A more efficient boiler means paying less on your heating bill. 

Fossil-fuel boilers such as oil and gas will always be less than 100% efficient and lose efficiency with age.

Electric boilers do not need to burn any fossil-fuels in your home. They are practically 100% efficient and remain so throughout their lifetime.

Let us explain

Important: click on each link below to find out more about your boiler

Boiler efficiency really matters to both your pocket and planet.

For a new oil or gas boiler which typically works at 91% efficiency, each £1 spent on fuel will include 9p worth of waste gases. And you can see much of this waste as greenhouse gas emissions coming from your property’s heating flue.

Over time, fossil-fuel boiler efficiency will decrease, which we have explained in a little more detail in the section below.

This decline in efficiency means it’s important to replace a fossil-fuel boiler every 10 years or so.

Click the links below to find out more about what’s going on and what you can do. 

Similar to a car’s exhaust pipe, heating flues from a property release greenhouses gases into the air surrounding a home.

What is boiler efficiency?

Efficiency is determined by how much fuel the boiler can convert into useful heat, and how much gets wasted in the process.

Waste gas is disposed of through the property’s heating flue and released into air surrounding the property.

A new oil or gas boiler typically works at 91% efficiency.

This means that although you pay for 100% of the fossil-fuel needed to heat your home, you’ll only feel 91% of this investment as heat.

The rest is made up of waste, including greenhouse gas emissions that negatively contribute to climate change.

Over time the boiler will also become less efficient as the internal parts and technology ages. This means the cost to run the boiler will gradually increase, with many households running boilers at 70-80% efficiency, or less.

This can amount to roughly 30% of your hard-earned cash going out the window.

How efficient is MY boiler at new?  

Why is boiler efficiency important?

Burning less fuel means spending less money – and releasing fewer carbon emissions into the atmosphere.

In the same way as a petrol or diesel car, burning oil or gas to heat your home will produce polluting carbon emissions that need to be released through an external outlet – in this case, a flue. The more fossil-fuel your inefficient boiler needs to burn to reach the right temperature, the more emissions it will produce.

This is why phasing out fossil-fuel heating is a key part of reaching net zero. Having a boiler as efficient as possible in your home is great news for our planet as it will help reduce the volume of carbon emissions impacting the climate crisis.

And if you enjoy being warm at home on a cold winter’s day, an efficient boiler will also heat your home faster.

An efficient boiler helps you;

  • burn less fuel

  • spend less money

  • produce less greenhouse gases

Your heating bills will go up as your oil or gas boiler’s efficiency goes down. 

Which are the most efficient boilers?

Electric boilers

An electric boiler is practically 100% efficient as it does not burn any fuel to produce heat for your home.

The ‘fuel’ needed to heat your home (electricity) arrives on-demand and ready-to-use.

And any small amount of energy lost from an electric boiler will be through operating boiler controls – not greenhouse gas emissions.

That’s why you’ll never see a chimney, heating flue, or any fumes being emitted from a property heated by electric.

Condensing Boilers

If you’re unable to switch to an electric boiler, the next best option is a condensing boiler.

These boilers are far more efficient than a conventional boiler as they recycle exhaust gas through a condensing heat exchanger. This is good news for your pocket, and your property will also release far fewer carbon emissions.

These are available for both gas and oil heating systems.

Electric boilers are practically 100% efficient and remain so throughout their lifetime. 

How to make your heating system more efficient

Insulation is one of the most effective ways of reducing energy wastage and fighting climate change. A boiler will only ever produce enough heat to replace what is lost through the fabric of your building – such as through windows, walls and roofs. 

Here are a few more ways you can help keep your boiler and heating system working at its best.

Annual boiler service:

Having a registered engineer to service your boiler each year will help make sure it is running efficiently, for as long as possible, which will help save you money.

Insulate cylinders and pipes:

Property insulation is one of the most effective ways to keep your home warmer and heating bills down. A quick and inexpensive win is often insulating your hot water cylinder and pipes, if they are exposed copper. Wrapping the cylinder with insulation will keep the water hot for longer and means you won’t have to heat the water up so often. This will reduce how much you need to spend on energy to heat the water.

Run your heating every month (even during the summer):

Running your boiler at least once a month through the summer helps prevent faults developing and pipes/pumps from seizing up. This means that when the chilly months return, you know your heating system is ready to keep you warm.

It’s also worth remembering that the best time to switch to a new heating system is during the spring or summer when you don’t need the heating on.

Bleed your radiators:

Air can make its way into your heating system and cause blockages. This means the top half of the radiators become cooler than the bottom and affects the amount of heat available to heat the space. Bleeding the radiator gives a route out for the air so hot water can circulate right around the radiator and means the system won’t have to work as hard to produce the heat you need.

Keep water pressure topped up:

If the boiler pressure drops, your system will need to use more fuel to heat your home as it has to work harder. You can check the pressure of your boiler on the pressure gauge to make sure it’s set to the boiler manufacturer’s instruction. Boiler pressure can gradually decrease over time, and sometimes can drop suddenly due to a water leak or shortly after radiators have been bled.

Use a smart thermostat:

More control means higher efficiency if used correctly. Smart thermostats such as Nest and Hive help you control and monitor your heating system to help reduce energy wastage. Some systems also track weather conditions and automatically adjust the heating to adapt to your unique home habits.

Fit individual radiator thermostatic valves:

These allow you to vary maximum temperature of each room where the valves are installed. This means rooms you don’t often use can be heated to a lower temperature to help prevent damp and condensation, whilst rooms you use all the time can be heated to a comfortable temperature.

Replace your boiler: if your boiler is around 8-10 years old, it’s worth considering a replacement. Modern boilers are very efficient, and a new boiler can help significantly reduce your heating bills. The best time to switch to an electric boiler is during the spring and summer as it can take some time to complete the installation.

Keeping the heat in is a simple way to reduce energy bills and do your bit for the climate crisis. 

When do you need a new boiler?

It makes no sense to throw out a perfectly good boiler. Until it stops working for you, it’s worth keeping it in good condition and saving up for a good-quality replacement when the time is right. 

The time will eventually come when the boiler needs replacing. Here’s a short list of things to look out for before you make a decision.

Your boiler is over 10 years old

Even if the boiler appears to be working fine, as each year passes gas and oil boilers become less and less efficient. They’ll cost more to run to get the same amount of heat and will produce more greenhouse gas emissions.

How old is my boiler? 

Heating bills are increasing

As with most things, the cost of your fuel is likely to increase year-on-year. But if you’re noticing a significant increase in your heating bills, it’s likely you’re relying on an inefficient boiler that desperately needs replacing.


If you notice any leaking from your boiler, it’s important to contact your engineer as soon as possible to avoid any dangerous or significant damage to your property.

Replacements are hard to find

If you’re hearing that boiler parts are getting harder to come by, that’s a clear message that your boiler is on the way out and can be replaced by a more modern, efficient alternative.


Any banging or gurgling noises from your boiler shouldn’t be ignored as it often means a breakdown is on the horizon.

Regular breakdowns

If you’re constantly topping up the pressure or there seems to always be something wrong with the heating or hot water, the situation won’t get better. It’s worth considering if the money you’re spending getting it fixed could be better spent on a modern, efficient boiler that will save you money over time.

Yellow flame

A fossil fuel boiler should burn with a blue flame. If the flame is yellow, this could be a sign of a carbon monoxide problem which needs to be dealt with urgently by a qualified engineer.

It’s not heating your home

The heating’s on, but no-one wants to be home as it’s freezing cold?

Or you’re always running out of hot water?

It could be a sign your boiler is not doing its job anymore.

Don’t let this be you this winter. Speak to your preferred heating specialist if you’re worried about your heating.

Discover more about electric heating