Seven Quotes, One Loft: The Real Payback Maths Behind a 2026 Heat Pump Grant

A heat pump quote can feel a bit like a lottery ticket. One installer says £9,000, another says £14,000, and a third mentions a grant that supposedly makes it all vanish. The Boiler Upgrade Scheme is genuinely useful, but it is not a magic discount that turns every old gas boiler into a money-saving upgrade. If you are weighing up a heat pump in 2026, the sensible job is not to chase the biggest grant headline. It is to work out what you will actually pay, what you will actually save, and how long the gap takes to close.

What the grant does — and does not — cover

In England and Wales, the Boiler Upgrade Scheme offers a headline grant of £7,500 towards an air-source heat pump, with a lower amount for ground-source systems. Scotland runs its own grant and loan arrangements, so do not assume the same rules apply north of the border.

The key detail is that the grant is usually taken off the installer's invoice. You are not handed a cheque to spend on radiators, pipework or a new consumer unit. The installer has to be MCS-certified, and the property and system need to meet the scheme rules. That means the grant reduces the quoted price of an eligible installation — it does not cover every extra that a real house tends to need.

This is where the first gap opens up. A quote might say '£12,000 before grant'. The grant brings it to £4,500. But if your quote also includes radiator upgrades, extra pipework, a new hot water cylinder or electrical work, those costs can sit outside the simple headline comparison. Always ask for a line-by-line breakdown: heat pump unit, cylinder, labour, radiators, pipework, electrical work, commissioning, grant admin and any make-good work.

The insulation prerequisite nobody quotes first

Heat pumps run at lower flow temperatures than gas boilers. That is fine in a well-insulated home with suitably sized radiators. It is less fine in a draughty Victorian terrace with loft insulation that has been flattened by storage boxes.

Before comparing heat pump quotes, do the boring fabric checks. Loft insulation depth, cavity wall insulation, draught-proofing, suspended floors and glazing all affect how much heat the system needs to deliver. A good installer will carry out a room-by-room heat loss calculation rather than simply matching the size of your old boiler. If they do not, ask why.

Some quotes will include insulation upgrades; others will assume you will sort them separately. That can make a cheap quote look cheaper than it really is. It can also mean the heat pump ends up working harder than expected, which is bad for running costs and bad for payback.

Why two quotes can differ by thousands

Installer quotes vary for reasons that are not always sinister. One firm may have a bigger overhead base. Another may be busy and pricing accordingly. One may assume standard radiator replacements; another may plan for larger radiators in every room. Pipework routes, cylinder location, electrical capacity, scaffolding, listed-building consents and even parking can move the number.

There is also the grant paperwork. Some installers handle it smoothly; others build in an admin buffer. None of this means the cheapest quote is wrong, but it does mean you should compare the scope, not just the bottom line. Ask each installer what happens if the heat loss survey reveals more work. Is the quote fixed, or is it an estimate with a likely top-up?

A useful sanity check is to ask for the proposed radiator sizes and the expected flow temperature. If the design relies on a high flow temperature to keep the house warm, the running-cost case may be weaker. If it plans for larger radiators and a lower flow temperature, the upfront quote may be higher but the day-to-day numbers may be better.

Running costs: the assumption that decides everything

Payback is not decided by the grant alone. It is decided by the difference between what you would have spent on gas and what you will spend on electricity.

As a rough illustration, suppose gas costs around 6.5p per kWh and an old gas boiler is about 90% efficient. That puts the cost of delivered heat at roughly 7.2p per kWh. If electricity costs around 24p per kWh and the heat pump achieves a seasonal COP of 3.2, the cost of delivered heat is about 7.5p per kWh. In that example, the heat pump is broadly level with gas — not a huge saving, not a disaster.

Change the assumptions and the picture moves. A well-insulated home with a seasonal COP of 3.8 does better. A poorly insulated home with a lower COP does worse. A time-of-use heat pump tariff can help if you can shift demand, but it only works if your hot water and heating patterns fit the cheap windows. Standing charges, hot water demand and the amount of heat you actually use all matter too.

Do not accept a salesperson's 'heat pumps are cheaper to run' line without your own arithmetic. Take your annual gas usage in kWh, apply a realistic efficiency figure, then compare it with your expected electricity use under a heat pump tariff. If the numbers are close, the payback will depend heavily on the upfront premium.

The break-even sheet

A simple payback calculation looks like this: extra upfront cost after grant, divided by annual running-cost saving. If there is no saving, there is no payback — just a more expensive way to heat the house.

Take a made-up but plausible example. A replacement gas boiler might cost £3,000. A heat pump installation might be £12,000 before the £7,500 grant, so £4,500 after grant. The upfront premium is £1,500. If the heat pump saves £150 a year on running costs, payback is ten years. If it costs £100 a year more to run, the premium never pays back on running costs alone.

That does not automatically make it a bad decision. Comfort, carbon, noise, summer cooling potential and the avoidance of a future boiler replacement all have value. But if you are doing this purely as a household budgeting exercise, be honest about which column the numbers land in.

Hidden extras that stretch the payback

Watch for radiator upsizing, pipework alterations, a new cylinder, electrical consumer-unit upgrades, planning or listed-building consent, and the cost of removing old tanks or pipework. Annual servicing may be £150 to £250. Some warranties depend on it. Home insurance may need a quick check if the system includes external units or a new cylinder.

Also budget for the paperwork. The grant may be deducted from the invoice, but you still need to confirm the installer is registered and that the quote clearly separates eligible and ineligible costs. A stretched payback often starts with a quote that looked simple at the top and got complicated at the bottom.

A sensible shopping sequence

Start with insulation and draught-proofing. Then get a heat loss survey, not just a boiler-size guess. Get at least three itemised quotes from MCS-certified installers. Ask each one to model running costs using your actual tariff, not a generic assumption. Check the grant rules for your nation and property. Then decide whether the upfront premium is worth it to you.

The heat pump grant is a real help, but it is not a lottery win. The homeowners who do best are the ones who treat it as one line in a household budget — and run the payback maths before the salesman runs theirs.