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How to choose an energy efficient boiler

With Ofgem recently announcing a 54% rise in energy bills from April for 22 million households across the UK, it’s never been more important to have an energy efficient boiler. So, if your current boiler is knocking on a bit, it might be time to consider investing in a new, more efficient model. You’ll benefit from increased comfort, cheaper energy bills and a smaller carbon footprint - so it’s win-win. But how do you choose an energy efficient boiler? In this guide we help you to understand how you can make energy savings with an efficient new boiler and explain how to select a boiler with the most efficiency potential.

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With Ofgem recently announcing a 54% rise in energy bills from April for 22 million households; it’s never been more important to have an energy efficient boiler. 

So, if your current boiler is knocking on a bit; it might be time to consider investing in a new, more efficient model. You’ll benefit from increased comfort, cheaper energy bills and a smaller carbon footprint – so it’s win-win. 

But how do you choose an energy efficient boiler?

With all the innovations in the heating market, it can be daunting to know where to start!

But spending a little bit of time researching your new heating system can pay off enormously. If you choose your new boiler correctly; you’ll end up with a reliable system that’s cheaper to run and easier to use.

In this guide we help you to understand how you can make energy savings with an efficient new boiler. And explain how to select a boiler with the most efficiency potential.

You might like our related blogs: Your options with a boiler replacement and 6 Top tips for buying a new boiler.

Why do I want an energy efficient boiler?

efficient boiler

It seems like everyone’s talking about improving energy efficiency at the moment – but do you know why?

Let’s look at why choosing an energy efficient boiler is so important:

Energy efficient boilers save you money

In simple terms, efficiency is the amount of fuel your boiler needs; to burn to do its job of heating up your home and your hot water.

Inefficient boilers are gas guzzlers. They need to burn much more fuel than an efficient boiler does, to do the same job.

And with the wholesale price of gas skyrocketing by up to 400%; we simply can’t afford to be burning more gas than we need to! 

The 54% increase in energy bills from April; will result in an annual increase of £693 to £1,791 for the average user. While homes on prepayment meters will see costs go up by £708 to £2,017.

By getting an energy efficient boiler; you’ll be able to create more heat from less fuel and minimise what you’re paying out.

Energy efficient boilers are better for the environment

In addition to saving you money, an efficient boiler will reduce your carbon footprint. If you followed COP26 last year, you’ll understand how important it is!

What do the energy efficiency percentages mean?

So, you understand why it’s important to have an efficient boiler, but what do the energy efficiency percentages mean?

We should start by saying that whilst it would be lovely if boilers were 100% efficient, they’re not. No boiler is 100% efficient. Some heat will always be ‘lost’ or used by the boiler during the heating process.

Let’s say your boiler is ’92% efficient’. The percentage refers to the total energy (fuel) used by the boiler to provide useful heating and hot water.

A boiler with 92% efficiency will use 92% of the energy to heat your home and hot water. And 8% is ‘lost’ in the process.

You might also have heard the energy efficiency of boilers being described with a letter from A-G. This is the Energy Related Products or ErP scale.

Boilers, like other appliances in your home; have to be rated on this scale to help us to identify more energy efficient products:

A – 90% and above

B – 86-90%

C – 82-86%

D – 78-82%

E – 74-78%

F – 70-74%

G – below 70%

Why are modern boilers more energy efficient?

A zombieModern boilers are much more efficient than they used to be. Because they have condensing technology as standard, and have to follow the Boiler Plus Regulations on energy efficiency.

All new boilers must be A-rated for efficiency with a minimum ErP rating of 92%.

All gas and oil boilers must now have appropriate time and temperature controls fitted. And combi boilers must also have one of four additional energy saving devices fitted.

But if you have an older; non-condensing boiler; which pre-dates the rules on energy efficiency; it will be much less efficient.

For example, if you have an old G-rated boiler with 60% efficiency; only 60% of the fuel burned by your boiler will actually go into heating your home. The other 40% will be wasted by the boiler!

In this situation, investing in a new boiler is a no-brainer. It will save you a significant sum on your energy bills.

According to The Energy Saving Trust, you could save as much as £340 a year on your gas bill; if you’re trading in an old-style non-condensing boiler for a new condensing one.

But this figure is likely to be significantly higher now, given the sky-rocketing price of gas!

How do I choose the most energy efficient boiler?

A woman with question marks above her head.If you’ve decided you want to replace your boiler for a more energy efficient one; your next question is likely to be: which boiler is the best?

This is a tricky question to answer because what’s right for you, won’t be right for everyone. It will depend on your home, lifestyle, and budget.

But you might like to read our list of our top combi boilers for 2022 here.

But whilst we can’t give you a one-size-fits-all boiler for everyone to install and immediately save energy; we can advise you on the things you need to consider to find the most energy efficient option for you: 

Choose the right installer

The first and most important step in getting your perfect heating system is finding an expert installer.

We’ve said it before, and we’ll say it again… your boiler is only going to be as good as the engineer who installs it!

Just because your boiler says 94% efficient on the box, doesn’t mean it’ll run this way for you. If it’s been set up by someone who doesn’t know what they’re doing; you won’t get the best out of it.

The Heating Hub explains that there’s a worrying skills gap amongst gas engineers.

According to them, a staggering 99% of installers haven’t received the training to know how to set up condensing boilers to run at their full potential efficiency.

There’s no point in buying an all-singing-all-dancing efficient boiler and then having it installed by a charlatan. You need to choose your installer carefully.

The Heating People are proud to be part of the Heat Geek Elite; because we understand that as engineers; we’re the number one contributor to heating system efficiency, far more than the products selected.

Rest assured that engineers at The Heating People understand emitter sizing; pipe sizing; hydraulic layout and principles; so that we can obtain the highest efficiencies possible.

Choose the right type of boiler for your needs

Once you have an expert installer; the next step towards choosing your energy efficient boiler; is deciding what type of boiler is best for your home and lifestyle.

There are three choices here: a heat-only boiler; a system boiler; or a combi boiler.

And don’t assume that because you currently have a particular type of boiler; it will still be the right one for you.

There’s a good chance that your lifestyle may have changed since your last boiler was installed. And you might have even inherited it with your house!

Choosing the wrong type of boiler can lead to unnecessarily high bills.

We go into detail about each of the different types of boiler in other blogs. But to in a nutshell, your choices here are:

Combi boilers

Diagram of a combi boilerA combi (or combination) boiler takes up very little space in your home. Because it heats water on demand, eliminating the need for any external tanks or cylinders.

Since combi boilers don’t store hot water, they can be efficient because you only ever pay for what you use.

However, combi boilers might struggle if you have a high demand for hot water. Because they are only designed to support one outlet at a time.

Heat-only boilers

Diagram of a heat-only boiler system.A heat-only boiler is sometimes called a ‘conventional’ or a ‘regular’ boiler. These boilers provide your heating and hot water with the use of an additional hot water cylinder; and two cold water tanks in your loft.

Heat-only boilers are ideal for larger homes with high demands for hot water; because they store large quantities of hot water in a cylinder.

Unfortunately, heat-only boilers are generally the least efficient type of boiler; because they have the fewest control options; and they can be wasteful if you don’t use a lot of hot water.

System boilers

Diagram of a system boilerA system boiler supplies your heating and hot water with the use of an additional hot water cylinder. But unlike a heat-only boiler; they don’t need any additional cold water tanks in the loft. They take their cold water supply directly from the mains supply (like a combi).

Similarly to heat-only boilers, system boilers are ideal for larger homes with high demands for hot water; because they too store hot water in an external cylinder.

In terms of efficiency, system boilers are compatible with renewable technologies, such as solar. And they can be installed to low temperature, high efficiency heating – which we get into later on.

Choose the right size of boiler

A boiler next to a boy dressed as a superhero.In addition to choosing the correct type of boiler for your needs; you need to choose the correct size to optimise your energy efficiency.

Boiler size doesn’t mean the physical size of the appliance. But rather how much energy is output by the boiler in terms of heat, measured in kilowatts (kW).

For example, a 35kW boiler uses 35,000 watts (35 kW) of power per hour; to heat the water for your central heating.

People often underestimate the importance that boiler size plays in creating an efficient heating system.

And the key here is that your boiler needs to be ‘just right’. Too big, and you’ll be wasting energy; but too small, and your boiler will struggle to meet your needs. 

Although it was never good practice, it used to be quite common for boilers to be oversized; rather than finding the precise size needed. But this is bad news for energy efficiency.

If you choose a boiler that’s too big; the excess power will cause your boiler to cycle on and off, which wastes energy and money.

Think of it as being a bit like stop-starting in your car. Stop-starting in traffic will use more fuel and will put more stress on your car’s components; than driving at a nice steady speed on a dual carriageway would.

It’s the same for your boiler. Not only that, but the constant stop-starting also prevents your boiler from getting into condensing mode; when it’s at its most efficient.

To find the perfect size of boiler for your home; you need to get a Gas Safe engineer to conduct a heat loss calculation.

For more on what heat loss is, and why it’s important, you might like to read our related blog here.

Choose a boiler with a low minimum output

A diagram showing boiler modulation.Related to choosing the correct size of boiler, you should choose a boiler with a low minimum output.

For example, if you have a 30 kW boiler, the maximum energy output is 30kW; but your boiler will operate within a range up to this, such as 3-30 kW.

The lower the minimum end of the range, the more efficiently the boiler can operate all year round.

Improving the energy efficiency of your heating system

All modern boilers are A-rated for efficiency (although they all offer different features). But there are other things you can do to improve the efficiency of your heating system:

Use heating controls

If you don’t use heating controls alongside your boiler, you’ll be wasting energy.

Research by BEAMA found that having the right heating controls; could save you up to 40% per cent on your energy bills.

According to The Energy Saving Trust (May 2020), based on a typical three-bed semi-detached house; there is a potential saving of £75 a year by installing a thermostat, programmer and thermostatic radiator valves.

And if you’ve read our guide on saving money on your energy bills; you’ll know that simply turning your heating down by 1°C could save you around £80 a year.

But again, what to choose?!

As with boilers, heating controls have advanced significantly in recent years, and there’s a vast array of choices out there.

In the past we largely relied on simple mechanical thermostats in the hallway. But now we can operate our heating from our smartphones. And our thermostats can actually learn our habits, and do everything for us!

We can use intelligent zoning controls, so that we don’t have to waste money heating rooms that we don’t use.

We have weather compensation, load compensation, and flue gas heat recovery. The list goes on…

But what all of these different technologies have in common; is that they are designed to improve our home comfort, whilst saving energy. This not only helps our wallets, but the environment too.

The Heating People will provide you with advice on what heating options would work well with your new boiler; as part of your free survey.

You might also like our blog: Does smart heating save money?

Balance your system

When having your boiler installed, your heating engineer can balance your system to make it more efficient.

Balancing your heating system means optimising the flow of water in the system. So that all of your radiators heat up evenly and give off the right amount of heat.

The idea is to get the water returning to your boiler to be 50 degrees or lower. This allows your boiler to operate in its efficient condensing mode. 

If your system isn’t balanced, some radiators (probably the ones closest to your boiler); will take the bulk of the hot water flow, leaving other radiators with less.

This can reduce your boiler’s efficiency and leave you with some rooms that feel warmer than others.

So, by balancing your system, you’ll improve your home comfort as well as improving your energy efficiency.

Ask your engineer about low temperature heating

We mentioned earlier that system boilers can be installed to low temperature heating systems… Now don’t panic here – we’re not suggesting that you should ask your engineer to make your house cold!

Low temperature heating means that the water flowing around your heating system runs at a lower temperature than usual; whilst still keeping your home at a comfortable temperature.

Generally, the water flowing around your radiators is between 70 °C and 85 °C. But with a low temperature heating system, the water could be as low as 25 °C to 50 °C whilst still keeping your rooms warm

Low temperature heating is much more efficient; because the cooler water allows your boiler to condense properly – as we saw this above with balancing your heating system.

If this is something you’re interested in, you should contact The Heating People today!


With home energy bills set to rise to eye-watering levels, improving the efficiency of your heating system is a must. Choosing an energy efficient boiler and following the tips in this guide can lead to serious money saved.

For tailored advice on finding the best system for your needs, contact The Heating People today.

Useful links

The Heating Hub: Energy saving tips

BEAMA research on heating controls