Boiler Efficiency Ratings: The Ultimate Guide

Discover everything you need to know about boiler efficiency ratings, how to improve your boiler's efficiency, and when to consider a replacement.

When it comes to heating your home, understanding boiler efficiency ratings is key to managing your energy consumption, reducing your carbon footprint, and saving money on your energy bills.

With so many options on the market, choosing the most energy-efficient boiler for your needs can seem overwhelming.

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This guide walks you through everything you need to know about boiler efficiency ratings, including how they work, what they mean, and how you can ensure your boiler operates as efficiently as possible.

What is a boiler energy efficiency rating?

A boiler energy efficiency rating is a measure of how effectively a boiler converts fuel into heat. This rating is expressed as a percentage and indicates the amount of energy that is converted into heat versus the amount of energy lost in the process.

For example, a boiler with a 90% efficiency rating converts 90% of the fuel it consumes into heat, with the remaining 10% lost through the flue or other inefficiencies.

In the UK, boilers are rated on an A to G scale, with A-rated boilers being the most efficient (90% efficiency or higher) and G-rated boilers being the least efficient (below 70% efficiency).

Modern condensing gas boilers, which are designed to be more energy-efficient, typically have A-ratings, making them an excellent choice for homeowners looking to reduce energy consumption and lower their heating bills.

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What are SEDBUK efficiency ratings?

From 1999 to 2015, boilers were ranked on the SEDBUK scale, which stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’.

From 1999 to 2015, boilers were ranked on the SEDBUK scale, which stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’.

Although SEDBUK 2009 and 2012 were replaced in 2015 by the Energy-related Products Directive (ErP) many manufacturers still refer to SEDBUK because it provides a more detailed efficiency rating.

What's the ErP directive?

The Energy-related Products (ErP) Directive is a European regulation designed to improve the energy efficiency and environmental impact of energy-related products, including boilers. Under the ErP Directive, boilers must meet certain energy efficiency standards.

Boilers covered by the ErP Directive are required to have an energy label that clearly shows their efficiency rating on a scale from A+++ (most efficient) to G (least efficient). This label also provides information about the boiler's heating output and noise levels, helping you to make informed decisions when buying a new boiler.

The ErP Directive aims to reduce carbon emissions and promote the use of more energy-efficient products, ensuring that consumers have access to heating systems that not only save money but also help protect the environment.

Nearly all modern gas condensing boilers available in the UK get an A rating on this label. Additionally, in 2018, the UK government introduced 'Boiler Plus' legislation, which requires all new boilers in England to have a minimum ErP efficiency of 92%, or 'A-rated'.

How can I make my boiler run more efficiently?

Even the most energy-efficient boiler can waste energy if it's not properly maintained or used incorrectly. Here are some tips to help you make your boiler run more efficiently:

1. Regular servicing: Schedule an annual boiler service with a Gas Safe registered engineer to ensure that your boiler is operating efficiently and safely. Regular servicing can identify potential issues before they become major problems, helping to maintain your boiler's efficiency. Find out what a boiler service includes and how long a boiler service takes with our helpful guides.

2. Bleed and balance your radiators: If your radiators aren't heating up evenly, they may have trapped air inside. Bleeding your radiators removes this air, allowing hot water to flow more efficiently and improving the overall performance of your heating system. Additionally, you can balance your radiators to ensure that heat is distributed evenly throughout your home, which can further enhance the efficiency of your heating system. For information on how to balance your radiators, check out our full guide.

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3. Install a smart thermostat: A smart thermostat can help you better control your heating, ensuring that your home is only heated when necessary. By programming your heating schedule and adjusting temperatures remotely, you can reduce energy wastage and save money on your heating bills.

4. Use thermostatic radiator valves (TRVs). TRVs allow you to control the temperature of individual radiators, reducing the heat in rooms that aren't being used while keeping other areas warm. This can help reduce your overall energy consumption.

5. Insulate your home: Proper insulation reduces heat loss, meaning your boiler doesn't have to work as hard to maintain a comfortable temperature. Insulating your loft, walls, and floors can make a significant difference in your home's energy efficiency.

Should I replace my boiler?

Replacing an old boiler with a new, A-rated condensing boiler can result in significant energy savings and lower heating bills. But how do you know when it's time to replace your boiler?

  • Age of the boiler: Boilers typically have a lifespan of 10-15 years. If your boiler is approaching or exceeding this age, it may be time to consider a replacement, especially if it has a low efficiency rating.
  • Frequent breakdowns: If your boiler requires frequent repairs, the cost of these repairs can add up quickly. Investing in a new boiler may be more cost-effective in the long run.
  • Rising energy bills: If you've noticed a steady increase in your energy bills, despite not changing your usage habits, your boiler's efficiency may be declining. A new, energy-efficient boiler can help bring your bills back down.
  • Noisy operation: Older boilers that make unusual noises, such as banging or whistling, may be struggling to operate efficiently. This could be a sign that your boiler is on its last legs.
  • Inconsistent heating: If some rooms in your home are consistently colder than others, or if your boiler takes a long time to heat up, it may be time for an upgrade.

Here's how much you could save on your fuel bill in a gas-heated home in England, Scotland, and Wales when replacing an old gas boiler with a new A-rated condensing boiler with a programmer, room thermostat, and thermostatic radiator controls:

ErP rating of old boiler

Efficiency

Detached house

Semi-
detached house

Terraced house

Flat (mid-floor)

D

78 – 82%

£265

£215

£180

£80

E

74 – 78%

£320

£240

£200

£90

F

70 – 74%

£410

£270

£225

£100

G

<70%

£580

£385

£320

£145

Source: Energy Saving Trust (January 2024)

If you're considering replacing your old boiler with a more modern one, booking with a local JustFix heating and gas engineer can ensure a smooth installation.

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How to choose the most energy efficient boiler

When choosing a new boiler, energy efficiency should be one of your top priorities. Here's what to consider:

1. Boiler type

Combi boilers are generally more energy-efficient than conventional boilers because they provide hot water on demand without the need for a separate hot water cylinder. However, the best choice depends on your home's specific needs.

2. Boiler size

The size of your boiler should match the heating demands of your home. An oversized boiler can waste energy, while an undersized boiler may struggle to heat your home effectively. Consult a heating engineer to determine the correct size for your home.

3. Energy efficiency rating

Look for boilers with an A-rating or higher on the ErP scale. These boilers are designed to operate efficiently, reducing your energy consumption and lowering your heating bills.

4. Brand and model

Some boiler brands and models are known for their reliability and efficiency. Research different options and read reviews to find a boiler that meets your needs.

5. Features

Modern boilers come with a range of features designed to improve efficiency, such as modulating burners, weather compensation, and smart controls. These features can help you save even more energy.

What size boiler is the most energy efficient?

The most energy-efficient boiler size depends on the size of your home and your heating needs. As a general rule, larger homes with more radiators and bathrooms will require a larger boiler, while smaller homes can get by with a smaller unit.

To determine the correct boiler size, consider the following:

  • Number of radiators: The more radiators you have, the larger the boiler you'll need to heat your home effectively.
  • Number of bathrooms: Homes with multiple bathrooms may require a larger boiler to provide sufficient hot water for simultaneous use.
  • Insulation: Well-insulated homes require less heating, so you may be able to opt for a smaller, more energy-efficient boiler.
  • Hot water demand: If your household turns on the heating and hot water a lot, a larger boiler may be necessary to meet your needs without compromising on efficiency.

Sustainable energy alternatives

New gas boilers will not be allowed to be sold from 2035 onwards (pushed back from 2025) and it's likely that in the future many of us will be heating our homes with renewable heating alternatives.

If you're looking to reduce your carbon footprint and make your home more sustainable before then, consider these energy alternatives to traditional gas boilers:

  • Heat pumps: Heat pumps are an energy-efficient alternative to boilers, using electricity to extract heat from the air or ground and transfer it into your home. They are particularly effective in well-insulated homes and can significantly reduce your carbon emissions.
  • Solar thermal panels: Solar thermal panels use the sun's energy to heat water, which can then be used for your central heating and hot water needs. While they can't completely replace a boiler, they can reduce the amount of energy your boiler needs to use.
  • Electric central heating: Electric boilers are an alternative to gas boilers, using electricity to heat water for your radiators and taps. While electricity is typically more expensive than gas, electric boilers are more efficient and can be powered by renewable energy sources.

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FAQs

What is a condensing boiler?

A condensing boiler is a type of boiler that is designed to capture and reuse heat that would otherwise be lost through the flue. This makes them more energy-efficient than non-condensing boilers, helping you save money on your energy bills.

What are the benefits of a smart thermostat?

A smart thermostat allows you to control your heating remotely, schedule heating times, and monitor your energy usage. This can help you reduce energy wastage and lower your heating bills.

What is the most energy-efficient type of boiler?

Condensing boilers are the most energy-efficient type of boiler available today, with efficiency ratings of 90% or higher. They are designed to recover and reuse heat that would otherwise be lost through the flue.

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