Types of Boilers Explained

Deciding on the best boiler for your home can be a confusing process. You must consider efficiency, property size, and lifestyle when choosing a suitable boiler system. If you are looking to buy a new boiler it is therefore imperative that you know which type of boiler will work best in your home.

The guide below outlines the types of boilers available so you can establish which one you need to suit the requirements of your property. We discuss the systems, how they work, their advantages and what kind of homes they work best in.

What are the different types of boilers?

When researching types of boilers, you may come across the terms condensing and non-condensing boilers. These terms describe the type of technology within the boiler, i.e. how the boiler uses fuel to produce heat for your home. However, you will not need to choose between these types as, by law, all modern boilers now use condensing technology as standard.

In terms of the physical type of boiler, there are three main types: combination (combi) boilers, heat only boilers and system boilers. As a quick summary, heat only boilers (aka conventional or regular boilers) work with a cylinder in the airing cupboard. System boilers are often found in modern homes with an unvented hot water cylinder. Finally, a combi boiler produces instant hot water.

The below sections will take each of these three boiler types in turn and help you to identify which one is in your home and the advantages and disadvantages of each. If you're thinking of purchasing a new boiler, our guide will help you decide whether to stick with your existing boiler type or install a different boiler type.

Combi boilers

A combination boiler (or combi boiler for short) provides both heating and hot water directly from the mains in one single compact unit. They do not need a separate hot water tank like regular or system boilers. A combi boiler can use a variety of different fuels depending on the make and model.

Read our expert guide to learn more about what is a combi boiler

To learn more about the advantages and disadvantages of each fuel type, read on to the next section to discover which is the best fuel type for your home.

Conventional Boilers

A conventional boiler (also known as a regular boiler, a conventional boiler or a traditional boiler) offers a more traditional heating alternative for the home as it only provides heating. Also known as conventional boilers or heat only systems, a regular boiler is commonly found in older properties. These systems require a large amount of space for installation due to the need for a cold water cylinder and cold water cisterns. Much like combi boilers, regular boilers come in a variety of different fuel types.

System Boilers

A system boiler functions in a similar way to a regular boiler system as it provides the heat for your central heating system and produces hot water that is stored in a hot water cylinder until it is needed. System boilers can use 3 different types of fuel: gas, oil, and LPG.

Boiler fuel types

Most homes in the UK are connected to the gas grid so are most likely to have a natural gas boiler in their home. Properties in rural areas that aren't connected to the gas grid will use an alternative fuel source such as oil, electricity or biomass (wood pellets).

More and more homeowners (even those who have access to gas) are choosing to install a boiler or heating system which uses renewable fuel such as a biomass boiler or a heat pump to lower their carbon emissions.

Below we outline the different types of fuel available in the UK and the advantages and disadvantages of each.

Gas Boilers

Gas boilers are the most common type of boiler in UK homes as the majority are connected to the gas grid and so opt for a gas boiler.

Advantages of gas boilers

• Cheaper to run than electric boilers: It’s suggested that gas is around three to four times cheaper than electricity per kWh. This makes it a much more economical option when heating your home despite a gas boiler not being 100% energy efficient, in comparison to an electric boiler, you will get more heat for your money with gas.
• Cleanest fossil fuel: Despite fossil fuels not being good for the environment, gas creates less than half of the CO2 emissions of oil and a third of those produced by coal. This makes it the cleanest fossil fuel of those available.

Disadvantages of gas boilers

• Expensive to be connected to the gas grid: You must be connected to the gas network to power a boiler with gas but this can be expensive to do if you aren’t already connected.

Electric Boilers

Electric boilers work by heating cold water that runs through them with a heating element. Due to this method of heating water, they are considered one of the least wasteful boiler options as there is minimal heat loss.

Advantages of electric boilers

• Perfect for small households: An electric central heating boiler is a great option if you don’t have much space and are looking for a compact boiler. They have fairly simple technology and are usually cheaper to install than other boiler types.
• Reliable alternative to gas: They are a great alternative to a gas boiler as they don’t need to be connected to the gas mains, reducing the needs for Gas Safe Registered Engineers, and so means there isn’t a risk present from carbon monoxide.
• Highly energy efficient: An electric boiler is around 99% efficient.

Disadvantages of electric boilers

• High cost and reliance on electricity: If your property is prone to power cuts or outages regularly, this boiler type may not be suitable for your household as it runs purely on mains electricity. Also, since it only runs on electricity, energy bills and running costs for electric heaters will cost a lot more in comparison to energy bills from a gas boiler.

Oil Boilers

Oil boilers are usually found in properties that can't be connected to the gas mains and act as an excellent alternative to electric boilers if you don't want to pay for the expense.

Advantages of oil boilers

• No need for a gas supply: If your property is not connected to the gas mains and has no way of doing so, oil boilers are one of the most cost-effective alternatives.

Disadvantages of oil boilers

• Oil is expensive: Oil is one of the most expensive fossil fuels and it’s running out meaning it's not always available and on-demand for you when you need it most. Some oil suppliers will insist on you paying for your oil on delivery, which you have to remember to bulk purchase in advance, rather than in monthly instalments making oil a large financial cost.
• Storage space required for an oil tank: When you do get your oil delivered, you will then need to store it in an oil tank on your property somewhere until you need to use it. This can take up a great deal of space, especially if you have it above ground, which needs to be placed on level, non-combustible soil.

Liquefied petroleum gas Boilers

Liquefied petroleum gas (LPG) boilers use an external fuel tank that is connected to feed the boiler. With LPG being denser than regular gas, a substantial quantity can be stored in a relatively small space, making them the ideal solution for homes that do not have access to a mains feed gas supply.

Advantages of LPG boilers

• More compact and a range of options: Most LPG boilers are smaller in size than their oil or gas counterparts, often having a lower noise output. This means big name brands such as Worcester and Vaillant can have a wider range of models.
• A cheaper and cleaner boiler option: One of the cheapest boilers of the different types of boiler we’ve discussed, LPG boilers are not only good for your wallet but the environment too. Despite it still being a fossil fuel, it produces around 15%-20% less carbon.

Disadvantages of LPG boilers

• Expensive fuel cost: The unit price per kWh of LPG is higher than both natural gas and oil.
• Bulk ordering and storage: Like oil, LPG also needs to be ordered in bulk in advance of you running out and stored in a storage tank on your property which can take up a lot of space.

How to tell which type of boiler you have?

To help you identify which type of boiler you have in your home, we've detailed the three most popular types of boiler below to help you in your understanding.

Combi boiler features

• Instantaneous heating to radiators and hot water supply: with copper pipes coming out of the bottom of the boiler, combi boilers are the fastest and most convenient type of boiler out there.
• Compact to not take up space: Combi boilers don’t need an external pump or hot water cylinder taking up extra room in your loft space, meaning they use a lot less pipework on the installation too.
• Perfect for flats or small houses with only one bathroom.
• Disadvantages: Combination boilers are not suitable for homes that exceed one bathroom or have multi-jet showers as the higher demand will negatively affect performance.

Regular boiler features

• Hot water cylinder and cold water tanks: The biggest identifiable feature of a regular, conventional boiler is the hot water cylinders and a cold water storage tank that will be found in the roof space. You’ll probably also have an external pump to help the water move throughout your radiators and heating systems.
• They are also the perfect choice for homes where water pressure is low and can reduce your carbon footprint when connected to a solar water heating system.
• Perfect for large houses that require hot water from multiple outlets at once.
• Disadvantages: You’ll have to make space for a hot water storage tank in the loft or airing cupboard, which if the water runs out, you’ll have to wait for the water to refill and reheat.

System boiler features

• Internal components hidden within the boiler itself: System boilers have many of the components required to provide efficient heating and hot water into the boiler itself. Unlike a regular boiler, a feed and expansion cistern is not required as the hot water is pumped directly from the system boiler.
• Perfect for bigger homes or large properties that require hot water from multiple outlets (including multiple bathrooms) at once.
• Disadvantages: Unlike a combi boiler, system boilers don’t provide instant hot water and the amount it can provide is limited to the size of the hot water storage cylinder.

What type of boiler do I need?

Depending on your living situation, certain types of boiler will be better suited for different types of homes. Below will give you an idea of the sorts of boilers you can purchase based on the three most common types of the boiler above, but if you need a more accurate calculation, we have a boiler buying guide available that will help you find the right replacement boiler or a new boiler to suit your home and central heating system requirements.

For a quick overview of boiler sizes, please see the table below:

Property Type	No. of Bedrooms	No. of Bathrooms	No. of Radiators	Recommended Boiler Size
Apartment/Flat or House with up to 2 bedrooms	1-2	1	Up to 10	24kw-27kw
Apartment/Flat or House with 2-3 bedrooms and 1 shower	2-3	1	Up to 15	28kw-34kw
House with 4+ bedrooms and 2 showers	4+	2+	Up to 28	35kw-42kw

We have created an informative guide that will help you to decide which size boiler you need for your home if you're thinking of replacing or changing boiler types.