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How to know which boiler to choose.

With marketing materials including so much technical jargon, it can be difficult to know which boiler is right for your home.

Your boiler is likely going to be with you for at least a decade, so it is important to choose one that meets the needs of your home and lifestyle.

It is essential to consider factors such as your current hot water usage, how this may change in the future, the size of your property as well as your existing heating system and the types of fuel available at your property.

In this article we will layout the basics into easily understandable language, to make choosing a new boiler a little easier.

Types of boilers

First things first, it is important to consider the three major types of gas boilers available, to determine which one is most appropriate for your requirements.

Most boiler manufacturers offer three main types - combination (combi) boilers, system boilers and regular boilers, here is a basic overview of their differences and general applications:

Combination (Combi) Boilers

Combi boilers are by far the most common gas boiler installed and used in UK residential properties.

They provide both instant hot water and heating water from a single unit and take water directly from the mains.

As a result, they do not require a separate hot water storage cylinder and so are very easy to store, making them ideal for properties with a limited amount of space.


  • The smaller size makes them great for properties with limited space.
  • No need for a hot water storage cylinder.
  • No need for a cold-water cistern tank.

Regular (Conventional) Boilers

A regular or conventional boiler is comprised of two main parts – the boiler itself and a separate hot water storage tank. It can provide both hot water and heating water, in fact, they were one of the first heating system designed for central heating.

The boiler heats the water, which is then stored within the tank ready to be used. Coldwater is fed into them via a cistern installed in the attic, which naturally feeds water into the system with the help of gravity.

Regular boilers can provide a higher flow rate of water and for this reason, are more suitable for larger homes with multiple outlets e.g. multiple bathrooms.

Since they do not rely on high pressure, they are also suitable for older heating systems that may not be able to cope with the high pressure of a closed system used in a combi or system setup.

Additionally, they are ideal for areas that suffer from low-pressure mains supplies, that may not be able to cope with the pressure demands of combis and system boilers.

It also makes sense to install a regular boiler if you already have traditional heating and hot water system connected to a hot water storage cylinder. Otherwise, you would likely need to pay for the cost of conversion and potentially other new components.


  • Ideal for homes with multiple hot water outlets.
  • Ideal for areas that suffer from low water pressure.
  • Good choice for those with traditional heating systems.

System Boilers

System boilers are a modern take on the regular boiler, but with a whole host of new benefits.

Like regular boilers they have a separate boiler and a hot water storage cylinder, making them more suitable for larger properties with greater demands for hot water.

Since they have their own internal pump and expansion vessel, they do not require a cistern to be installed in the attic, making installation easier and limiting the need for additional space.

The fact that they do not need loft space also means worries about potential leaks or freezing in winter is eliminated.

As previously mentioned, the high-pressure nature of this closed system means that they may not be suitable for homes with older heating systems. Nor will they be suitable for areas with low pressure.


  • Ideal for homes with multiple hot water outlets.
  • No need for a loft tank.
  • Internal components make installation easier.

 What fuel does your home have?

The type of fuel your home is supplied with is another important factor. All the major types of boilers i.e. system, combi and regular boilers are available in gas, oil and liquified petroleum gas (LPG).

Typically, gas boilers are the cheapest type of boiler to run since the price of gas is much cheaper. Yet for those that live in rural or remote locations or areas with no gas supply, LPG or oil variants may be a suitable alternative.

What size boiler do you need?

A boiler size refers to its power output rather than its actual physical dimensions. For boilers, the unit of power is measured in kilowatts per hour (kWh), therefore the higher the kW, the greater the boilers ability to meet hot water and heating demands.

Most of the leading boiler manufacturer’s offer their boiler models in a range of sizes. Generally, engineers gage what size boiler you need based on the number of radiators in your property.

For example, if you live in a small flat with a few radiators, then a small combi boiler would be suitable and help you save money on your energy bills. On the other hand, if you live in a large property with many radiators, you are going to require a large-sized boiler to meet the heating demands.

Consider your heating and hot water demands

Do you have a large family with a lot of demand for hot water?

If you live in a property where it is likely that multiple bathrooms are going to be used simultaneously, it is unlikely that a combi boiler is going to meet your demands.

A combi boiler heats water directly from the mains water supply, so the amount of water it can provide to multiple outlets at once is limited. Therefore, if you think you need a greater supply of hot water than a combi can supply, you may want to consider a regular or system boiler instead.

Both regular and system boilers utilise a hot water storage cylinder, so can provide a larger supply of hot water and provide adequate flow rate and temperature even when there is a greater demand.

Do not buy an oversized boiler

It may be tempting to buy an oversized boiler as an easy one size fits all solution, but there is no advantage to installing a larger boiler than you need.

If your boiler is too large, you may end up using more energy than you need to, ultimately meaning you end up emitting more carbon and spending more money on your bills than you needed to.


Choosing a new boiler is a pretty simple process once you have figured out what your hot water and heating demands are.

Most UK households use gas combi boilers, with regular and systems a close second. In the unlikely the event that you do not have a natural gas supply, you can opt for an oil or LPG boiler instead.

If you need an old boiler replacing, but can’t afford to pay for it directly, you may want to consider a boiler on finance, you may even be entitled to a boiler grant, if you meet certain criteria.

Direct Heating Supplies always recommends you speak with a Gas Safe registered engineer before purchasing a boiler.