SOLAR GUIDE
Solar Water Heater 2026: Cut Your Hot Water Bills
A solar water heater uses roof-mounted panels to heat your domestic hot water, cutting those bills by 50-70% between April and September.
A solar water heater uses roof-mounted panels to heat your domestic hot water, cutting those bills by 50-70% between April and September.
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A solar water heater uses roof-mounted panels to heat your domestic hot water, cutting those bills by 50-70% between April and September. Systems cost £3,000 to £5,000 installed, and while the Boiler Upgrade Scheme doesn't cover solar thermal directly, ECO4 may fund it for eligible households. Most south-facing homes with a conventional hot water cylinder are suitable.
£80 to £120 a year. That's roughly what the average UK household spends just heating water for showers, baths, and taps, according to the Energy Saving Trust. A solar water heater captures free energy from the sun and uses it to pre-heat that water before your boiler or immersion heater has to do anything.
The basic principle is simple. Panels on your roof absorb sunlight and transfer that heat to a fluid (usually a glycol mix, like antifreeze) circulating through them. This fluid passes through a coil inside your hot water cylinder, warming the stored water. Your existing boiler or immersion heater tops up the temperature when the sun hasn't done enough, so you never run out of hot water.
Two types of panel dominate the UK market:
Flat plate collectors. These look like dark rectangular panels, similar to solar PV but thicker. They're cheaper (£2,500 to £4,000 installed) and work well on most roofs. Vaillant and Kingspan are the names you'll see most often.
Evacuated tube collectors. These use rows of glass tubes, each containing a vacuum that reduces heat loss. They're more efficient in cloudy conditions and cost £3,500 to £5,000 installed. They look distinctive, almost like a row of test tubes laid flat on your roof.
Here's what most guides won't tell you: in summer, a well-sized system will heat all your water without the boiler firing at all. In winter, it'll pre-heat the water from maybe 8°C to 20-25°C, so your boiler only has to do half the work. The annual contribution is typically 50-70% of your hot water needs, not 100%. Anyone who tells you otherwise is selling something.
One quick digression: solar thermal was actually more popular than solar PV in the UK before about 2012. The Feed-in Tariff made PV far more financially attractive, and solar thermal installations dropped off a cliff. But the technology hasn't gone anywhere, and with current gas prices, the payback maths is looking better than it has in a decade. Anyway.
Savings depend on what you're replacing and how much hot water your household uses. A family of four using gas to heat water will save differently from a couple using an electric immersion heater.
For gas-heated homes, the Energy Saving Trust estimates annual savings of £55 to £95 per year at current tariff rates. That's not life-changing. Honestly, if you're on mains gas and your boiler is relatively new, the financial case for solar thermal alone is weak. The payback period stretches to 35-50 years.
But here's where it gets interesting.
If you heat water with electricity, whether that's an immersion heater, an old electric boiler, or you're off the gas grid entirely, savings jump to £150 to £300 a year depending on your tariff. Payback drops to 12-20 years, which is within the 25-year lifespan of most systems.
And if you combine solar thermal with a heat pump installation, the system pre-heats water before the heat pump's cylinder coil takes over, reducing the heat pump's electricity consumption. Some installers report 15-20% reductions in heat pump running costs when solar thermal is part of the setup.
The real sweet spot? Homes that are off the gas grid, using oil or LPG for heating, where fuel costs are already high and delivery is unpredictable. We see these households benefiting most from solar thermal as part of a wider energy upgrade.
Right, so here's the slightly frustrating bit. Solar thermal doesn't have a dedicated grant scheme the way heat pumps do.
The Boiler Upgrade Scheme (BUS) covers heat pumps and biomass boilers but not solar water heating systems. You can't claim the £7,500 towards a solar thermal installation. If you're considering a heat pump alongside solar thermal, the BUS grant applies to the heat pump portion only.
ECO4 is a different story. Under ECO4, which runs until December 2026, energy suppliers fund energy efficiency measures for low-income and vulnerable households. Solar water heating is listed as an eligible measure, though in practice it's less commonly installed than insulation or new heating systems. Whether your supplier will fund it depends on the deemed score improvement it brings to your specific property. If you're on benefits like Universal Credit, Pension Credit, or Child Tax Credit, it's worth checking. We've covered ECO4 eligibility in detail separately.
The Warm Homes: Local Grant is another possibility. This scheme, running until 2028, is administered by local authorities and the measures funded vary by area. Some councils include solar thermal in their eligible upgrades. Others don't. You'd need to check with your specific local authority or use an eligibility checker to see what's available at your postcode.
One thing to note: VAT on solar thermal installations is 0% for residential properties, just as it is for solar PV panels. That saves you £500 to £1,000 compared to the full 20% rate. No application needed. Your installer just charges the lower rate.
This is the question we get asked most. And the honest answer is: for most homes in 2026, solar PV is the better investment.
That's not because solar thermal doesn't work. It does, and it's actually more efficient per square metre at converting sunlight into usable energy. But PV has several practical advantages that have tipped the balance:
Solar PV generates electricity you can use for anything, not just hot water. With a diverter (a device that sends surplus electricity to your immersion heater), PV can heat your water AND power your appliances, lights, and EV charger. Solar thermal only heats water. Full stop.
PV panels are cheaper per kW than they were five years ago. A typical 4kW system costs £5,000 to £7,000 and offsets a much larger portion of your total energy bill.
PV qualifies for the Smart Export Guarantee, meaning you get paid for surplus electricity. Solar thermal has no equivalent payment scheme.
So when does solar thermal still make sense?
If you're starting from scratch with a blank roof and a decent budget, we'd suggest looking at whether solar PV is worth it for your situation first. Solar thermal works best as a complement to other systems, not as a standalone investment.
Not every home works. Here's what you need:
A south-facing roof (or within 45° of south) with minimal shading. East or west facing can work but reduces output by 15-20%. North-facing is a non-starter.
Roof space for the panels. Flat plate collectors need about 3-4m² for a typical household. Evacuated tubes need slightly less, around 2-3m². If your roof is cluttered with dormers, velux windows, or satellite dishes, you might struggle.
A hot water cylinder. This is the deal-breaker for many homes. If you have a combi boiler with no cylinder, you'd need to install one (£500 to £800 for the cylinder plus plumbing modifications). Combi boilers heat water on demand and have nowhere to store solar-heated water. You need that storage tank.
About 40% of UK homes now have combi boilers, according to BEIS data. That's a lot of properties where solar thermal requires additional work before it's even viable.
Pipe runs matter too. The shorter the distance between your roof panels and your cylinder, the less heat you lose in transit. A cylinder in the loft or on the first floor directly below the panels is ideal. A cylinder in a ground-floor kitchen with panels three storeys up? Less ideal, though insulated pipe runs can manage it.
Your EPC rating won't directly affect whether you can install solar thermal, but it will affect grant eligibility. Properties rated D or below typically score better for funded improvements under ECO4.
Look for MCS certification. This isn't optional. MCS (Microgeneration Certification Scheme) is the industry standard, and any grant funding requires an MCS-certified installer. It also ensures your system meets quality standards and that your installer carries appropriate insurance.
Get three quotes. Prices vary significantly. We've seen identical systems quoted at £3,200 and £4,800 by different companies in the same city. The difference is often labour costs and margins, not equipment quality.
So what happens on installation day?
The job typically takes one to two days. Day one involves mounting the panels on your roof (scaffolding usually goes up the day before), running the pipework from roof to cylinder, and fitting the pump station and controller. Day two, if needed, involves connecting everything, filling the system with glycol fluid, pressurising it, and commissioning.
Your existing hot water cylinder may need replacing with a twin-coil model. One coil connects to your boiler (or heat pump), the other to the solar panels. If you already have a twin-coil cylinder, you're in luck. If not, factor in an extra £400 to £700 for the cylinder swap.
After installation, maintenance is minimal. An annual check of the glycol fluid levels and system pressure is recommended. The glycol should be replaced every 5-7 years (about £100 to £150 each time). Panels themselves have no moving parts and typically last 25 years or more.
One thing to ask your installer: what happens in summer when you're producing more hot water than you can use? Good systems have a dump valve or the controller stops the pump to prevent overheating. Cheap installations sometimes skip this, leading to glycol degradation and premature system failure. Ask specifically how overheating protection works.
Common questions