Installing an A-rated condensing boiler

Last updated Wednesday 30 April 2008

Ditching your old boiler could save a tonne of CO2

Is your current boiler a star pupil or bottom of its class? Raising your grade from an 'F' to an 'A' means more heat for less money, and a healthy cut in your carbon footprint.

Heating our homes and our water is the biggest energy cost households face each month, yet many people don't know the average boiler is only F-rated. An A-rated boiler can produce the same amount of heat for a fifth less fuel - and CO2.

The best of the modern condensing boilers convert more than 90% of their fuel into heat, compared with a wasteful 72% (or far worse) for the average boiler in UK homes. Depending on the size of your house and the state of your boiler, that could mean an extra 110 a year in your pocket.

Read more below
Photo: Installing an A-rated condensing boiler

Saves about 875kg of CO2 a year per household

289 Bloomers are doing this

CO2 reduction 2 out of 5

Cheapness 5 out of 5

Popularity 3 out of 5

Cost 1500 +

About these ratings

In this article:

How does it work?

Pub Fact

  • The average boiler installed in the 1990s was 20% more efficient than one installed in the 1970s
  • Conventional boilers produce about 60% of all domestic CO2 emissions

A condensing gas boiler differs from a non-condensing boiler in that it has a larger (or second) heat exchanger to scavenge some of the heat that would otherwise escape up the flue.

(Incidentally, a by-product of this process is 'condensate' - water, in other words - which exits your flue in a white plume. But relax - it's steam not smoke.)

For more technical titillation see the Energy Saving Trust website.

Back to top

How will it make a difference?

  • Changing from a low G-rated traditional boiler to an A-rated condensing one could reduce a household's CO2 emissions by over a tonne
  • Making the switch could save 110, about a quarter of the average heating bill. Upgrading your heating controls can save a further 90
  • Across the UK, we could save enough energy to heat 3.7 million homes for a year - the equivalent of all the homes in the West Midlands - or 13 million tonnes of CO2 emissions

It's also worth noting that, although any boiler inspected and serviced regularly should be perfectly safe, most incidents of carbon monoxide (CO) poisoning are caused by old, poorly maintained appliances.

Back to top

What's the debate?

To get the maximum efficiency gain from some condensing boilers, they need to be working in 'condensing mode' - which in practice means heating five or more radiators at full pelt. Nevertheless, condensing boilers are still generally more efficient than 'non-condensing' models, however light or heavy their use.

"Surely this old thing isn't ready for the knacker's yard yet?"

Actually, it's not a bad question. A boiler can live more than 20 years and your brand spanking new A-rated one is still energy-expensive to manufacture, so whether it makes sense to replace it really depends on just how inefficient it is and how much you use it. The older the boiler and the larger and draughtier the house, the more you'll save in emissions and money (especially if you sort out those draughts first!)

Back to top

What's stopping me?

"Why gas? Aren't oil-fired boilers more efficient?"

Yes - and no. While the best oil-fired boilers are a full 6% more energy-efficient than the best gas boiler, they still emit more CO2 overall. This is because oil is significantly more carbon-intensive than gas.

Back to top

How do I do it?

  • Check out the efficiency of your boiler: SEDBUK
  • If your boiler is less than A grade - and getting on a bit - consider installing a condensing gas boiler - or even a biomass heater
  • For a registered installer, contact CORGI
  • For independent professional advice contact the Heating and Hotwater Industry Council
  • See whether you are entitled to a heating grant on the Energy Saving Trust website
  • Practise explaining to your neighbours that the steam plume is not pollution

Back to top

When should I do it?

If your boiler is 10-15 years old, you should certainly consider it. Apart from that, it's best to do it when you're fitting a new kitchen or bathroom, as this will minimise additional cost and disruption.

Back to top


If you like this action send it to a friend

Share this

Back to top


Baz, Shropshire 2009-02-07

I agree with Shaun - the condensing boiler is more efficient. We should be aware that the boiler does not always run in condensing mode, if you have the radiators too hot the return water will not be cool enough to allow condensation to take place. If you really want to burn your gas or oil efficiently, look at co generation. Burn the fuel in an internal combustion engine (spark or compression ignition depending on fuel type), collect the heat and use it in your heating system and the engine will turn a generator to make electricity which you get for free. Obviously there is noise from the engine and you need the room to install it, but it is a well established technology. If you are thinking of using a sterling engine you should know that the thermal efficiency of these machines is quite low, so the heat to electricity ratio is smaller than with an internal combustion engine and you will have less useable electricity.

Shaun, Wombwell, UK 2008-09-09

Updated the boiler when we installed solar water heating. The new boiler is WAY efficient, and heats the water rather than the room the boiler lives in.

Flower representing the 'Installing an A-rated condensing boiler' action

People using this site

4% of Bloomers are doing this action

6% of men in their 40s are doing this action.

Top 3 popular actions that males aged 40-49 are doing

More about actions by people of this age and gender.

Latest actions on Bloom

Latest related BBC News stories

RSS icon | News feeds | View all stories

Related links

Elsewhere on

Elsewhere on the web

Related links open in a new window. The BBC is not responsible for content on external sites.

Browse all actions

Glossary terms used on this page
CO2, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO2 to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO2 is important. Burning fossil fuels releases CO2 into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.
Carbon is the fourth most common chemical element in the universe, and carbon compounds - in other words, carbon chemically combined with other elements - are the basis of all known life forms on earth. Pure carbon appears in many apparently diverse forms, from diamond to graphite to charcoal, but it is much more commonly found in substances such as coal, oil, natural gas, wood and peat that we use for fuel. When we burn these substances to provide energy - either directly in our homes as heat, or in power stations to produce electricity - the combustion process produces 'oxides' of carbon, including the gas CO2.
Condensing boiler
A condensing boiler captures and uses energy contained in the water vapour given off when gas or oil is burned. In a non-condensing boiler this vapour leaves via a heat-resistant gas tube, or 'flue', and its energy is wasted. A condensing boiler cools the combustion gases sufficiently that the water vapour condenses back into liquid and its heat is recaptured. Approximately 10% of the energy value of the fuel is contained in this water vapour, so a condensing boiler converts far more of the fuel's energy into heat.
Draught proofing
Draught proofing is the process of filling in unwanted gaps in the fabric of a building to reduce the heat loss and discomfort they cause. Common sources of draughts are gaps round window and door frames, places where pipes enter the building, ill-fitted floorboards, letter boxes and even keyholes. Materials used include foams, brushes and thin sections of rubber, plastic or metal.
Emissions are the CO2 (and other greenhouse gases) produced by energy use, usually calculated and stated as an annual tally: also referred to as your carbon footprint. Your personal emissions can be direct - such as the gas you personally use to heat your home or the petrol you burn to power your car - or indirect - meaning the energy use that has gone into the products or services you buy. The latter, such as the emissions caused by the manufacture of your new TV, or the packaging your food comes in, are also referred to as embodied emissions.
Kilowatt-hours (kWh)
A kilowatt-hour is an amount of energy equivalent to a power of one kilowatt (a thousand watts) running for one hour. The unit is commonly used on electricity meters. If you know how many kilowatt-hours of energy your household uses, you can translate this into kilograms of CO2 emitted by multiplying it by 0.527. A megawatt hour (MWh) is an amount of energy equivalent to the power of one megawatt (a million watts) running for one hour. Similarly, a gigawatt hour (GWh) is a billion watts for one hour, and a terawatt hour (TWh) is a trillion. While your domestic gas bill will be set out in kWh, the output for a power station, for example, will obviously be expressed in one of these much larger units. navigation


The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.