Heating and hot water accounts for over half of what you spend in a year on energy bills, so an efficient boiler makes a big difference.
All modern, well-maintained boilers burn their fuel efficiently, but they inevitably lose some heat in the hot gases that escape up the flue (a pipe used to extract fumes and supply fresh air to the boiler).
Modern boilers are more efficient than older boilers for several reasons, but their main advantage is that they are ‘condensing’. A condensing boiler recovers more heat from the exhaust flue gas and uses it to heat the central heating water, making it more efficient than older boilers.
Things to consider
If it’s time to change your boiler, or if you’re thinking ahead for when it needs to be replaced, you’ll need to decide what type of heating system is right for you. Now might be the right time to switch to a low or zero carbon emission heating system.
As part of the UK Government’s plan to reach net zero carbon emissions by 2050, fossil fuel heating systems are likely to be phased out over time. This will start with a ban on gas and oil boilers in new homes from 2025, and we expect to see more and more existing homes switch to a low carbon heating system, such as a heat pump.
There are several things to consider when deciding what type of heating system is right for you:
If you have a mains gas connection, a modern, condensing gas boiler has typically the lowest running costs to provide heating and hot water. Our average fuel prices show gas to be the cheapest heating fuel per kWh, compared to oil, electricity, LPG and house coal.
If you’re looking to lower your carbon emissions, you should consider a form of low carbon heating such as a heat pump, which could also reduce your running costs depending on the type of system and fuel you’re replacing.
Gas and oil boilers are either ‘system’ boilers, which have a separate hot water cylinder to store hot water, or ‘combi’ boilers, which heat hot water on demand and don’t require a hot water cylinder.
A system boiler is more efficient than a combi boiler at producing hot water, however heat is lost from the hot water cylinder over time. A combi boiler could be more efficient overall, although this depends on several factors such as how many people there are in the property and whether you are likely to install solar panels in the future. Having a hot water cylinder allows you to store energy from a solar system – if you are not able to install solar panels then this might influence your decision.
Choosing the right boiler for you will depend on different things, including:
Your hot water usage. Large families using lots of hot water are likely to be better off with a system boiler, whereas smaller households using less hot water may be better off with a combi boiler.
Space in your home. Combi boilers don’t need hot water cylinders, and therefore require less space.
Compatibility with solar water heating. If you’re thinking of installing solar water heating, it’s simpler for them to work with system boilers, although combi boilers can be adapted too.
Being heat pump ready. Most heat pumps work with a hot water cylinder, so if you get rid of your existing cylinder and fit a combi boiler, keep in mind that the cylinder may need to be put back in if you switch to a heat pump in the future.
How to identify condensing boilers
Since 2005, virtually all gas boilers that have been fitted in the UK are more efficient, condensing boilers.
Your boiler will be a condensing boiler if:
The flue is made of plastic. If it’s made of metal, it’s unlikely to be a condensing boiler.
The boiler has a plastic pipe coming out of the bottom, through the wall and into a drain.
If it’s a gas or LPG boiler that was installed after 2005, or an oil boiler installed after 2007.
Improve your central heating system
It’s worth considering whether you can improve your central heating system by making one or more adjustments to your heating. These include:
There is a wide range of heating controls available that will help your heating system work more efficiently and keep your bills down. Find out which thermostats and controls might be appropriate for your system.
Some of the heat generated by your boiler escapes through the flue. Passive flue gas heat recovery systems capture some of this lost energy and use it to heat your water, making your heating system more efficient and saving you money.
It’s not usually practical to fit a new flue gas heat recovery system to an existing boiler installation. However, if you are fitting a new boiler, you can choose a model with flue gas heat recovery incorporated into the design, or you can ask your installer to fit a separate heat recovery device along with the boiler.
Hot water cylinders
New hot water cylinders are factory insulated to help keep your hot water at the right temperature for longer. They play an important role in supplying you with readily available hot water, so it’s important that they are fully insulated to prevent heat escaping.
If you have an old cylinder, you could save around £35 a year by topping up the insulation to 80mm. Alternatively, if you are replacing your cylinder, you can save energy by making sure the cylinder is no bigger than you need it.
Corrosion in an older central heating system and the build-up of scale and sludge (rust) can reduce the effectiveness of the radiators, and the heating system.
Using a chemical inhibitor will decrease the corrosion rate and prevent the build-up of sludge and scale, thus helping to maintain efficiency of the system. Inhibitors should be refreshed or replaced whenever the heating system is drained during maintenance work or boiler replacement.
Building regulations encourage the use of magnetic filters to remove rust from the heating water. If your boiler is replaced, or swapped for another type of heating system, your plumber should fit a magnetic filter near the boiler if none is present.
Costs and savings
Replacing a gas boiler
The costs for replacing a boiler will vary, but a straightforward gas boiler replacement plus thermostatic radiator valves will typically cost about £4,000.
Replacing an oil boiler
The costs for replacing a boiler will vary, but a straightforward oil boiler replacement plus thermostatic radiator valves will typically cost about £4,700.
England, Scotland and Wales
Finding an installer
It’s worth getting three quotes from different installers to ensure you get the best value for money.
Your registered installer will ensure that your system complies with current building regulations and will make sure you get all the documentation to prove this. Keep these documents safe as you will need them when you sell the property.