and Paignton.
We also provide training for hybrid heat pump installations, delivered by home heating experts to help engineers gain future-ready skills and confidence in low-carbon solutions, without the usual expense.
Free Training Courses
- Boiler installation course: how to install, service and troubleshoot Intergas combi boilers. A free, one-day practical training course.
- Air Source Heat Pump training: learn to design Air Source Heat Pump systems, survey sites and install our Xceed heat pumps.
- Hybrid ASHP course: how to install and commission Intergas Xtend hybrid heating systems.
- Renewable Heating Training: With our cross-over course, you can train to install Intergas boilers and ASHP systems in a single day.
FAQs: Boiler Types
What are the most common types of boiler?
The most common boiler types in the UK currently are the condensing combi boiler as the most common, followed by system boilers and heat-only boilers.
What will replace boilers after 2025?
While gas boilers are highly efficient, they are a large source of CO2 and NOx emissions. By 2050, the UK government are aiming to achieve Net Zero emissions, and a large part of their plan to achieve this is to encourage homeowners to install Air Source Heat Pumps through the Boiler Upgrade Scheme.
However, replacing existing boilers is not mandatory. The “Gas Boiler Ban” instead requires all new build residential properties built after 2025 to have an alternative heating system, such as heat pumps and solar-powered heat systems.
What is the most efficient boiler type?
Of all the boilers on the market, a condensing combi boiler is the most efficient at up to 94% efficiency.
Beyond boilers, heat pumps are much more efficient, producing 3 heat units for every 1 unit of electricity used.
