Electric underfloor heating with solar panels: does it make sense?

Pairing solar panels with electric underfloor heating sounds like a perfect match: free electricity from the roof, warm floors below. The physics is simple. Your solar inverter turns the panels' output into normal 230V household electricity, and the heating mat uses whatever electricity is on the circuit. When the panels are generating more than the house is using, the heater runs on solar. When they are not, it runs on the grid or a battery.

What decides whether it makes sense is how much solar is available when the floor is actually on. This guide sets out UK solar output through the year, how to time your heating to use it, where batteries fit, what export payments are worth comparing against, and the VAT rules that catch people out.

Can underfloor heating run on solar panels?

Yes. Electric underfloor heating is a simple resistive load on a normal circuit, so it uses solar electricity the same way a kettle or washing machine does. You do not need a special mat, cable or thermostat.

• During the day, any solar power the house is not already using can run the heater.
• At night or on dull days, the heater draws from the grid, or from a home battery if you have one.
• Water underfloor heating can also benefit, because a heat pump runs on electricity too. See underfloor heating with a heat pump.

The heater itself does not know where the electricity comes from. The savings depend entirely on how much of the heater's use lines up with solar generation.

How much solar will I get when I need the heating?

Much less in winter than in summer. The UK's solar resource is strongly seasonal, and heating demand runs the other way.

Measure	Figure
Daily solar energy on the ground, London, December	0.52kWh/m²
Daily solar energy on the ground, London, July	4.74kWh/m²
Typical UK solar capacity factor	About 10%

A 10% capacity factor means each kilowatt of panels (kWp) produces roughly 850 to 900kWh a year on average across the UK. Most of that arrives between spring and autumn. In December and January, a domestic system produces a small fraction of its summer output, and most of it around midday.

Your own roof will differ with location, direction, pitch and shading. An MCS-certified installer will give you an estimate for your system, and the Energy Saving Trust has a solar calculator for the same job.

How much electricity does an electric heated floor use?

Multiply the heated area by the heater's output. That gives the power drawn while it is on.

Floor	Power while on	2 hours at full power	Grid cost at 26.32p/kWh
4m² at 150W/m²	0.6kW	1.2kWh	about 32p
8m² at 150W/m²	1.2kW	2.4kWh	about 63p
12m² at 150W/m²	1.8kW	3.6kWh	about 95p

The cost column uses Ofgem's average price cap electricity unit rate of 26.32p/kWh for 1 October to 31 December 2026. Once the floor is warm, the thermostat cycles the heater on and off, so real use is often lower than the full-power figure. Our guide to underfloor heating running costs covers this in detail.

A small bathroom floor on a bright spring day could easily run entirely on spare solar. A large kitchen floor on a December evening will run almost entirely on the grid.

How do I get the most solar into my heated floor?

Run the floor when the panels are generating, and make sure the heat stays in the room.

1. Programme for midday. A programmable thermostat such as the Heatmiser neoStat-e runs 5/2 day, 7 day or 24 hour schedules. Set the main heating period across the late morning and early afternoon.
2. Store heat in the floor. A tiled floor holds some warmth after the heater switches off. Warming it at midday carries some of that into the afternoon.
3. Insulate under the heater. Without insulation, much of the heat goes down into the slab. An insulation board under the mat keeps more solar energy in the room. See insulation under underfloor heating.
4. Size the wattage sensibly. A lower-output floor spread over more hours fits the gentle winter solar curve better than a high-output floor run in short bursts. See 100W vs 150W vs 200W electric UFH.
5. Avoid clashes. Washing machines, dishwashers and EV chargers compete for the same midday solar. Stagger them if you can.

Do I need a battery to run underfloor heating on solar?

Only if you want to use daytime solar in the evening. A home battery stores surplus solar and releases it later, for example when you want the bathroom floor warm before bed.

In winter there is often little surplus to store, because the house uses most of what the panels make. A battery helps most in spring and autumn, when the panels produce more than the house needs during the day but evenings are still cool.

What about solar diverters? A solar diverter uses clamps on the supply to detect surplus power and send it to a load instead of exporting it. They are designed for electric water heating through an immersion heater, and the guidance we found does not cover using them for underfloor heating. Ask the diverter maker before connecting one to a heating circuit.

Is it better to export solar or use it for heating?

Using it yourself is usually worth more, because a kWh you do not buy saves the full unit rate. Exporting it earns whatever your export tariff pays.

Under the Smart Export Guarantee, electricity suppliers with at least 150,000 domestic customers must offer at least one export tariff. Ofgem's rules say the rate must be above zero at all times, but each supplier sets its own rate, so they vary widely. To qualify, solar PV up to 50kW must be installed by a certified installer, for example under MCS, and the export must be measured by a meter that can take half-hourly readings.

Compare your export rate with your import rate. If you are paid a few pence to export but pay about 26p to import, every kWh the heated floor uses from your own panels is worth the import rate.

Is there 0% VAT on solar panels and underfloor heating?

There is 0% VAT on installed solar panels, home batteries and smart diverters in homes until 31 March 2027, but not on electric underfloor heating, and not on any kit you buy without installation.

• What qualifies. HMRC's energy-saving materials list includes solar panels, insulation for floors, central heating and hot water controls, heat pumps, and from 1 February 2024 electrical storage batteries and smart diverters.
• Installed only. The zero rate applies only where a business supplies and installs qualifying materials in residential accommodation. Goods supplied without installation, including sales by retailers and merchants, are standard-rated at 20%.
• Dates. The zero rate covers installations from 1 May 2023 to 31 March 2027. From 1 April 2027 these installations move to the 5% reduced rate.
• Electric underfloor heating is not on the list, so a mat and cable are standard-rated however they are supplied.

MaxHeatUFH sells supply only, and charges 20% VAT on every product. If you buy heating mats, insulation boards or thermostats from us, or from any merchant, the price includes 20% VAT. Check the full rules in HMRC's VAT Notice 708/6 before you rely on any relief.

Electric underfloor heating with solar or a heat pump: which is better?

For one or two small rooms, electric underfloor heating with solar is simple and cheap to install. For a whole house, water underfloor heating with a heat pump is the option to compare it with, because it runs at low flow temperatures and can be zoned across many rooms. Solar panels can help both, since a heat pump also runs on electricity.

Our guide to water vs electric underfloor heating compares the two, and is underfloor heating worth it? covers the wider picture.

Whatever you choose, the electrics matter. Electric underfloor heating needs a 30mA RCD and a final connection by a qualified electrician to BS 7671, under Part P in England and Wales. Solar PV should be fitted by a certified installer, which is also what you need to claim export payments.

Products for this job

• Electric Underfloor Heating Mat 100W/m²
• Electric Underfloor Heating Mat 150W/m²
• Heatmiser neoStat-e smart thermostat
• Heatmiser neoHub G3, for app control
• Cement-Coated XPS Tile Backer Board
• All electric underfloor heating

Frequently asked questions

Can solar panels power underfloor heating at night?

Not directly. Panels only generate in daylight. To use solar at night you need a home battery, otherwise the heater runs from the grid.

Will solar panels make my underfloor heating free to run?

Not in winter. UK solar output in December is a small fraction of summer output, so most winter heating comes from the grid. Spring and autumn are when solar covers the most.

Do I need a special thermostat for solar?

No. Any suitable floor-sensing thermostat works. A programmable or smart one helps you schedule the heating for the middle of the day, when panels generate most.

How many solar panels do I need for underfloor heating?

There is no fixed number, because the floor shares the panels with everything else in the house. A 4m² floor at 150W/m² draws 0.6kW while on. Ask an MCS installer for a generation estimate for your roof and compare it with your total use.

Is there 0% VAT on electric underfloor heating?

No. Electric underfloor heating is not an energy-saving material for VAT. Installed solar panels, batteries, floor insulation and heating controls can be zero-rated until 31 March 2027, but only when a business supplies and installs them in a home.

Can I use a solar diverter for underfloor heating?

Diverters are designed for immersion heaters. Check with the diverter maker before connecting one to a heating circuit.

Is it better to export my solar or heat my floor with it?

Using it yourself usually saves more, because you avoid buying electricity at the full unit rate. Export tariffs vary by supplier, so compare your rates.

Sources: Solar power in the United Kingdom (irradiance and capacity factor), Ofgem price cap unit rates, Ofgem Smart Export Guarantee generator guidance, HMRC VAT Notice 708/6, Energy Saving Trust solar energy calculator