Which boiler? A guide to the different types of boiler system

If you’re looking to upgrade your boiler to a newer, more energy-efficient model, you’ll need to figure out which type of boiler is best for your needs.

There are many factors to consider, from the size of your property to the number of bathrooms and radiators, and each of these will help determine which one is best for you.

In this guide we will explain the main types of boiler and their functions, as well as offer our advice on which type is best for you.

What is a condensing boiler?

Condensing boilers are the most efficient on the market, meaning you use less energy and save money in heating costs. Since 2005, all new boilers that are installed in homes in England and Wales must be condensing ones. If you’re upgrading from an old non-condensing boiler, you could save hundreds of pounds every year.

Condensing boilers are more efficient because they use a larger heat exchange and are able to recycle some of the heat they generate back into the system. In a non-condensing boiler, hot gases are exited via the flue and lost. Condensing boilers capture these gases and use them to help heat up the water, meaning the burner does less work. This increases your energy efficiency, decreases your bills, and also helps to reduce your carbon footprint.

There are several different types of condensing boiler to choose from, including combi boilers, system boilers, and conventional boilers, and each of them has their own advantages and disadvantages. We will discuss each in turn below.

What is a combi boiler?


  • Instantly responds to tap and radiator usage
  • No need to leave time between showers or wait for heating
  • Water supply comes straight from the mains
  • Doesn’t take up much space
  • No need for a tank or cylinder in the loft space
  • Less pipework so easier to maintain
  • Decreased risk of having your pipes freeze


  • Aren’t the best choice if you have low water pressure
  • Can only use hot water for one task at a time
  • May not be the best choice in a larger home with multiple bathrooms
  • Your shower may be incompatible
  • More moving parts in the unit means more can go wrong

For most modern homes, a combi boiler is typically the best choice. They control both your heating and hot water efficiently. Rather than storing hot water in a large tank, they only heat water when you need it, meaning you can have unlimited access without the need to wait for a tank to refill.

Plus, the units are relatively small, and you won’t need somewhere to store water, so you’ll be able to save space in your home. This also means less pipework is required, which requires less installation work and decreases the risk of your pipes freezing.

All boilers come with efficiency ratings, and combi boilers are usually ranked in the A category, meaning they are over 90% efficient. This allows you keep your heating bills low while also saving space. This is why they have become so popular across the UK — especially in smaller homes.

That said, they aren’t ideal for everyone. If you are upgrading to a combi boiler, your old shower may not be compatible. Because combi boilers use mains pressure, they may not work with pump-assisted power showers. This also means that if you have low mains water pressure, your tap and shower pressure will be low.

The other downside is that they can only heat up a limited amount of water at a time, meaning you won’t be able to use hot water from multiple taps at once, which typically isn’t ideal for large families with multiple bathrooms.

What is a system boiler?


  • Pump means quick and economical operation
  • Designed to be as compact and space-saving as possible
  • Allows for a constant hot water supply
  • No need for bulky feed and expansion tank
  • Can work easily with solar panels


  • Take up more space than a combi boiler
  • You may have to wait for more water to heat up
  • You need space for a cylinder
  • The size of the cylinder will dictate how much water you can use
  • Must be insulated to prevent heat loss

A system boiler is probably preferable to a combi boiler if you have a larger home or need to supply more than one bathroom. You won’t have to install a feed and expansion tank as system boilers contain a pump and expansion vessel within the unit. You will, however, need a cylinder to store water. This is ideal for larger family homes with multiple bathrooms, as it allows you to use hot water in various places at once.

Most of the main components are contained within the unit itself, so installation is fairly straightforward. Because there isn’t a need for a tank in the attic, you don’t have to worry about leaks or frost damage, and a cylinder is much easier to maintain. Another plus is that they can be integrated with solar panels, allowing you to reduce your bills as well as your carbon footprint.

The downside is that they take up a considerable amount of space compared to a combi boiler, and you will have to wait for more water to heat up if you empty the tank. The size of the cylinder is up to you, but smaller ones will mean you’ll run out of hot water sooner. Stored heat will also cool over time, wasting energy, so insulating the cylinder is key.

What is a conventional or regular boiler?


  • Allows you to use multiple taps and bathrooms at once
  • Are a great choice if you have low water pressure
  • Compatible with older heating systems
  • Install a heating element in the cylinder will allow you to still get hot water if the boiler breaks down
  • Compatible with solar panels, increasing energy-efficiency


  • Requires a lot of space
  • Pressure flow can be low
  • Hot water may not always be available and may take time to heat up
  • Can be harder and more expensive to install compared to combi and system boilers
  • Not as efficient as heat will be lost when stored

A conventional boiler — also known as a regular boiler— uses both a cylinder and a tank to store water. They’re ideal for large family homes as you’ll have plenty of hot water to go around, which can be used in multiple bathrooms. As with system boilers, they can be easily powered using solar panels, allowing you to reduce your bills as well as your carbon footprint.

Conventional boilers are generally best for homes that already have a conventional heating system, as the lower pressure makes them better for older radiators. This also means the pipe infrastructure is already in place, and the amount of work required will be minimal. Another positive is that they are compatible with solar panels, allowing you save money and be more eco-friendly.

Unfortunately, these are the largest types of boiler, and take up a lot of space in your home. This also means that they are more difficult to install than other boiler systems. Like a system boiler, it won’t heat water on demand, which can be a problem if you use up all your stored hot water.

What is a back boiler?


  • Can improve the efficiency of a stove or fire
  • Uses heat from flue that would otherwise be lost


  • Produces more harmful toxins than other boilers
  • More expensive to run compared to other boilers
  • Lacks the energy efficiency of more modern boilers

Unlike the other boilers in this list, a back boiler is not a condensing boiler, and therefore new ones cannot be installed into properties, as per the law. As the name suggests, they are boilers that are attached to the back of a fireplace or stove, allowing it to provide heat for both central heating and hot water.

They have been in decline since the introduction of condensing boilers due to their relative inefficiency and increased running costs. The other downside is that back boilers produce many more harmful toxins than newer boilers.

If you have a back boiler in your home, it is best to upgrade it to a more economical combi boiler. This could save you hundreds of pounds each year. If you want to upgrade your hot water system, you can find a new boiler with All England Gas. Complete our online survey or request a home survey, and we will offer you a range of suitable boilers to choose from.

Which boiler should I get?

When it comes to choosing a new boiler, it’s important to remember that every property will have different heating requirements. To determine which boiler will be the best choice for you, there are a few things you will need to consider.

Below, we will walk you through the main considerations to help you make the best decision. Alternatively, you can take our online new boiler survey and get a recommendation straight for us.

Is your property connected to the gas network?

The majority of homes are connected to the gas grid and use a gas heating system. But there are still hundreds of thousands of homes that rely on other systems, such as oil, particularly in rural areas.

If you aren’t connected to the grid, oil-powered central heating systems can be a great alternative, but they are much more expensive than gas boilers. You can find out more about heating premises that are off the mains gas network on the OFTEC website.

How many people live in your property?

The number of people that live in the property is a key question, as this will determine the size of boiler you need. If it’s too small, it won’t be able to heat your whole home or provide enough hot water at the busiest times. Likewise, if you choose one that’s too big, you could produce more energy than you need, increasing your bills. Large families that use a lot of water will likely prefer a conventional or system boiler, while a combi boiler is perfect for smaller homes.

How many bathrooms are in your property?

Similar to the above question, the number of bathrooms should factor into your choice of boiler. If you have more than one bathroom and multiple people using them at once, you’ll have large hot water demands. Most combi boilers are only suited to a home with one bathroom, while conventional or system boilers are generally better for larger homes with multiple bathrooms.

Is there space in the loft or an airing cupboard?

Think about the extra space you have in your loft or any cupboards and closets that could be used for a water tank or cylinder. If you need lots of heat and hot water and have plenty of space, a conventional boiler with a storage tank could be the best choice. Conversely, if you don’t have any extra space, a small combi boiler is likely the best choice. The downside is that you won’t be able to get hot water from multiple taps or showers at once.

How many radiators are in your property?

The number of radiators that you currently have in your home can determine the power that your boiler will need. The more kilowattage, the faster the flow rate will be. If you have fewer than 10 radiators, you’ll probably want a 24 to 27kw boiler. Around 15 radiators and you’ll want a 28-34kw boiler. While the largest homes will want a 35kw to 42kw boiler.

Choosing the right boiler for your home doesn’t have to be a hassle. Find a new or replacement boiler with All England Gas and keep your home warm all year round. We offer installation and affordable pay monthly plans, as well as boiler cover, so get in touch today.

Still have questions?

Call us now! 0800 193 1938