Guide To Replacing A Boiler With A Heat Pump

Last updated: May 19, 2024

Heat pumps are a more eco-friendly and energy-efficient way to heat your home than traditional boilers. If you’re considering switching, here’s everything you need to know about replacing a boiler with a heat pump.

According to the Energy Savings Trust, replacing an old gas or LPG boiler with an air-source heat pump can save between £260 and £580 annually on energy bills in England, Scotland, or Wales.

Fossil fuel heating systems like gas or oil boilers will likely be phased out over time. Now might be the best time to switch to heat pumps to align with the UK government’s plan to reach net zero carbon emissions by 2050.

Switching from a boiler to an air-source heat pump will protect families from global oil and gas price uncertainties.

This guide explores everything you need to know about replacing a boiler with a heat pump, including the costs, pros and cons of heat pumps, and government incentives available to help with installation costs.

Replacing a boiler with a heat pump from Bosch
Image by Worcester Bosch

Key Takeaways:

  • Replacing your boiler with a heat pump is an excellent way to reduce your carbon footprint and the annual running costs of heating your home and water.
  • Installing an air source heat pump will cost between £14,000 and £19,000.
  • Installing a ground source heat pump can cost between £28,000 and £34,000.
  • Heat pumps are 300% efficient and produce three times more energy than they take in.
  • Grants available for heat pumps include the Boiler Upgrade Scheme, Home Energy Scotland, and the Nest Scheme.

Can A Heat Pump Replace My Boiler?

Yes! A heat pump can replace an LPG, natural gas, or oil boiler to heat water. The hot water can help heat your home through central heating systems, including underfloor heating and radiators.

Basically, anything a boiler can do, a heat pump can do more efficiently while producing fewer carbon emissions.

Replacing your boiler with a heat pump is an excellent way to reduce your carbon footprint and the annual running costs of heating your home and water.

Heat pumps are more sustainable, efficient, and environmentally friendly than boilers running on fossil fuels.

How Do Heat Pumps Work?

Heat pumps transfer heat from the outside environment into your property using a four-step process. The four-step process is called a refrigeration cycle and includes:

Evaporation

The heat pump takes in heat from the air, ground, or sometimes, water, and transfers it to a heat exchanger containing a refrigerant.

The refrigerant absorbs the heat and evaporates, turning it into a low-temperature, low-pressure gas.

Compression

The gas then moves to an electrically powered compressor that compresses the refrigerant.

The compression increases the gas’s pressure, raising the gas temperature.

Condensation

The hot gas moves to the heat exchanger where it’s circulated. It then transfers its heat to a cold water circuit, causing the water to heat up as it absorbs heat from the gas.

Once the water reaches the desired temperature, it’s sent to your home’s underfloor heating or radiators to warm your home.

After transferring the heat to the water circuit, the refrigerant cools down enough to turn back to liquid.

Expansion

The cooled refrigerant then moves through an expansion valve, lowering the pressure and allowing it to absorb more heat energy.

The refrigerant then returns to the heat exchanger to repeat the cycle.

The diagram below illustrates the process:

Source: Energy Savings Trust

Can A Heat Pump Work With A Boiler?

Yes. Heat pumps can work with boilers to create hybrid systems. Many boiler manufacturers now offer hybrid systems with heat pumps to facilitate the move to low-carbon heating solutions.

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The hybrid system uses a standard heat pump and a gas, LPG, or oil boiler. The boiler can be an existing one or a new one can be installed simultaneously with the heat pump.

A hybrid system can be suitable if you’re looking for lower-carbon heating, but a standard heat pump isn’t suitable.

A hybrid system can be ideal for you if:

  • Your household has a high heat demand – Your home’s heat demand refers to the heat needed to provide hot water and heating. A single heat pump may not be enough to meet your needs, especially if you live in a large home where insulation is impractical or too expensive.
  • The heat pump may not lower your energy bills – Sometimes modern, A-rated gas boilers can deliver heat cheaper than heat pumps, especially when fuel prices are low. Hybrid systems feature controls that automate when and how the heat pump operates based on fuel costs, electricity costs, time of day, and whether you have solar panels.

Ensure you understand the running costs of your heating system to determine a suitable design and configuration for a hybrid system.

The Energy Savings Trust recommends getting at least three quotes from different installers, with recommendations on the most suitable system for your property and needs.

What Are The Differences Between Heat Pumps and Gas Boilers?

One key difference between heat pumps and gas boilers is that heat pumps have cooling capabilities, while boilers don’t.

The table below shows other crucial differences between heat pumps and gas boilers:

FeatureHeat pumpsGas boilers
EfficiencyMore efficientLess efficient
FuelUse electricity to transfer the outside heat to the insideBurns natural gas to produce heat
SpaceRequires space for an outdoor unitMight require extra indoor space for hot water cylinders and tanks (for system and conventional boilers)
Environmental impactMore environmentally friendlyProduces carbon emissions
VersatilityCan heat and cool your homeCan only heat your home
LongevityUp to 25 yearsUp to 15 years

What Are The Advantages of Heat Pumps Over Gas Boilers?

Heat pumps are generally more eco-friendly and efficient and offer a versatile way to heat and cool your home.

Replacing an old boiler with a heat pump is worth considering due to its advantages. These include:

Environmental Impact

Heat pumps are a more eco-friendly way to heat your home than gas boilers.

They produce little to no more carbon emissions, helping to reduce your carbon footprint, especially when you combine them with renewable energy sources like solar panels.

Efficiency

Heat pumps are more energy-efficient than gas boilers, allowing them to produce more heat using less energy.

This provides you with significant savings on your energy bills.

Longevity

Heat pumps have a longer lifespan than gas boilers, and with good maintenance, they can last up to 25 or 30 years. Most boilers last between 10 and 15 years.

Versatility

Heat pumps can provide heating and cooling for your home, making them a one-stop solution for all your climate control needs.

Enhanced Comfort

Heat pumps provide evenly distributed and more consistent heat than gas boilers. They can significantly improve your home’s overall comfort.

Check out our boiler brand price guides and comparisons:

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Want to learn how to use your boiler better? Read our complete guide on boiler flow temperature, how to optimise your boiler settings, and find out how much gas a boiler uses here.

How Much Does A Heat Pump Cost?

The cost of installing a heat pump will depend on the kind of heat pump you want.

The Energy Savings Trust notes that ground source heat pumps cost between £28,000 and £34,000, depending on how the pipes are installed.

Installing an air source heat pump will cost between £14,000 and £19,000.

The cost of installing the heat will depend on various factors, including:

  • Whether your property is a new build or an existing house. For an established property, you may need to replace all the radiators and rebuild many of the pipes.
  • Your property’s size.
  • The work needed to adapt your existing heating system for a heat pump.

If you have a digger and can excavate the horizontal trenches yourself, you might just save money on installation.

Wondering how much a new boiler costs? Check out our guide on options available if you need a new boiler but can’t afford it, as well as boilers on finance and government boiler grants here.

Do Heat Pumps Heat As Well As Gas Boilers?

Heat pumps can give a higher efficiency rate than boilers.

They generally produce three times more energy than they take in, making them around 300% efficient.

Heat pumps are more efficient than gas boilers because they harvest heat from the environment instead of an energy source like natural gas.

The amount of heat produced for every unit of electricity the heat pump uses is called the Coefficient of Performance (CoP). If a heat pump has a CoP of 3.0, it will give out three units of heat for every unit of electricity it uses. 

In contrast, an A-rated gas boiler with an efficiency of 85% will only produce 0.85 units of heat for every unit of gas it uses.

Heat pumps usually have a published datasheet showing the measured CoP under specific test conditions.

However, installers must also calculate the seasonal performance factor (SPF) or the seasonal coefficient of performance due to the external temperature variations heat pumps experience throughout the year.

The installer will calculate the SPF based on the system design for your home. It will show how the heat pump should perform based on the size of your radiators and the average temperature at your location.

Given the constant advancement of heat pump technology, their performance rate will only enhance in the future, setting greater efficiency criteria that will be difficult to match with other heating devices on the market.

Who offers the best boilers deals in the UK? Check out our review of online boiler installation companies, boiler brands, and the best UK boilers that have topped our list concerning new boilers in the current year.

We also covered the boiler brands to avoid and the most reliable boilers currently available.

Is My Home Suitable For A Heat Pump?

Heat pumps are suitable for all kinds of homes. The kind of heat pump that best suits your home will depend on your budget and how much space you have.

The two types of heat pumps common in the UK include:

Air Source Heat Pumps

Air source heat pumps (ASHPs) are the UK’s most common type of domestic heat pump. They’re relatively small, and the unit is around the size of two wheelie bins side by side.

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An ASHP is also cheaper to install than other types of heat pumps and can be a monobloc or split system.

Monobloc systems have all the components in a single outdoor unit, with pipes carrying water to the central heating system and a hot water cylinder inside your home.

Split systems separate the components between indoor and outdoor units.

Monobloc systems are usually cheaper and quicker to install and don’t take up much space inside your home. However, they’re generally slightly less efficient than split systems.

Split systems can be more efficient because some heat transfer occurs inside the building where it’s warmer, resulting in less heat loss.

Ground Source Heat Pumps

Ground source heat pumps (GSHPs) transfer heat from the ground outside your home to heat your radiators or underfloor heating. They can also heat water stored in a hot water cylinder.

GSHPs are suitable if you have a large outdoor space or garden where you can sink boreholes or run a loop of underground pipes.

GSHPs are usually more efficient than ASHPs but are more expensive to install.

How old is your boiler? Should you consider repairing the boiler or looking at the latest boiler prices? It’s no secret that boiler efficiency deteriorates over time.

What Grants Are Available For Heat Pumps?

Depending on where you live, several options exist to help you reduce the costs of replacing a boiler with a heat pump. These include:

The Boiler Upgrade Scheme (BUS)

BUS is a UK government grant that allows eligible homeowners in England and Wales to receive funding to install heat pumps or biomass boilers.

Since October 2023, the level of funding increased from £5,000 to £7,500 to assist with the cost and installation of heat pumps.

If you applied for BUS before 2023 and the heat pump has yet to be installed, you can ask the installer to cancel the initial grant and reapply for the increased amount.

Home Energy Scotland

Home Energy Scotland offers grant funding, interest-free loans, or a combination to help homeowners and self-builders install renewable systems like heat pumps.

You can apply for up to £7,500 to install a new heat pump, rising to £9,000 if you live in a rural or island home.

A heat pump may cost more than the grant amount. As such, you can apply for an optional interest-free loan to cover the remainder.

The Nest Scheme

The Nest scheme offers advice and free home energy efficiency improvements, including heat pump installations. You must meet certain conditions to be eligible for funded home improvements. These include:

  • A home with an asset rating of 54 (EPC E) or less or an asset rating of 68 (EPC D) where you or a household member has a chronic circulatory, respiratory, or mental health condition
  • Owning or privately renting your home
  • Living in a low-income household or claiming a means-tested benefit like Child Tax Credit, Council Tax Reduction, Housing Benefit, or Pension Credit

You’ll need to provide evidence that you meet the eligibility criteria.

Such evidence can include prescriptions or treatment plans showing your health condition, a blue badge, or a discretionary pass demonstrating your eligibility for the additional income thresholds.

Replacing A Boiler With A Heat Pump Conclusion

Heat pumps are generally more cost-effective and energy-efficient than gas boilers in the long run. If you have an old gas boiler, replacing it with a heat pump can improve your home’s energy efficiency, save you money and reduce your carbon footprint.

Although the initial costs can be high, the heat pump will gradually pay for itself, and you can start enjoying the benefits of lower running costs for 25 to 30 years. Best of all, you can access various grants to help with the upfront costs of replacing a boiler with a heat pump.

Sources and References

  • https://energysavingtrust.org.uk/advice/air-source-heat-pumps/?_gl=1124a7ro_upMQ.._gaMjY5NDY5Nzk3LjE3MTYxMTI3MTE._ga_GPYNXFLD7G*MTcxNjExMjcxMC4xLjAuMTcxNjExMjcxMC4wLjAuMA.
  • https://energysavingtrust.org.uk/advice/hybrid-heat-pumps/#:~:text=A%20hybrid%20heat%20pump%20refers,time%20as%20the%20heat%20pump.
  • https://www.homeenergyscotland.org/home-energy-scotland-grant-loan
  • https://www.gov.wales/get-free-home-energy-efficiency-improvements-nest/eligibility