If you can only fund one big-ticket retrofit measure this year, the question that comes up again and again is whether to put solar panels on the roof or replace the boiler with a heat pump. Both are the two most-searched, most-marketed retrofit measures in the UK right now, both attract grant support or export payments, and both get pitched by installers as “the one to do first.” The honest answer is that there isn’t a single correct order that applies to every home. It depends on your insulation, your roof, your electricity usage pattern, and how much cash you have to deploy in one go. This guide walks through the real UK cost and savings figures for both measures, explains the technical relationship between insulation, heat pumps and solar, and then sets out a decision framework so you can work out which applies to your property rather than following a rule of thumb that was written for someone else’s house.
What solar panels actually cost and save in the UK
According to Energy Saving Trust, an average home solar PV system costs around £6,100 to install. That typically buys a system of around 4.5 kilowatt-peak (kWp), using roughly 12 panels covering 20 to 30 square metres of roof. If you want to store the electricity you generate rather than exporting the surplus, battery storage is a separate cost on top, typically £5,000 to £8,000 depending on capacity.
On savings, Energy Saving Trust puts typical annual bill savings at around £360 a year for a home in Great Britain, plus further income of around £220 a year from selling surplus electricity back to the grid under the Smart Export Guarantee (SEG). Payback varies significantly by location because it depends on how much usable daylight your roof gets over a year: Energy Saving Trust’s figures show a system in London paying back in around 9 years, while the same system in Stirling takes 11 to 12 years. Carbon savings are around 750kg of CO2 a year for a typical GB household.
Those figures assume a fairly typical roof orientation and no major shading. A south-facing roof with no chimneys, trees or dormers overshadowing it will do noticeably better than these averages; a north-facing roof, or one broken up by rooflights and extensions, will do worse. It’s also worth being clear-eyed about what solar PV actually does: it generates electricity when the sun is up, which for most of the year in the UK does not line up neatly with when a household uses the most electricity. That timing mismatch is central to the question of whether solar pairs well with a heat pump, which we come back to below. If you want a proper design and quote for your roof, the Solar service page matches you with local MCS-certified installers who can survey your specific roof rather than relying on averages.
What a heat pump actually costs and saves in the UK
Air source heat pumps are the most common type installed in UK homes, and Energy Saving Trust puts the typical installed cost at around £11,000. That figure moves around a lot depending on the size of heat pump needed, whether your existing radiators need to be upgraded to work at lower flow temperatures, and whether you’re in a newbuild or an older property with more complex pipework and access.
The single biggest lever on the net cost is the Boiler Upgrade Scheme (BUS), a government grant covering England and Wales that currently pays £7,500 towards an air source or ground source heat pump. From 21 July 2026, that grant temporarily rises to £9,000 for eligible off-gas-grid properties in England and Wales, running through to March 2027. Your installer applies the grant on your behalf and deducts it from the quoted price upfront, so you never have to pay the full amount and claim it back. On an £11,000 install, a £7,500 grant brings the net cost down to roughly £3,500, and the temporary £9,000 rate for off-gas-grid homes would bring it closer to £2,000. Scotland has its own support through Home Energy Scotland loans and grants; Northern Ireland currently has no equivalent scheme.
On running costs, Energy Saving Trust is candid that the answer depends heavily on your electricity tariff. Heat pumps are more than three times as efficient as a gas or oil boiler in terms of the useful heat they produce per unit of energy input, but electricity costs more per kWh than gas in the UK, so on a standard variable electricity tariff a heat pump can end up costing slightly more to run than a modern gas or oil boiler. Move to one of the heat-pump-specific time-of-use tariffs now offered by several suppliers, however, and Energy Saving Trust notes running costs can drop below what a gas boiler would cost, particularly if you also disconnect your gas supply and stop paying its standing charge. Carbon savings are substantial regardless of tariff: around 2,300kg of CO2 a year for a typical GB household switching from a gas boiler.
The wide range in outcomes here is the important thing to take away. A heat pump’s running cost is not a fixed number the way solar’s generation roughly is; it depends heavily on your tariff, your radiators, and - as the next section covers - your insulation. For a proper heat loss survey and quote, the Heat Pumps service page connects you with local MCS-certified installers who will size a system to your actual property rather than a rule of thumb.
Why insulation changes the sizing and running cost of a heat pump
This is the piece of the puzzle that most cost comparisons leave out, and it’s the reason the “solar or heat pump first” question doesn’t have one universal answer. Before any MCS-certified installer can quote you for a heat pump, they need to carry out a heat loss calculation - a room-by-room assessment of how much heat escapes through your walls, floor, roof and windows at a typical winter design temperature. Energy Saving Trust’s installer guidance describes this heat loss calculation as “a key part” of sizing a heat pump correctly, because the whole point is to match the heat output of the pump to the actual heat loss of the building, not to over- or under-size it.
The average heat loss for a UK property sits somewhere around 6 to 8 kilowatts, but that figure moves substantially with insulation standard. A solid-walled Victorian terrace with no cavity or wall insulation, single glazing and an uninsulated loft will have a much higher heat loss than the same size house with cavity wall insulation, double glazing and 270mm of loft insulation - and that difference translates directly into needing a bigger, more expensive heat pump, run at a higher flow temperature, to keep the same rooms warm.
Flow temperature is the technical detail that matters most here. Heat pumps are dramatically more efficient at lower flow temperatures - the temperature of the water circulating through your radiators or underfloor heating. Industry efficiency data for a typical domestic heat pump shows a seasonal coefficient of performance (SCOP) of around 4.48 when running at a 35°C flow temperature, dropping to around 3.06 at a 55°C flow temperature - in other words, the low-flow-temperature setup delivers roughly 45% more heat per unit of electricity than the high-flow-temperature one. A well-insulated home loses heat more slowly, which means it can be kept warm with a lower flow temperature and smaller radiators (or the same radiators running cooler), directly improving the SCOP and cutting the electricity bill. A poorly insulated home often needs a higher flow temperature and larger, more expensive radiators to compensate, which pushes both the install cost and the running cost up.
This is also the technical basis for the widely cited “fabric first” principle in UK retrofit. PAS 2035, the government-recognised retrofit standard used across publicly funded energy efficiency schemes, defines its whole-house approach around “reducing heat demand by improving the building’s fabric before introducing new energy systems,” specifically to avoid installing heating systems sized for a leaky building and to avoid the damp and ventilation problems that can follow from tightening up a building without proper sequencing. In practice, this doesn’t mean every home needs a full insulation retrofit before a heat pump goes in - an already-insulated 2005-built semi doesn’t need much fabric work at all - but it does mean that if your property has cheap, high-impact insulation still to do (loft top-up, cavity wall fill, floor insulation), doing that first will shrink both the heat pump you need and what it costs to run. If your home is a period or solid-wall property where insulation is neither cheap nor straightforward, it’s worth reading our guide to insulating a period or Victorian home before you get quotes for a heat pump, since the insulation route you choose there affects the heat loss figure an installer will calculate.
Can solar panels actually power your heat pump?
The pitch is intuitive: put solar on the roof, run the heat pump off free daytime electricity, save on both bills at once. The reality is more mixed, and being honest about it matters because it’s the crux of the sequencing question for a lot of households.
The problem is timing. Solar panels in the UK generate the vast majority of their output between roughly April and September, and even in summer, generation is concentrated in the middle of the day. Heat pump demand is the opposite: it peaks in the coldest months, typically running hardest in the early morning and evening when a household wants the house warm and people are home, and barely at all in summer beyond hot water. In the depths of winter, when a heat pump is working hardest, daylight hours are short and solar output is at its lowest point in the year. That means in the exact months when a heat pump costs the most to run, solar contributes the least towards running it.
Where solar and a heat pump genuinely work well together is in the shoulder seasons (spring and autumn, when there’s meaningful heating demand and reasonable daylight) and for domestic hot water, which a heat pump typically heats on a cycle that can be shifted to run during the day when panels are generating. A battery makes this pairing considerably more useful, since it lets you store daytime solar generation and draw on it for the heat pump in the evening rather than losing that value to a low export payment. But a battery is an additional £5,000 to £8,000 on top of the panels, which changes the economics again.
The practical takeaway: solar PV can meaningfully offset a heat pump’s electricity use, but mostly outside the depths of winter, and more so with a battery than without one. If your primary aim is to bring down heat pump running costs specifically, a heat-pump-specific time-of-use electricity tariff is likely to move the needle more reliably across the whole year than solar generation will on its own - solar is best thought of as a complementary saving on top of that, particularly if you’re also home during the day and using electricity for other things.
So which should you do first? It depends on these four things
Given the above, here’s how to actually decide for your property, rather than following a generic rule.
- If your insulation is poor or unknown (pre-1980s solid wall or unfilled cavity, thin or absent loft insulation, single glazing): address the cheap, high-impact insulation measures first, or at minimum get a proper heat loss survey before committing to heat pump size and cost. Installing a heat pump sized around your current heat loss, then insulating afterwards, means you’ve paid for and are running a bigger system than you’ll ultimately need - the reverse order wastes money on both ends. Solar can go on at any point since it doesn’t depend on your heat loss.
- If your home is already well insulated (post-2000s build, or you’ve already done cavity, loft, and glazing upgrades): the fabric-first argument for delaying a heat pump doesn’t really apply to you - your heat loss calculation is likely to come back favourable, meaning a smaller, cheaper-to-run heat pump at a lower flow temperature. In this case there’s a reasonable case for doing the heat pump first, particularly to capture the £7,500 (or £9,000, if you’re off-gas-grid and eligible from July 2026) Boiler Upgrade Scheme grant before it changes again, and adding solar afterwards.
- If you use a lot of electricity during the day (you work from home, you’re retired, you run electric-heavy appliances or an EV during daylight hours): solar’s economics improve for you specifically, because you’re consuming more of what you generate rather than exporting it at the lower SEG rate. This tips the case towards solar first, or doing both together if budget allows, since your daytime usage pattern is exactly the profile solar performs best against.
- If budget is the binding constraint and you can only do one thing this year: the Boiler Upgrade Scheme grant has a real possibility of changing or closing in future spending reviews, in the way its predecessor schemes did, so there’s an argument for capturing it while it’s available if your insulation is already reasonable. Conversely, if your insulation clearly needs work, that’s the cheaper and lower-regret step to take first - a loft top-up or cavity fill costs a fraction of either a heat pump or solar array and reduces the cost of whichever comes next.
Notice that “solar or heat pump” is often the wrong framing entirely. For a lot of self-funded retrofits, the real first decision is whether insulation needs to happen before either measure, and the real second decision is which of solar or heat pump matches your usage pattern and grant timing better. Very few homes have a technical reason to rule either measure out; the question is sequencing and budget, not which one is objectively “better.”
A sensible phased approach if you can’t do everything at once
Most self-funded retrofits happen over several years rather than in one go, so here’s a practical order that reflects the research above rather than a marketing preference for one measure over another.
- Step one - cheap fabric measures. Loft top-up insulation and cavity wall fill (where you have a cavity) are the lowest-cost, fastest-payback measures available, at roughly £120 a year in savings for floor insulation alone according to Energy Saving Trust, and they directly reduce the heat pump size you’ll need later. Do these regardless of what comes next.
- Step two - get a heat loss survey, even if you’re not installing a heat pump yet. A proper MCS-standard survey tells you your actual heat loss figure and what flow temperature and heat pump size your home would need. This is useful information on its own, and most installers will do this as part of a no-obligation quote.
- Step three - decide between heat pump and solar based on the four factors above, factoring in that the Boiler Upgrade Scheme grant is a time-limited government scheme while solar’s economics are comparatively stable year to year (subject to your roof and location).
- Step four - the second measure, plus consider a battery if you did solar first and are now adding a heat pump, or consider a time-of-use heat pump tariff if you did the heat pump first and are now adding solar.
- Step five - solid wall insulation or other higher-cost fabric measures, if your property needs them and hasn’t had them yet. At roughly £12,000 for a whole solid-walled house according to Energy Saving Trust, with savings up to £330 a year, this is a bigger commitment that many homeowners phase in last, room by room, once the higher-impact heating and generation measures are in place.
None of this is a rigid formula - a homeowner with a well-insulated 1990s semi and a south-facing roof is in a genuinely different position from someone in an uninsulated Victorian terrace with a shaded north-facing roof, and the right order for each of them is different. What matters is going in with the real cost, savings and grant figures rather than assuming either measure is a universal “do this first,” and getting a proper survey before committing to either.
If you’re not sure where your own property sits on any of this - insulation standard, roof suitability, or what size heat pump you’d actually need - the fastest way to find out is to start with your home’s current EPC rating and get matched with a local specialist who can survey the specifics rather than work from averages.
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