A boiler with an A-rating is one of the most efficient ones on the market.

To figure out how efficient a boiler is, you have to figure out how much of the fuel used to run it is turned into energy that can be used to heat your radiators and hot water. The boilers that waste the most energy get the lowest rating, while the ones that use the least amount of energy get an A rating.

With this rating system, you can choose a new boiler knowing that it will waste as little energy as possible. When you put in an A-rated boiler, you get two main benefits. First of all, your energy bills go down when less fuel is wasted. During the winter, heating costs make up about 60% of the average home’s gas bill. This means that putting in an A-rated boiler is a good way to save a lot of money. Second, these boilers are better for the environment because you use less fuel to heat your home and make hot water.

Check if you are eligible for funding
Why it’s a good idea to install an A-rated boiler

Spend less on heating costs

Less energy is wasted

Lessen your impact on the environment

Is my home eligible for a Boiler Upgrade?

Boiler Upgrades FAQ’s

How well does my old boiler work?

As your boiler gets older it will become less and less efficient.

The average gas bill for a home is between £750 and £1000 – figures that are constantly rising. This depends on the size of your home, how old your boiler is, and how well it works.

Most boilers in use in the UK are only about 80% efficient because many of them are too big and old. Boilers that are more than 25 years old may only be 60% efficient, which can really drive up the cost of fuel.

Why should I replace my old boiler with a new one?

Even if your boiler is still working after 15 years, you should think about getting a new one because its efficiency will have gone down, which will make your fuel bills go up, and a new boiler will save you money. The Energy Saving Trust says that a boiler that saves energy could save you up to £445 a year. 

What is the best size of boiler to use?

Once you know what kind of boiler you need, the next important question is how big it needs to be.

In terms of how well it works, the size of the boiler is its heat output, which is measured in kilowatts (kW). When the boiler is turned on, it will use more energy the more heat it can put out.

Most of the time, a bigger house with more radiators and bathrooms will need more heat than a smaller house.

But if you get a boiler that’s too big for your home, you’ll use a lot more energy to heat it than you need to, which will lead to higher bills and more carbon emissions than needed.

How to explain boiler efficiency ratings

Once you know what kind and size of boiler you need, you can use the energy efficiency ratings to narrow down your choices and choose the most energy-efficient one.

ErP energy rating

The European energy label ErP, which stands for “Energy-related Products,” is used to rate the efficiency of all modern boilers (introduced in 2015). It gives boilers grades from A+++ to F, with A+++ being the best.

Combi boilers have two ratings: one for heating the space (shown by the letter under the radiator symbol) and another for heating the water (the letter under the tap symbol). The space-heating component measures how well the boiler heats your radiators. The water-heating component measures how well the combi boiler heats your hot water for showers and taps.

Only the space-heating part of the ErP label is on boilers that only heat and boilers that only heat water.

On the ErP label, it also says how loud the boiler is in decibels (dB). The boiler will make more noise the higher the number is. Lastly, it shows how much heat the boiler puts out in kW.

On this label, almost all modern gas condensing boilers sold in the UK get an A rating. In 2018, the UK government also passed the “Boiler Plus” law, which says that all boilers in England must have an ErP efficiency of at least 92% (or be “A-rated”). This is great news because it means that almost any new boiler will work well.

If you want to know more about how the efficiency of one boiler compares to another, you might find the SEDBUK 2009 efficiency rating more useful.

What are SEDBUK ratings?

SEDBUK stands for Seasonal Efficiency of Domestic Boilers in the UK. It is a way to compare and classify boilers based on how well they turn fuel into heat.

SEDBUK ratings used to be shown on labels as a letter, but these labels have been taken off to avoid confusion with ErP labels, which use similar ratings but are based on different principles.

There are two types of SEDBUK ratings, called SAP scores, that you should look for when you buy a boiler.

SAP winter efficiency: This is measured by a separate lab and shows how well the boiler heats the house and makes hot water. On this measure, modern condensing boilers aren’t too different from each other.

SAP hot water efficiency: This number shows how well your boiler heats water for your taps. This is where boilers tend to differ the most, so if you want the most efficient one, this is the number you should focus on.

The exact ratings for each boiler’s winter efficiency and hot water efficiency can be found in the “Tech Specs” section of our boiler reviews, under the headings “Efficiency” and “Hot Water Efficiency,” respectively.

What funding is available?

ECO4 funding is available for boiler upgrades in certain areas, check if you’re eligible for ECO scheme boiler upgrades here.


Boiler Grant


What is a free boiler grant?

ECO grants are funds being provided to help individuals with the lowest incomes insulate their homes, as well as those who live in the least energy-efficient homes or the lower council tax bands.

How do grants for boiler upgrades work?

First, eligibility is determined by a number of factors including household income, EPC rating and whether or not you are receiving any current government benefits. Residential Energy Services then work to determine suitable energy efficiency measures for your home. We also work with a trusted network of partners to help ensure those measures are delivered correctly.

How do I apply for a boiler grant?

Contacting Residential Energy Services is the quickest and most straightforward way to find out if you qualify, compile your eligibility criteria and approach energy providers to obtain boiler grant support.

How much can I get from an ECO grant?

Under the ECO4 scheme, free home energy efficiency upgrades are available to eligible homes. The awarding of grant funding is entirely dependent on determining the right measure for your home at this time.

How much money is available for in ECO grants?

The ECO4 scheme, which is expected to run until March 2026, expects to deliver up to £4 billion in energy efficiency and heating measures.

Who pays for boiler upgrades to my home?

The Energy Company Obligation is a government scheme deployed by energy suppliers who fund energy efficiency measures for your home, delivered by ECO approved installers.

Who decides what measures I’m suitable for?

It is ultimately the decision of the energy supplier to determine which measures are best; however, a home energy assessment with Residential Energy Services can make this process more accurate, relevant and efficient, to make sure you’re getting exactly the support you need.

Boiler Grant Eligibility


Is the ECO scheme means tested?

If you claim means tested government benefits it is likely that the ECO scheme is for you. Check your eligibility before consulting with your energy supplier.

What benefits do I need to receive to get ECO funding?

If you receive at least one of the following government benefits the energy company obligation should be able to support you with new energy efficiency measures:

  • Child Benefit
  • Pension Guarantee Credit
  • Income-related Employment and Support Allowance (ESA)
  • Income-based Jobseeker’s Allowance (JSA)
  • Income Support
  • Tax Credits (Child Tax Credits and Working Tax Credits)
  • Universal Credit
  • Housing benefit
  • Pension credit saving credit

I live in a rural area, am I eligible for ECO funding?

If you have an EPC rating of D or below, and fall within any of the means tested benefits listed above, you should be eligible for ECO4 funding. Check your eligibility with Residential Energy Services.