Boiler Types

In the UK, the boiler market is dominated by one particular type of boiler: the condensing boiler. All new boilers today must be condensing.

What is a condensing boiler?

A condensing boiler is a water heater that is fueled by gas or by oil. These systems achieve a very high efficiency, typically greater than 90% on the higher heating value, by re-purposing wasted heat in flue gases to pre-heat the cold water entering the boiler.

In short – a condensing boiler will reclaim heat from the waste gases and reuse it.

The government introduced legislation in 2007 that required new boilers to be more energy efficient, which has resulted in all new boilers produced being categorized as “condensing”.

A condensing boiler will help to save money on your energy bills by providing an energy efficient way of getting hot water, as you get more heat from your fuel. As mentioned previously, a condensing boiler will usually use 90% of their fuel to create heat, which earns them an energy efficiency rating of A.

So for every £1 you spend on fuel you lose 10p. Compared to old boilers, which are about 65% efficient, where you’d lose about 35p.

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There are three main types of condensing boilers that are suitable for UK homes:

1. Combination Boiler

Should I get a combination boiler?

The combination boiler, commonly referred to as a “combi” boiler, is the UK’s most popular type of boiler.

The beauty of a combination boiler is that it provides instant hot water and heating, while saving space within a home. Most combination boilers run on mains pressure water and therefore do not require tanks to be placed in the loft.

Benefits of a combi boiler:

  • Unlimited hot water, because it heats the water straight from the mains.
  • Saves space because you don’t need a cold water tank or hot water cylinder. Even better for those living in a smaller house or a flat.
  • Quicker to install because they’ve got less boiler parts than other heating systems.
  • Less pipework makes the installation typically cheaper and quicker.
  • You can have a power shower without needing a pump.


  • Good mains power is required pressure so that if more than one is being used at the same time, there won’t be a reduction in the flow of hot water.
  • Water might take a few seconds to heat up.

It is worth noting that combi boilers come in all sorts of shapes and sizes.

2. Regular Boiler

Should I get a regular boiler?

Regular boilers are also known as conventional boilers or heat only boilers. A typical regular boiler system incorporates a boiler, extended controls, a hot water cylinder which is often fed by a cold water storage cistern located in the loft and a feed and expansion cistern, which is also located in the loft.

Benefits of a regular boiler:

  • Water is sent to lots of taps at the same time, without weakening the flow of water.
  • Often an electrical immersion heater is fitted to the hot water cylinder as back-up, in case your boiler breaks down.
  • Perfect for a large home, with more than one bathroom.
  • A good option in areas where water pressure is low.
  • Compatible with solar water heating systems.


  • They don’t suit small apartments, as space is needed to install a hot water cylinder and a cold water tank.
  • You need to use the controls or immersion to heat the water in the cylinder – so you need to decide ahead of time when you want hot water.
  • The hot water can run out and you have to wait for it to reheat it again.

3. System Boiler

A system boiler heats your central heating system directly and produces hot water for your cylinder. This type of boiler has a water cylinder but no water tank, so it can be installed in homes with limited or no attic space.

Just like a regular (conventional) boiler works on the principle of stored hot water. However, a system boiler differs from a regular boiler in some important respects.

Why get a system boiler?

  • Installation is quicker, neater, easier and more efficient than a regular boiler.
  • The hot water is pumped from the system boiler through the heating system to the radiators and hot water cylinder. This means faster response and more economical running costs. The system boiler removes the need for a feed and expansion cistern.
  • There is no need for a tank in the loft, so it can be an option in a home with little or no loft space.
  • Compatible with solar water heating systems.


  • They can be costlier to buy, install and repair.
  • The hot water can run out and you have to wait for it to reheat it again.

Energy-efficient boilers

Energy efficient boilers are not a specific type of boiler – but do people often ask whether their boiler is energy efficient or not.

All new boilers are energy-efficient. Since 2010, all new boilers must be A-rated for energy efficiency or at least 90% efficient. Regardless of whether they are a combi boiler, a regular boiler or a system boiler.

The energy efficiency rating system for boilers is called SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK). The SEDBUK is a Government database that provides a simple way of comparing the energy efficiency of all boilers.

The SEDBUK rating shows the efficiency of boilers as a percentage. For a boiler to be rated as efficient, they would have to be around 90% or higher.

This rating will help in selecting a boiler that is energy-efficient or to determine how efficient your existing boiler is.

If you have an old G-rated boiler you could be losing money every year on wasted fuel. For example, an old G-rated boiler with a 65% efficiency means you are losing 35p for every £1 you spend on fuel.

To check the efficiency rating of your boiler, click here.

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