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17 Feb 2022

What type of boiler should your next one be?

Many of us our trying to live more sustainably, and a key way to do that is to reduce our heating carbon footprint in the home. We outline your likely options next time you need to replace your boiler, from a more efficient gas boiler to a heat pump
hand adjusting boiler settings

The writing is on the wall for gas boilers; from 2025, they won't be allowed at all in newly-built homes. The exact date for their phase out from existing homes is yet to be confirmed, but there will come a point when buying a new gas boiler to replace an old one simply isn't an option.

That point is still quite some time away, though. So, given the typical 10 to 15-year lifespan of most gas boilers, a like-for-like replacement will still be an option for most people next time they need a new boiler.

But with the transition to net zero underway, more of us will be considering opting for a more sustainable alternative sooner rather than later. In some cases, your next boiler replacement won't even be a boiler at all.

Read on to find out more about the options that are available now, or might be developed over the next decade. We explain how they work, the pros and cons of each, and the types of home they're most suitable for.

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1. A heat pump

air source heat pump

According to the government's Heat and Buildings Strategy, it expects heat pumps to play a major role in the future of heating in the UK.

When installed in a well-insulated home, a heat pump can run extremely efficiently and use very little electricity.They can be installed in less well-insulated homes too, but you may need larger radiators and a more powerful heat pump, which could cost more to run.

The cost of buying and installing a heat pump typically ranges from £7,000 to £13,000 for an air source heat pump, and £14,000 to £19,000 for a ground source heat pump, according to the Energy Saving Trust. This is considerably more expensive than a gas boiler, but there will soon be grants available to help with the cost (see below), and they're a much more environmentally-friendly way of heating your home than traditional gas boilers.

How do heat pumps work?

Heat pumps work on the same principle as fridges. They draw heat from the ground or air and use a compressor to boost it to a higher temperature.

This heat is transferred by an electrical pump to your radiators, or other heat emitters (underfloor heating, for example), to warm your home.

The two main types are ground source heat pumps, which take their heat from the ground, and air source heat pumps which (surprise surprise) take the heat from the air.

Air source heat pumps tend to be cheaper and less disruptive to install. On the other hand, ground source heat pumps tend to be more efficient over the year, as the ground temperature is more consistent.

Pros and cons of heat pumps


  • No carbon emissions from your home Unlike gas boilers, heat pumps themselves produce no carbon emissions. However, they're powered by electricity, meaning heat pumps aren't a completely zero-carbon form of heating unless the electricity they use comes completely from renewable sources.
  • Energy-efficient heat pumps produce more heat energy than the electricity energy used, making them more energy-efficient than other heating systems. Their efficiency is often expressed as 'Seasonal Coefficient of Performance', and usually ranges from 2.5 to 4.0 depending on the model and time of year.
  • In some cases, running costs can be comparable with gas or even lower Analysis by the Regulatory Assistance Project claims a heat pump operating at an average annual efficiency of 3.0 or higher will cost the same (or possibly less) to run as a gas boiler. To achieve this, you'll need a well-insulated home and to have a high-quality heat pump installed properly by a Microgeneration Certification Scheme certified installer.


  • Require a well-insulated home to run most efficiently If you live in a poorly-insulated property, a heat pump may not heat it as effectively as a gas boiler would.
  • High installation costs There's no getting around the fact that heat pumps are currently expensive to install. Government grants (see below) will also help make some installations competitive with gas boilers, though that's only really the case if your home doesn't need any extra upgrades (such as insulation improvements or larger radiators).
  • No guarantee of lower running costs While heat pumps are more efficient and use less energy than gas boilers, the price of electricity is currently very high compared with gas, which may cancel out the benefit. So, in the short-term at least your energy bills may increase - especially if you have an efficient gas boiler and/or a poorly-insulated home. The price of electricity may come down in the future, but it is an issue right now.
  • Need indoor and outdoor space You need space to house the external units (and lay the underground pipework if it's a ground source heat pump) and space indoors for a hot water cylinder.

Is my home suitable for a heat pump?

If you're considering a heat pump, you should have a MCS-certified (Microgeneration Certification Scheme) installercarry out an assessment on your home before committing to anything. But, as a rule of thumb, a heat pump is more likely to be suitable if:

  • Your home has suitable outdoor space, and enough space indoors for a hot water cylinder without additional building work
  • Your home is already energy efficient, or you have the funds to be able to make insulation or heating system improvements alongside a heat pump installation.

Grants to install heat pumps: the Boiler Upgrade Scheme

The high upfront costs may put many people off installing heat pumps, especially in a home with an existing heating system that works perfectly well.

However, a new government grant, dubbed the Boiler Upgrade Scheme, means homes in England and Wales can receive a voucher worth up to £5,000 towards the cost of an air source heat pump, or £6,000 for a ground source heat pump.

This would reduce the cost of a £10,000 air source heat pump installation to £5,000, for example. Your MCS-certified installer must apply for a voucher for the grant on your behalf.

The scheme is expected to launch later this year and has a budget of £450m over three years. This is only enough for around 90,000 homes in total - so it's likely to run out quickly.

This grant is aimed at well insulated homes: you will need a valid energy performance certificate (EPC) with no recommendations for loft or cavity wall insulation.

If you live in Scotland, you can get a £2,500 loan plus up to £7,500 cashback towards a heat pump installation through Home Energy Scotland.

The price of heat pumps is expected to fall over the coming years, but if your boiler needs replacing, these grants could make a heat pump a more affordable, and sustainable, choice right now.

For more detail on how heat pumps work, and if your home is suitable head to our expert guides on ground source heat pumps and air source heat pumps

2. An electric boiler

Electric boiler

An electric boiler is a similar size (or sometimes a tad smaller) to a gas boiler, and is likely to have comparable costs for buying and installing the boiler itself (a new combi-boiler installation will typically cost around £2,500).

If you're looking to reduce your carbon footprint sooner rather than later, and a heat pump isn't currently viable, an electric boiler could be a more environmentally-friendly option than a traditional gas boiler.

How do electric boilers work?

Electric boilers work by passing electric current through a heating element to heat your water, rather than burning gas. They essentially operate like a big kettle (though they don't boil the water!)

As with gas boilers, you can choose between heat-only or system boilers (that require water tanks to store hot water), or combi boilers (that heat your hot water on-demand).

However, the maximum power output of electric boilers is typically lower than gas boilers, and your home may require expensive electrical upgrades to cope with the increased demand an electrical boiler will make on your electricity supply. These factors mean they won't be suitable for every home.

Before considering a switch, get a qualified engineer who works with electric boilers to carry out an assessment of your home.

Pros and cons of electric boilers


  • No carbon emissions from the boiler Like heat pumps, electric boilers themselves emit no carbon, and are a more sustainable choice than gas boilers. However, also as with heat pumps, they can't be an entirely carbon-free choice until the electricity that powers them comes entirely from renewable sources.
  • Very efficient compared with gas boilers They waste less energy than gas and oil boilers, claiming to be nearly 100% efficient.
  • Can be placed almost anywhere in the home They don't need a flue or gas pipe, so aren't restricted to being placed on an exterior wall as gas or oil boilers are.
  • Installation costs can be equivalent to a gas boiler If your home's electrical wiring doesn't require an upgrade, then installation costs will be similar to that of a gas or oil boiler.


  • You may need to pay to upgrade your home's electrical infrastructure An electric boiler needs to suit your home's electricity supply. If you need a bigger boiler than your existing infrastructure can cope with, this can dramatically increase installation costs.
  • High running costs Electricity is more expensive per unit of energy (kWh) than gas, so running an electric boiler is likely to increase your heating bills compared with running a gas model. The price of electricity vs gas may change in the future, but it is an issue right now.
  • Less efficient than heat pumps While they're more efficient than gas boilers, electric boilers are less efficient than heat pumps and so will cost more to operate.
  • May not be suitable for larger homes Electric boilers typically have lower maximum outputs than gas and oil, so may struggle to meet the higher heating demands of larger homes.

Is my home suitable for an electric boiler?

You should always seek the advice of a trusted local engineer when choosing the best heating system for your home, but in general an electric boiler is more likely to be a option to consider if:

  • Your home is off the gas grid and you're looking for a low-carbon replacement to an oil boiler
  • You want to make a more environmentally-friendly heating choice, but your home isn't suitable for a heat pump (for example if you don't have suitable outdoor space)
  • You live in a high-rise building where an electric boiler could be easier to install and service than a gas boiler.

For even more advice head to our expert guide on electric boilers

3. A more energy-efficient gas or oil boiler

Gas boiler controls

While all homes will eventually transition to low carbon heating systems, for many the alternatives are currently impractical, prohibitively expensive, or still at too-early stages of development.

But sticking with a gas or oil boiler next time round doesn't mean you can't improve your home's carbon footprint - and potentially save money in the process, if an old, inefficient boiler is pushing up your heating bills higher than they need to be.

Current Boiler Plus regulation means all gas boilers sold in England are at least A-rated for efficiency (which means they're at least 92% efficient).

While this rule doesn't apply to Wales, Scotland or Ireland you should still go for an A-rated boiler - keeping your heating efficient and bills as low as possible.

Having said this, all modern boilers are basically as efficient as each other, so your main priority should be choosing the right size of boiler for your home.

Too small (in terms of power output), and it won't heat your home well enough; too big, and you'll be using far more energy than you need to be.

A good heating engineer will be able to recommend the best size of boiler for your home. Head to Which? Trusted Traders to find a reliable local engineer or plumber.

Pros and cons of gas and oil boilers


  • Reasonable installation costs Replacing your current boiler for a similar model will cost around £2,500 for a gas boiler and £3,200 for oil (according to the Energy Savings Trust). For many this will currently be the most affordable option.
  • Typically lower running costs than electrical heating Despite unprecedented increases in the price of energy, gas is still around four times cheaper than electricity, currently making it the most affordable fuel to heat your home in most cases.
  • Familiarity 85% of UK homes are connected to the gas grid, and 1.1 million use oil. Having a gas or oil boiler in the home is a known quantity.


  • Even if more efficient, modern gas boilers still release carbon With 17% of UK carbon emissions coming from heating in the UK, upgrading to a more efficient gas boiler isn't going to get us very far along the road to net zero.
  • Not a future-proof solution Following on from the point above, all homes will eventually need to switch to a low carbon system. If you're in the fortunate position to be able to switch to a heat pump today, you may wish to make the switch now and not have to worry about it later down the line.

How much you could save on your bills by switching to a new condensing boiler

Oil boiler

There's an old saying: if it ain't broke, don't fix it. But even if an old boiler is still plodding along, that doesn't mean it's not worth replacing it.

If you haven't had a new boiler since 2005, or if the flue on your boiler isn't made of plastic, then there is a strong possibility it's an inefficient 'non-condensing' boiler.

All modern boilers are 'condensing', which means they recycle some of the heat that a non-condensing boiler would waste to heat water returning from your central heating system.

A condensing boiler is typically 25% more energy-efficient than an old non-condensing model, and so will mean lower heating bills - and lower carbon emissions to boot.

In fact, switching from an old boiler to a new A-rated condensing boiler with a programmer, thermostat and thermostatic radiator valves could save you anywhere from £50 to £365 a year on your heating bill (Energy Savings Trust, November 2021).

Get a new boiler from a Best Buy brand to ensure it's reliable and will work efficiently for years to come - read our Best Buy boiler reviews

What about hydrogen boilers?

Hydrogen boiler

Hydrogen boilers have been getting a lot of attention recently, despite not actually being available to buy yet.

The government has yet to decide how big a role hydrogen will play in the future of heating in the UK (it's due to make its decision in 2026), but it's anticipated that so-called 'hydrogen-ready boilers' may start appearing on the market in a few years. Hydrogen-ready boilers can cope with being powered by either traditional methane gas or hydrogen, so will be good to go as and when hydrogen becomes available as a fuel .

While cost is still a relatively unknown quantity, if there is significant demand for hydrogen boilers, it's expected that purchase and installation costs will be on a par with gas boilers.

How will hydrogen boilers work?

Hydrogen boilers will work in almost exactly the same way as traditional gas boilers; they'll just burn hydrogen instead of natural gas. Unlike natural gas, burning hydrogen generates no carbon emissions - though the production of the hydrogen itself isn't always carbon-free, as we explain in the cons of hydrogen boilers, below.

Hydrogen-ready boilers can run on natural gas until a switch over to hydrogen happens, at which point an engineer would come and carry out a small service to switch the boiler over to run on 100% hydrogen.

Pros and cons of hydrogen boilers


  • Familiar technology Hydrogen boilers will be easy for homeowners to understand and use, as they work in the same way as gas boilers.
  • Low disruption installations A hydrogen boiler can be easily installed into any home that currently has a gas boiler; hydrogen-ready models can run on either type of gas, so can be installed at a point that's convenient for homeowners.
  • May be the best choice for less energy-efficient homes Hydrogen boilers can more effectively heat poorly-insulated homes compared with heat pumps, so could provide homes with a low-carbon option that doesn't mean paying for expensive insulation upgrades at the same time.


  • There are unanswered questions The role that hydrogen should play in heating homes hasn't yet been decided. This uncertainty might affect things such as the cost of hydrogen (or hydrogen-ready) boilers, and how soon manufacturers invest in their development.
  • Hydrogen production isn't carbon-free While burning hydrogen to provide heat doesn't create carbon emissions, certain methods of producing hydrogen do release carbon. Truly green hydrogen is possible, but it's expensive and needs 100% renewable electricity.
  • Burning hydrogen in air produces other pollutantssuch as nitrogen oxides. It's possible to control these and keep them to a minimum, but legislation needs to be put in place to ensure these controls exist in all hydrogen boilers.

For more information on what heating with hydrogen will look like, head to our expert guide on hydrogen boilers

What about heat networks?

graphic illustration of heat network

Alongside heat pumps, the government's Heat and Buildings Strategy expects that heat networks will play a significant role in heating UK homes in the future, especially in certain areas.

What is a heat network?

A heat network consists of a centralised, large-scale heating system that supplies heating to multiple homes.

Heat networks that supply heating to just one building (such a block of flats) are known as communal heat networks, while ones that supply to multiple buildings are known as district heat networks.

Currently 3% of the UK's heat supply comes from heat networks, but the government plans to increase this to around 20% by 2050.

Pros and cons of heat networks

While most existing heat networks run on gas, they are compatible with a range of heating systems (large ground-source heat pumps or hydrogen boilers that are installed nearby and are big enough to power several buildings, for example) and so can easily be converted to low-carbon energy in the future.

Connecting more homes to heat networks also helps heat homes more efficiently, as a single large heating system can have economies of scale compared with every home having an individual heating system.

Heat networks also have the space for water tanks and other storage solutions to be placed near the heat source, allowing them to store thermal energy. This could reduce demand on the grid during peak times, and reduce the overall cost of heating.

An obvious limitation is that you need to live in a location served by a heat network in order to get your heating in this way, and at present they're not all that common.

They're also not as tightly regulated as other energy suppliers, which could result in consumer issues, such as being locked into long contracts. While cheap energy deals are hard to come by at the moment, those on heat networks could have difficulty switching to an alternative provider if better deals appear in the future.

These issues will need to be addressed if heat networks are to become a mainstream form of heating.

The government plans to identify areas that can be connected to a low carbon heat network over the coming years, with a view to starting transitions to heat networks in the 2030s and beyond.

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