The boiler versus heat pump decision is almost never made in calm conditions. A boiler failure creates immediate pressure to decide, and the financial comparison needs to be made quickly with incomplete information. This calculator is built for that moment. It takes the cost of a boiler replacement, the cost of a heat pump net of any Boiler Upgrade Scheme grant, your current annual heating bill, and your property’s insulation level, and runs a year-by-year cost comparison over up to twenty years showing which option costs less in total at each point.
Three energy price scenarios are available: a conservative scenario where gas and electricity prices move broadly in line with inflation, a central scenario where gas becomes relatively more expensive as the grid decarbonises, and an optimistic scenario where the transition accelerates more rapidly. No one knows which will materialise, and the scenarios should be read as a range of possibilities rather than forecasts. The crossover year, the point at which the heat pump becomes cheaper in total than the boiler replacement, is the most useful output. All figures are illustrative. Squared Money is an introducer, not a lender.
At a Glance
- For gas-heated homes, the heat pump is typically more expensive in total for the first five to ten years even with the BUS grant. The crossover point depends primarily on how energy prices move and how well-insulated the property is. The calculator shows it honestly for your figures: the cost comparison calculator.
- For oil and LPG-heated homes, the crossover typically comes sooner. The narrower gap between electricity and oil or LPG prices means the running cost saving is more immediate, and the heat pump often becomes cheaper in total within five to eight years even without significant energy price movement: the cost comparison calculator.
- The Boiler Upgrade Scheme changes the capital comparison significantly. Without the £7,500 grant, the heat pump capital cost is typically £7,500 to £12,500 more than a boiler replacement. With the grant, that gap narrows to £0 to £5,000 for a mid-range installation. Toggle the grant on and off to see how much it matters for your figures: the cost comparison calculator.
- The regulatory direction of travel is away from gas boilers. New gas boiler installations in new-build properties in England are already restricted. The government has stated an intention to phase out the installation of new gas boilers in existing properties, though the timeline has been subject to revision. A gas boiler installed today may need to be replaced again before 2040: the regulatory direction.
- Insulation quality is the most controllable variable in the heat pump’s financial case. A better-insulated property achieves a higher SCOP, which reduces running costs and brings the crossover year forward. Improving insulation before switching, if time allows, improves every figure in this comparison.
Boiler vs heat pump: year-by-year cost comparison
Compare the total cost of replacing your boiler against installing a heat pump over your chosen timeframe. All figures are illustrative and depend on actual energy prices, installation costs, and property conditions.
Your current heating
Replacement costs
Energy price scenario
Energy price forecasts are speculative. These scenarios represent a range of possible outcomes, not predictions. The actual outcome will depend on global energy markets, government policy, and the pace of grid decarbonisation.
| Year | Boiler annual cost | Heat pump annual cost | Boiler cumulative | HP cumulative | HP vs Boiler |
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About This Calculator
What is included in the comparison
Capital cost, running cost, and maintenance
The cumulative cost for each option includes: the capital cost of installation in year zero, annual running costs (fuel or electricity for the heating system) adjusted each year for the energy price scenario selected, and annual maintenance costs. Boiler maintenance is set at your chosen annual service figure. Heat pump maintenance is set at 85% of that figure, reflecting the generally lower service frequency needed for heat pumps. Neither column includes radiator upgrades, which may be needed for some heat pump installations and should be included in the heat pump capital cost.
What is not included
Loan costs, radiator upgrades, hot water cylinder
This comparison shows the total cost before loan interest. If the heat pump installation is financed by loan, add the total interest cost to the heat pump capital figure to see the financed comparison. The heat pump running cost calculator includes a loan section for this purpose. Radiator upgrade costs, which apply to some properties, and the hot water cylinder cost, which is usually included in the installer quote, should both be verified when obtaining a quote.
The energy price scenarios
What each scenario assumes and why it matters
The Conservative scenario assumes gas and electricity prices rise in line with general inflation: no relative change between the two. The Central scenario reflects a gradual decarbonisation of the electricity grid, making electricity relatively cheaper over time. The Optimistic scenario reflects a faster transition. All three are speculative. The BEIS long-term energy price projections broadly support the Central scenario as a central estimate, but energy price forecasting over fifteen years is inherently uncertain. Running all three scenarios gives a range rather than a single answer.
The crossover year
What it means and what it does not
The crossover year is the first year in which the cumulative total cost of the heat pump falls below the cumulative total cost of the boiler replacement. Before that year, the boiler replacement has cost less in total. After it, the heat pump has. The crossover year only matters if you plan to remain in the property and retain the heat pump until that point. If you are likely to move or make another change before the crossover year, the boiler replacement is the lower-cost option on your timeframe, regardless of what the table shows beyond that point.
The Regulatory Direction
A gas boiler installed today is unlikely to be the last heating system in a property that remains occupied for the next twenty years. The UK government has committed to net zero by 2050, and the decarbonisation of home heating is a central part of that commitment. New gas boiler installations in new-build properties are already restricted, and the government has stated an intention to phase out the installation of new gas boilers in existing properties, with the most recent position pointing toward 2035 as the target date for the phase-out of new gas boiler installations. This date has been revised several times and should not be treated as fixed policy, but the direction of travel is clear.
The practical implication is that a gas boiler installed today to replace a failed unit may itself need to be replaced before 2040, either because it reaches end of life or because regulations change. If that second replacement is also a gas boiler, the cost appears in any comparison beyond fifteen years. If it is a heat pump, the heat pump capital cost moves forward and the running cost advantage starts earlier. Neither the fifteen-year comparison in this calculator nor any consumer-facing tool can model this with certainty: the regulatory timeline is too uncertain. What the comparison does show is that the heat pump eliminates this uncertainty by being a longer-lived technology with a longer expected regulatory future. This has value that does not appear in a pure cost comparison and is worth considering alongside the financial figures.
If your boiler has broken down today: the Boiler Upgrade Scheme requires an MCS-certified installer and a valid EPC before the grant can be claimed. The application process takes time that a broken heating system may not allow. Some households in a boiler failure situation have installed a replacement boiler on an emergency basis and then applied for the BUS to fund a heat pump at a planned later date. This is a legitimate approach: the BUS grant is for new heat pump installations, not for removing an existing boiler, so a recently installed replacement boiler does not disqualify a subsequent heat pump application. Check the current BUS terms on GOV.UK before relying on this.
How to Use This Calculator
Enter your current system details
Select your current fuel type and enter your annual heating bill. For gas, use the gas portion of your energy bill only, not the full dual-fuel bill. Your EPC rating determines the heat pump’s estimated SCOP: find your current EPC at the government’s Find an Energy Certificate service if you do not have a paper copy.
Set the replacement costs
Enter the boiler replacement quote you have received, or use £2,500 as a typical mid-range figure for a standard combi replacement. For the heat pump, enter the installed cost from an MCS-certified installer quote, or use £10,000 as a mid-range starting point. Toggle the BUS grant on or off based on whether you believe you qualify: the heat pump must be installed by an MCS-certified installer and the property must have a valid EPC with no outstanding insulation recommendations.
Choose your comparison horizon and scenario
Select how many years you want to compare. If you plan to sell within ten years, use ten. If you are planning for the long term, use fifteen or twenty. Then select an energy price scenario. Run all three to see the range: the Conservative scenario shows the position if prices move broadly with inflation. The Central scenario reflects the government’s central projection for the energy transition. The Optimistic scenario shows what happens if gas becomes significantly more expensive.
Read the crossover year and total position
The starred row in the table is the crossover year. Before that row, the boiler replacement has cost less in total. After it, the heat pump has. The summary cards at the top show the crossover year and the total position at your chosen horizon at a glance. The crossover year is the most practically useful output for decision-making.
Related Tools and Guides
Tool
Heat pump running cost calculator
Compares estimated annual heat pump running costs against your current system including the loan section. Use this for a detailed annual cost view and to model the loan interest impact on the overall position.
Tool
Energy efficiency loan payback calculator
Models when cumulative energy savings overtake total loan interest for any energy efficiency improvement. Use this to add loan interest to the heat pump side of the comparison if you are financing the installation.
Guide
Government grants vs home improvement loans
Covers the Boiler Upgrade Scheme eligibility requirements in full, including the EPC and insulation conditions, how the grant is claimed, and what funding is currently available.
Guide
Home improvement loans for energy efficiency upgrades
Covers all main energy efficiency improvements including heat pumps, with cost ranges, saving profiles, and loan type guidance. Includes the case for insulation before a heat pump installation.
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Checking won’t harm your credit scoreFrequently Asked Questions
My boiler has just broken down. How do I get a heat pump installed quickly enough?
The honest answer is that in most boiler failure situations, a heat pump cannot be installed quickly enough to avoid a period without heating. A heat pump installation requires an MCS-certified installer, a heat loss calculation, a BUS grant application if applicable, potentially radiator or pipework upgrades, and usually a new hot water cylinder. The end-to-end process typically takes four to twelve weeks from initial contact to installation. A replacement boiler can usually be installed within a few days.
The most practical approach in a boiler failure is to separate the emergency from the longer-term decision. Install a replacement boiler if the property needs heat immediately. This does not preclude a heat pump installation at a later planned date: the BUS grant applies to new heat pump installations and is not affected by the presence of a recently installed gas boiler. Once the immediate heating crisis is resolved, you can take the time to get proper heat pump quotes, improve insulation if needed, confirm BUS eligibility, and plan the installation at a time that is not driven by an emergency. The financial comparison in this calculator applies equally whether you are making the decision now or in twelve months.
Does the comparison change if I need to upgrade radiators for the heat pump?
Yes, significantly. Radiator upgrades add to the heat pump capital cost and push the crossover year further out. The extent of the upgrade needed depends on the size of your existing radiators and the flow temperature the heat pump needs to operate at. In a well-insulated property where the heat pump can run at low flow temperatures of 40 to 50 degrees Celsius, many standard-sized radiators will perform adequately and no upgrade is needed. In a less well-insulated property requiring higher flow temperatures, some or all radiators may need replacing with larger units. An MCS-certified installer will identify which radiators need upgrading as part of the heat loss calculation, and the cost should be included in the installation quote.
To include radiator upgrade costs in this comparison, add them to the heat pump installed cost slider. If your installer quote includes radiator upgrades as a separate line item at £2,000, set the heat pump cost slider to the panel installation cost plus the £2,000. The comparison will then reflect the full cost of switching to the heat pump including all works needed to make it perform correctly. Treating the radiator upgrade as a separate decision after the heat pump is installed is a common planning error that underestimates the heat pump’s true capital cost.
What happens to the comparison if I move house before the crossover year?
If you sell the property before the crossover year, the heat pump has cost more in total than the boiler replacement up to that point, based on the figures in this calculator. The sale may or may not recover some of that additional cost through a higher sale price: a property with a heat pump and a higher EPC rating may attract a modest premium in the current market, though the evidence for this is still developing. Any premium achieved at sale should be weighed against the additional upfront cost of the heat pump when assessing the overall financial position on a short horizon.
One consideration that does not appear in this calculator is the buyer’s perspective. A property with a modern heat pump installation and a good EPC rating is progressively easier to sell to buyers who are aware of upcoming regulatory changes and running cost expectations. Conversely, a property with an aging gas boiler in the context of expected future regulation changes may face greater scrutiny. This is speculative and property-specific, but it is worth considering as an additional factor in the decision for anyone who expects to sell within ten years.
Is a ground source heat pump ever worth considering over an air source?
Ground source heat pumps extract heat from the ground rather than from the air and achieve higher SCOPs, typically 3.5 to 4.5, because ground temperatures are more stable than air temperatures in winter. This makes them more efficient at exactly the time of year when a heat pump is working hardest. The financial case for a ground source heat pump is therefore better than for an air source unit in terms of running costs. However, ground source installation requires either a borehole (drilled to 80 to 150 metres) or horizontal ground loops (requiring significant garden area), and the installation cost is typically £20,000 to £35,000, substantially higher than an air source installation.
The BUS grant of £7,500 applies to ground source heat pumps as well as air source, which reduces the net cost but does not close the gap between the two technologies. Ground source is worth considering for properties with suitable land, particularly those on oil or LPG heating where the running cost saving is already strong for air source, and where the additional efficiency improvement from ground source produces a faster crossover year that justifies the higher capital cost. For most urban and suburban properties without significant garden space, air source is the practical choice.
Squaring Up
The boiler versus heat pump decision is genuinely context-dependent, and the right answer varies significantly by fuel type, property, and how long you plan to stay. For oil and LPG properties, the running cost saving is usually real and the crossover year often falls within ten years even on conservative energy price assumptions. For gas properties, the crossover depends heavily on energy price movement: on the conservative scenario it may be beyond the comparison horizon, on the central or optimistic scenarios it comes into view. The three scenarios in this calculator give you a range rather than a false single answer.
What the calculator cannot fully capture is the regulatory direction. A gas boiler installed today is likely to need replacing again before the end of its potential twenty-year life, and that second replacement may be into a market where gas boilers are more restricted or more expensive. That uncertainty has value that does not appear in a cost table, and it is the strongest non-financial argument for choosing the heat pump now when the BUS grant is available to reduce the capital cost difference.
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Checking won’t harm your credit score Check eligibilityThis tool is for illustrative purposes only and does not constitute financial, energy, or legal advice. All running cost estimates, energy price scenarios, and SCOP values are illustrative and will differ from actual outcomes, which depend on your specific installation, property, usage, and tariff. Energy price scenarios are speculative and do not represent forecasts. The Boiler Upgrade Scheme eligibility conditions and funding availability are subject to change: verify current status on GOV.UK before making any decisions based on the grant. Regulatory statements regarding the future of gas boiler installations reflect government policy as understood at the time of writing and are subject to revision. Your home may be at risk if you do not keep up repayments on a secured loan.
