Solar Panels vs Heat Pump: Which Should You Install First?
This is one of the most common questions people ask when they start decarbonising a home, and the honest answer is not the one most comparison pages give. It isn't about which has the better return. The returns are closer than you'd think, and both are slow.
Short answer: the age of your boiler decides this, not the ROI. If your boiler is near the end of its life, do the heat pump first, because you were about to spend two and a half grand on heating kit anyway and that changes the sum completely. If your boiler has years left, do solar first. If you can afford both, do both.
The Numbers
| Feature | Solar Panels | Heat Pump |
|---|---|---|
| Upfront cost | Around £7,600 for a typical 4.5 kWp system | £9,000–£13,000 (around £12,000 typical) |
| Grant available | None (but 0% VAT until March 2027) | £7,500 BUS grant |
| Net cost after grant | Around £7,600 | £1,500–£5,500 |
| Annual benefit | Roughly £630–£840, bills plus export payments | £0–£170 vs a modern gas boiler, around £275 if you also drop the gas standing charge. Far more vs oil, LPG or electric |
| Payback period | 9 years (London) to 12 years (Stirling) | Under 5 years if you were replacing a boiler anyway, 20+ years if you weren't |
| Disruption to install | 1–2 days, minimal | 2–5 days, potentially significant |
| Maintenance | Very low, but budget for an inverter at around year 12 | Annual service |
| Lifespan | 25+ years, inverter replaced at around 12 | 20 to 25 years |
Solar figures are from the Energy Saving Trust, which puts a typical 4.5 kWp system at around £7,600 and payback with export payments at 9 years in London, 9–10 in Aberystwyth, 10–11 in Manchester and 11–12 in Stirling. Divide the cost by the payback and you get the annual benefit: roughly £840 a year in the south, £630 in central Scotland. Anyone quoting you £1,500 a year from a domestic roof is either selling you something or has counted the same kilowatt-hour twice. The heat pump figure is from the same source: "The typical cost of installing an air source heat pump is around £12,000".
Solar's Return Is Good, Not Spectacular
Solar is the more predictable of the two. Panels have no moving parts, they need almost nothing from you, and the saving arrives every year whether or not you change how you live. Nine to twelve years to pay back on a 25-year asset is a genuinely decent home improvement.
The one cost people forget is the inverter. The Energy Saving Trust reckons on replacing it at around 12 years, and that's a real few hundred pounds landing right about the time the system finishes paying for itself. It doesn't wreck the case, but leave it out and your spreadsheet is lying to you.
The savings come from two places: electricity you don't buy, and Smart Export Guarantee payments for what you send back. How the split falls depends entirely on when you're home. Someone in all day on a south-facing roof self-consumes a lot and does well. Someone out from eight till six exports most of it at 12p and buys it back at 26.32p, which is why batteries and time-of-use tariffs keep coming up in the same conversation.
The Heat Pump Sum Has Just Flipped
For most of 2026 a heat pump cost slightly more to run than the gas boiler it replaced. That reversed with the October price cap: gas went up 8.7% while electricity rose 0.8% and lost its VAT until March 2027. Here's the current arithmetic for a 3-bed semi needing 12,500 kWh of heat a year.
| Gas boiler at 90% | Heat pump at SCOP 3.0 | Heat pump at SCOP 3.5 | |
|---|---|---|---|
| Energy needed | 13,889 kWh gas | 4,167 kWh electricity | 3,571 kWh electricity |
| Unit rate | 7.97p | 26.32p | 26.32p |
| Annual cost | £1,107 | £1,097 | £940 |
| Difference | n/a | £10 cheaper | £167 cheaper |
The break-even point against a 90% gas boiler is a SCOP of 2.97. Anything above that and the heat pump is cheaper to run. Anything below and it isn't, which is why the quality of the install matters more than the badge on the box. Get the gas meter removed entirely and you save the 29.68p a day standing charge on top, another £108 a year.
But look at that saving next to the cost. Even at £3,500 net after the £7,500 grant, £167 a year is a twenty-year payback, which is the whole life of the machine. As a standalone investment a heat pump doesn't compete with solar, and we're not going to pretend otherwise.
Which Is Why Your Boiler Decides It
The heat pump sum changes completely the moment your boiler is on its last legs, because the money you should be comparing isn't the full price. It's the difference between the heat pump and the boiler you were about to buy anyway.
A new combi runs about £2,750 fitted. A heat pump at £11,000 installed, the middle of the £9,000 to £13,000 range, is £3,500 after the BUS grant. The genuine extra cost of going heat pump instead of boiler is therefore around £750, and at £167 a year that pays back in under five years, on a system that lasts 20 to 25 years, about as long as two boilers.
Do it the other way round, replace a perfectly good boiler with a heat pump for no reason, and you're spending £3,500 to save £167. That's the whole argument on this page, in two paragraphs.
So: if your boiler is 12 years old or more, start getting heat pump quotes now. These installs take planning. You may need a couple of radiators upgraded, a new cylinder, and a proper room-by-room heat loss calculation, and none of that happens in the week your boiler dies in February. The worst possible outcome is an emergency gas boiler swap that locks you in for another 15 years.
Boiler Fine? Do Solar
If your boiler was fitted in the last few years, solar is the better first move. It pays back faster, it doesn't care what heating you have, and it makes the heat pump cheaper to run when you do get round to it. There is no downside to the order.
Spend the money on panels and, if you're out during the day, seriously price up a battery at the same time. Doing both at once is cheaper than adding storage later because you're only paying for scaffolding, an electrician and a DNO application once.
The Combination Is Still the Best Answer
A heat pump running partly on your own solar is the cheapest way to heat a UK home short of moving somewhere warmer. In spring and autumn a decent array covers a fair chunk of the daytime heating load outright.
Be realistic about the limits, though. Heat demand peaks in December and January, which is exactly when a UK roof generates least. Solar will not power your heat pump through a cold snap, and anyone who tells you it will is selling. What it does do is knock a meaningful slice off the shoulder months and most of your hot water from March to October.
If budget allows, install both together. You'll often get a better price from an installer doing both, and the systems can be commissioned to work together from day one rather than bolted together later.
What If You Have Oil Heating?
If you're on oil, stop reading this comparison and go straight to the heat pump. Kerosene at 113.52p a litre works out around 10.97p per kWh, and an 85% oil boiler turns that into 12.9p per kWh of actual heat, against 7.5p from a heat pump at SCOP 3.5. That's a proper saving, not a rounding error. There's an extra £1,500 on top of the BUS grant until March 2027 if you're on oil or LPG with no mains gas connection, too. See our heat pump vs oil boiler comparison for the full breakdown.
The Verdict
- Boiler 12 years old or more? Heat pump first. The grant plus the boiler you'd have bought anyway makes the real extra cost small, and the timing never gets better than this.
- Boiler nearly new? Solar first. Nine to twelve years to pay back, nothing to think about afterwards, and it improves the heat pump case for later.
- On oil, LPG or electric heating? Heat pump, whatever the state of your boiler. The running cost gap is large enough that the usual arithmetic doesn't apply.
- Can you do both? Do both, together, from one installer if you can find a good one who does both properly.
For the detail behind these numbers, see our heat pump costs guide and solar panel costs guide.