Category - Boilers
Guide author photo

Will Scholfield, Engineer

31 Jan : Updated 22 Apr ● 8 min read

Which type of boiler is right for your home?

Choosing the correct boiler and central heating system for your home can be a headache. Although your boiler is integral to your hot water and heating supply, it's unlikely you will think about it until something goes wrong, and you either need to book a repair or start the search for a new boiler.

We all know a good boiler is reliable, efficient and reasonably priced. But how will you know which one to choose if you don't know your combi boilers from your system boilers? And which is going to be most appropriate for your home?

We put together this guide to help you answer those questions and more. Here, we explore the different types of boilers, how they work, how efficient they are, and more. So you can make an informed decision when it comes to upgrading your current boiler.

What is a combi boiler?

Short for combination boiler, a combi boiler delivers heating and hot water to your home from a single unit. This means you won't need a separate hot water cylinder or cold water storage tank to be installed in your home. Combi boilers are installed in the majority of British homes due to their versatility and being fitted with an integral secondary heat exchanger that can supply hot water on demand.


How big are combi boilers?

One of the main benefits of a combi boiler is its size. A combination boiler's compact size and simplicity make it ideal for most homes. This means the boiler can usually be fitted almost anywhere in your home, including airing and kitchen cupboards.

How energy efficient are combi boilers?

Rated 'A' for efficiency, combi boilers only heat water when you need it. This differs from standard or system boilers, which heat and store hot water in separate tanks. Electric combi boilers are much more efficient because they waste less energy. A more efficient boiler means less energy is wasted, meaning you'll save money monthly when the heating bills come in.

How expensive are combi boilers?

A new combi boiler costs between £1,500 and £2,500. Generally, a combi boiler will be cheaper to install, maintain, repair, and carry out a boiler service on than most standard or system boilers. However, if you convert your system from a standard or system boiler, the initial conversion cost could be higher. 

This is because combi boilers only have one unit generating heat, so there are no additional cylinders or storage tanks to worry about. Upgrading to an A-rated combi boiler from another boiler system can also save you money in the long run, as they're more efficient and cheaper to maintain.

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What is a standard (conventional) boiler?

Sometimes known as a conventional, regular or heat-only boiler, standard boiler systems use cold water tanks to store water that fills the boiler. A separate hot water tank also stores and supplies water to your taps and radiators.

Typically, the cold water tank is located in the roof space or loft, with the hot water storage cylinder positioned below in an airing cupboard.

One downside is that you can only use as much hot water as can be stored in the storage tank, so you could run out if you’re using a lot of hot water at any time.

Standard boiler-100.webp

How big is a standard boiler?

Standard boilers are generally found in larger or older homes due to the space required to keep the separate tanks.

Due to how they work, modern standard boilers are of a similar size to combi and system boilers, but the cold and hot water cylinders take up more room.

With this being said, standard boilers can meet higher demands for water as they store large amounts of hot water in the cylinder - this means multiple bathrooms and hot water taps can be serviced at any one time.

How energy efficient are standard boilers?

Standard boilers, particularly older models, are less efficient than combi boilers. However, their usefulness in larger homes means standard boilers are still produced, and some models are over 90% efficient.

How much does a standard boiler cost?

A regular boiler will typically cost around £500 for the unit alone. However, due to the additional tanks, cylinders and controls, standard boilers are more expensive to install and maintain, especially compared to combi boilers, where everything is contained in one unit.

What is a system boiler? 

Like standard boilers, system boilers are usually found in larger homes with greater hot water and heating demands. Unlike standard boilers, however, system boilers are filled directly from the cold water mains and are connected to a sealed system. This means there's no need for feed or expansion tanks in the loft.

System boilers are usually connected to unvented hot water cylinders and provide better hot water performance when simultaneously supplying multiple taps and showers.

System boiler-100.webp

How big is a system boiler?

The actual boiler unit is similar to standard and combi boilers, although you will still need room for a hot water storage cylinder. However, there is no need for the additional feed and expansion water tanks in the loft as they are fed from the cold water main and fitted to a sealed system.

How energy efficient are system boilers?

New system boilers are just as efficient as combis in the 90% range; however, you wouldn't be heating the water instantaneously, so you would be heating a store of hot water, which could cost slightly more money. 

New system boilers are as efficient as combi boilers, with most being rated above 90% efficient. You cannot heat water on demand despite the high energy efficiency levels. Instead, you'll need to use a hot water cylinder, which will cost slightly more to keep warm.

How much does a system boiler cost?

A system boiler can cost anywhere between £600 and £2,500 depending on the make, model and type of appliance. These boilers are more expensive to have installed than combi boilers, sometimes costing up to £2,000. Having said this, system boilers are much more powerful and potentially more cost-effective than standard boilers, as there are no feed and expansion tanks to be fitted.

What is a biomass boiler?

Biomass boilers work in a similar way to other boilers, but they don't burn fossil fuels. Instead, they are a renewable energy source that burns wood pellets, plants and other natural waste to generate heat.

How big is a biomass boiler?

A biomass boiler includes fuel storage, a tank, an expansion vessel and a chimney and can occupy around 10 square metres of space. Typically kept in garages or outdoor sheds due to their size, biomass boilers are also usually kept separate from the home.

How energy efficient are biomass boilers?

The efficiency of a biomass boiler will depend on the fuel source you use. For example, it may be as high as 94% if you're using wood pellets but as low as 80% if you use wet chips.

Biomass boilers also require more upkeep than combustion boilers, as they must be kept clean and supplied with fuel.

How much does a biomass boiler cost?

Again, the specifics of biomass boilers will vary based on the type of boiler system you purchase. Biomass appliances that need to be fed manually can cost between £4,000 and £10,000, while automatic pellet-feeding systems can cost as much as £20,000.
Installation typically takes 1-2 days and could cost upwards of £400, but this will change according to who you hire.

Under the Government's Boiler Upgrade Scheme, you may be eligible for a grant of up to £5,000 to help pay for a new biomass boiler.

What is a back boiler? 

Back boiler systems are fitted behind electric or gas fires and provide central heating and hot water. Popular in the 1960s, 70s, and 80s, it has been illegal to install new back boilers that are non-condensing in UK properties since 2005, when regulations stated that only highly efficient condensing boilers could be installed in homes.

If your home still uses a back boiler, we strongly recommend exploring upgrades to a newer, more energy-efficient, environmentally-friendly boiler.

How big is a back boiler?

The boiler system is a large unit located within the chimney breast, behind the fireplace. In addition to the boiler unit, back boilers need a feed and expansion tank in the loft and a hot water cylinder to be fitted into the property.

How energy efficient are back boilers?

Compared to other boilers, back boilers are not efficient. In fact, the installation of non-condensing back boilers was banned in 2005 due to the high carbon emissions and Government safety regulations. Back boilers are only around 80% efficient, so for every pound you spend on heating your home, you lose 20p up your chimney.

How much is maintenance on a back boiler?

As well as being expensive to run, back boilers are costly to maintain and service. Servicing costs would be higher due to the level of work required on them, while certain parts may be hard to come by or even obsolete.

Rather than maintaining your current back boiler, it is recommended that back boilers are replaced with economical condensing boilers.

Which boiler model is suitable for my home? 

A new boiler might not be your most exciting purchase this year, but it could be the most important one. So you must make the right choice.

We understand you'll want to do your due diligence before your new boiler is installed. To help you, we've compiled a series of guides relating to the installation process.

From the signs you need to replace your boiler to everything you need to know about moving a boiler and how much it costs to install a central heating system, the BOXT guides have it all.