How Efficient is My Boiler?

June 28, 2022
A woman in a yellow jumper placing her hands on a radiator.

Did you know that around 55% of your energy bill goes on heating your home? And did you know that a percentage of your energy usage is immediately wasted by your boiler?

All boilers in the UK have an energy efficiency rating relating to the amount of energy they use and the amount of energy they lose. Gas Fired boilers are rated from A to G. But what do those letters mean and how do you know whether your boiler is efficient or not?

In the article, we take a look at boiler age, efficiency, heating controls and boiler installation whilst providing some quick energy saving tips that will help your wallet with little to no outlay.

How Efficient is My Boiler?

Boilers are given energy efficiency ratings depending upon how much of the gas they use being converted into heating your home and how much is lost up the flue/exhaust. Modern condensing boilers are advertised as being around 94% efficient which means that 94% of the gas they consume can be put towards heating your home whilst 6% of the gas they use is lost in the process.

If we assume you have an A-rated boiler in your home and take the new average energy bill, post April 2022; £2500 will be spent every year paying for the energy to run your home, £1375 will be spent on heating your home, and £123.75 of that money will be lost in your boiler. Don’t forget that this is the best case scenario!

Boiler Efficiency Ratings

Many old boilers could be rated from B to G.

  • A rated boilers must be 90% efficient or more
  • B rated boilers must be 86-90% efficient
  • C rated boilers must be 82-86% efficient
  • D rated boilers must be 78-82% efficient
  • E rated boilers must be 74-78% efficient
  • F rated boilers must be 70-74% efficient
  • G rated boilers are below 70% efficient

If you have an old backfire boiler in your home it is likely to be only around 60% efficient! Let’s run the numbers again.

A G-rated backfire boiler with 60% efficiency. This means a heating bill of £1375 but only £825 of your bill actually goes towards heating your home! £550 is lost! That’s a HUGE amount of money to ‘lose’ each year. What’s more, in reality your heating bill will probably be a lot higher than £1375 if you want your home to be warm!

How Efficient is My Old Boiler?

Boilers that are 20 years old or younger will have their efficiency rating set out in the installation manual. Boilers older than 20 years typically didn’t have the efficiency rating stipulated in the manual. If your boiler is an older model you may well want to check its efficiency in the Product Characteristics Database (PCDB) which is a register of boiler efficiencies and controls.

How Can I Tell If My Boiler is Efficient?  

Whilst age isn’t the be all and end all, with boilers it does matter. A-rated boilers are called condensing boilers, not to be confused with combi boilers. All boilers manufactured from 2005 onwards will be condensing boilers, whether you have a hot tank in your home or not.

Condensing means that a portion of the heat that was previously lost in the flue/exhaust pipe is now captured and reused by a secondary heat exchanger, making condensing boilers more energy efficient. The by-product of this is water vapor - which is why it’s called ‘condensing’.

A-rated boilers are more efficient, as stated above, but that doesn’t mean they have been installed or used in an energy efficient way.

Whilst old boilers were designed to run at 80 degrees C, newer condensing boilers have been designed to run at 65 degrees C. Frustratingly, most installers know little about energy savings and set new boilers to run at 80 degrees C thereby losing most of the benefits of the condensing mode. So, whilst you may have a 1-year old A-rated boiler it still may be running at 80% efficiency wasting you an additional £151.25 per year!

If your boiler was installed before 2005, it will be 86% efficient at best and that was at the time of manufacture. Whether or not you have had your boiler serviced during that time the efficiency will be slipping further from the 86% as each year passes. Older boilers are less efficient due to natural wear and tear.

With gas prices due to increase a further 42% in October 2022 you may want to explore the option of a new gas boiler before summer ends. Call us to discuss your options.

What’s the Most Efficient Boiler?

At City Warmth we love all things boiler related and are not tied to any one brand. Part of our mission is to install the best new boiler for the home and family needs, whilst keeping the heating bill to a minimum.

Having said that, there are a number of boiler manufacturers beginning to break away from the pack regarding efficiency.  In alphabetical order, to ensure no impartiality, these manufacturers include: Intergas, Vaillant, Viessmann and Worcester.

Whilst other manufacturers do have stand out boilers such as the Alpha Evoke Combi Boiler, the above brands are leading the way with the entirety of their range and offerings.

When considering boiler efficiency we need to look at the official SAP ratings and the headline efficiency ratings, as presented by the manufacturer. We also need to look at their ability to range rate and their minimum output.

Take a look at an example

If you live in a 3 bed semi-detached town house that was constructed from the 1950’s onwards, then the heat loss of your property will likely be no higher than 8kw. Assuming you have a standard size and construction hot water tank in the airing cupboard, your entire household energy requirements will be no greater than 11kw.

If your boiler was installed by one of the 90% of gas safe heating engineers that know very little about energy efficiency, you probably have a 24kw heat only or system boiler powering your home. Just to recap, you only need 11kw but you’re paying to run a 24kw boiler!

If your boiler is made by Intergas, Vaillant, Viessmann or Worcester the likelihood is that you could range-rate it down to 11kw which means it won’t use any more power than 11kw at any time.  It should also have a minimum output of around 4.5kw. Minimum output means that when your boiler is chugging along as your radiators warm it won’t be using any more than 4.5kw of gas.

Always Hire a Gas Safe Registered Boiler Installer

If you’re considering buying a new boiler please ensure your chosen gas safe registered installer;

  • Knows about range rating and minimum outputs
  • Is trained in how to calculate a proper heat loss of your property
  • Doesn’t try to sell you a 24kw boiler
  • Will install manufacturer specific energy saving controls

Some of the new Intergas, Vaillant, Viessmann and Worcester boilers can be range rated and have modulation ratios of 1:19 and minimum outputs as low as 1.9kw! To put that in perspective, the average combi boiler can’t be range rated, has a modulation ratio of 1:4 and a minimum output of 7kw.

If you’re in Brighton & Hove or the surrounding area and you want to chat about how we can get an energy efficient boiler installed in your home, get in touch today. At City Warmth, we don’t just provide background information on the main boiler manufacturers, we give examples of fixed price boiler products you can choose from.

Would a New Boiler Installation be More Energy Efficient?

The short answer is yes, but answering that question in isolation may not paint the full picture.  At the top end of modern condensing boilers you will find boilers that boast 94% efficiency.  Whilst the boiler may be able to achieve that, the heating system it is attached to may not. An energy efficient boiler needs to be installed with energy efficient controls.

As of April 2019, all new combi boilers need to be installed with energy efficient controls that provide either;

  • Flue Gas Heat Recovery
  • Load Compensation
  • Weather Compensation
  • Automation and Optimisation

Whilst there are some third party controls that offer Automation and Optimisation, most other energy efficient controls are manufacturer specific. Thankfully, some of these controls can be retro-fitted to improve the efficiency of existing boiler installations.

As an example:

Having a 94% energy efficient Vaillant Combi boiler installed with a single channel programmer and a separate room thermostat would significantly reduce the efficiency potential to around 82-86%.

Installing a third party wireless programmable room thermostat that offers automation and optimisation with the Vaillant Combi Boiler would bring the boiler efficiency up to around 86-90%.

Installing a Vaillant VRC700 weather compensation unit with the Vaillant Combi Boiler and commissioning it correctly would make full use of the 94% energy efficiency.

Whilst installing a new boiler may well provide you with some savings, those savings could be vastly improved by; installing said boiler with manufacturer specific energy saving controls, commissioning the boiler correctly, cleaning/flushing the heating system properly and balancing the heating system to ensure all radiators get hot together.

Take the time to ask your gas safe installer some questions around this topic and ensure they know what they’re doing. A new boiler installed correctly could recoup the cost of installation within 8 years even when taking the cost of annual servicing into account. A new boiler installed incorrectly may need to be replaced within 10 years, having saved you very little in the meantime!

Boiler Efficiency: Energy Saving Tips

We know that your household bills are rising and we also know that you want to save money where you can. So, here are 5 quick and simple ways that can help you save money on your gas bill from your friends at City Warmth:

  1. Turn the flow temperature on your boiler down to 65 degrees. If you notice no difference in the warmth of your home, turn the flow temperature down to 50 degrees. You’ll be good to leave it there. A HHIC (Heating & Hot Water Council) 2021 report found that households could save between 6 and 8% on their heating bills by simply turning down the boiler flow temperature. TO BE CLEAR, THIS IS NOT THE ROOM THERMOSTAT, THIS IS THE BOILER FLOW TEMPERATURE.
  2. Turn down your room thermostat by 1 degree. The Department of Energy estimates savings of about 1 percent for each degree of thermostat adjustment per 8 hours, and recommends turning thermostats back 7 to 10 degrees from their normal settings, for 8 hours per day, to achieve annual savings of up to 10%.
  3. Turn down the tap hot water temperature on your hot water tank or combi boiler.  Fancy saving up to another 10% on your gas bill here as well? You’re welcome.
  4. Compare energy supplier charges. If your last energy provider went into administration and you’re still with the provider you were automatically moved on to, then shop around. The standing charges with some suppliers can be up to 3 pence per day cheaper, whilst the cost per kw of gas can be up to 2 pence per unit cheaper. 2 pence per unit! Even with so few energy providers left you could still save up to £150 per year just by shopping around. Every little helps.
  5. Get your boiler serviced! And please don’t fall for the £55 summer saver deal you saw on Facebook Ads. Those aren’t real boiler services. They’re safety checks at best and a waste of your time and money. If you want to know more about what a proper boiler service should include and what it will cost, take a look at our blog article on boiler servicing here.

Final Words

We hope you have found this article helpful. As you can tell, the efficiency of your boiler can have a huge impact on your heating bills and the comfort of your home. If you have any questions or you would like some advice, our friendly team would be happy to help. Just give us a call! Also, be sure to check out our blog for more helpful information and expert tips!

The city warmth outlined icon in orange.