How Many Solar Panels Do I Need for Underfloor Heating?

Underfloor heating is a popular choice for homeowners and landlords across the UK seeking energy-efficient, evenly distributed warmth. But with energy prices rising and sustainability high on the agenda, many are turning to solar power to run their underfloor systems. 

In this guide we’ll cover the number of solar panels needed to run underfloor heating, from energy requirements to installation considerations, so you can make an informed investment.

How Many Solar Panels Are Required to Run Underfloor Heating in the UK?

To power an average electric underfloor heating system in the UK, you will typically need between 6 and 35 solar panels, depending on the size of the area being heated and the wattage of the panels installed. 

Most UK homes use 350W to 420W solar panels, so for example, a 20m² electric underfloor system would require around 12 to 16 panels, assuming typical usage during winter.

The number of solar panels you need depends on several key factors:

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  The type of underfloor heating (electric vs water-based)
  
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  The total heated floor area (in m²)
  
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  The insulation quality of the property
  
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  Location and average sun hours (solar irradiance)
  
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  The power rating and efficiency of your solar panels

Here’s a general breakdown for electric underfloor heating, which is more energy-demanding:

Note: Figures are based on 6–8 hours of daily usage during winter months. Assumes average annual solar yield in the UK of 850–1,000 kWh per installed kW, per Energy Saving Trust.

How to Calculate the Number of Solar Panels Needed to Run Underfloor Heating

Let’s say you have a 40m² electric underfloor heating system, consuming 5,400 kWh per year.

If each panel produces:

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  350W panel = ~298 kWh/year
  
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  400W panel = ~340 kWh/year
  
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  420W panel = ~357 kWh/year

You would need:

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  5,400 ÷ 298 = ~18 panels (350W)
  
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  5,400 ÷ 340 = ~16 panels (400W)
  
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  5,400 ÷ 357 = ~15 panels (420W)

However, keep in mind:

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  You may not use underfloor heating year-round.
  
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  Other household appliances can share the solar-generated electricity.
  
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  Solar production varies seasonally, winter output is significantly lower.
  
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  Battery storage helps store surplus summer electricity for use in winter.

Tip: Installing battery storage can help you store excess summer generation for winter use.

What Influences the Number of Solar Panels You Will Need?

1. Type of Underfloor Heating

There are two main types of underfloor heating in the UK:

Electric (dry) systems

Electric underfloor heating systems use resistive cables or heating mats beneath the floor. They run directly on electricity and are energy-intensive, typically consuming 150–200 watts per square metre. 

This means you’ll need a large solar PV system and possibly a battery to run it effectively.

Water-based (wet) underfloor heating systems

Water-based (wet) underfloor heating systems circulate warm water through pipes installed beneath the floor. The water needs to be heated by a separate heat source, such as a boiler or heat pump.

These systems are more energy-efficient than electric underfloor heating, and they can be integrated with solar energy, but the type of solar system (solar PV vs solar thermal panels) and type of boiler you have make a big difference in compatibility.

Can You Use Solar PV with Water-Based Underfloor Heating?

Yes, but only in specific setups.

Solar PV panels generate electricity, not heat. That electricity can be used to power electric boilers, air source heat pumps, or to heat a hot water cylinder. But if your boiler uses gas and you don’t have a hot water tank, solar PV won’t work for your heating system.

Let’s break it down:

Solar PV vs Solar Thermal for Wet Underfloor Heating

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  Solar PV can support water-based heating systems indirectly, but only if you have an electric-compatible heating system with a hot water storage tank.
  
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  Solar Thermal, on the other hand, is designed to directly heat your water, making it far more efficient for wet systems, especially when your goal is to reduce grid reliance in colder months.

According to the Energy Saving Trust, solar thermal can meet up to 60% of a home's hot water demand annually, especially in spring and summer.

Recommendation: Combine Solar Thermal and Solar PV for Maximum Efficiency

If you're upgrading or installing a wet underfloor system and want to reduce your reliance on fossil fuels:

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  Use solar thermal to preheat water for your heating system.
  
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  Use solar PV to power the electric components (such as heat pumps or immersion heaters).

If you're currently using a gas combi boiler without a hot water tank, you'll need to upgrade your system, either by switching to a system boiler with a tank, a heat pump, or an electric combi boiler to make full use of solar energy.

2. Solar Panel Efficiency

Not all solar panels are created equal. Panel efficiency affects how much energy a given area of your roof can produce.

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  Higher-efficiency panels (like 400W+ monocrystalline models) generate more power in limited roof space.
  
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  Lower-efficiency panels may require more surface area to generate the same amount of electricity.

Also, over time, panels degrade slightly, so factor in long-term performance when sizing your system.

3. Property Location

The amount of solar energy (solar irradiance) your property receives varies depending on which part of the UK you live in. 

This directly affects how much electricity your solar panels can produce, and therefore how many panels you’ll need to run your underfloor heating.

Here’s a general breakdown of average solar irradiance by region:

In general:

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  Southern regions benefit from stronger and more consistent sunlight, meaning they require fewer solar panels to generate the same amount of electricity.
  
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  Northern and western regions, including much of Scotland and parts of Wales, tend to receive less solar irradiance annually, so you may need to install more panels or supplement your system with battery storage.

Example: A home in the South East may only need 12 panels to meet heating needs, while a similar home in the North East might need 14–16 to generate the same output.

Proper system sizing based on your location is key to ensuring year-round performance, especially if you rely on solar during the darker winter months when underfloor heating demand is highest.

4. Roof Orientation & Shading

The position and exposure of your roof have a major impact on panel performance:

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  South-facing roofs get the most sun exposure throughout the day, maximising output.
  
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  East or west-facing roofs still work well but may require 10–20% more panels to compensate for reduced sunlight hours.
  
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  Shading from nearby trees, chimneys, or buildings can significantly reduce efficiency. A professional installer can run a solar shading analysis to identify trouble spots.

Tip: Consider microinverters or optimisers if partial shading is unavoidable. These help individual panels perform better, even when others are shaded.

5. Insulation Quality

Before investing in solar panels, it’s vital to check your home’s insulation. Poorly insulated homes leak heat quickly, meaning your underfloor system will need to work harder, and consume more energy.

Improving your insulation can reduce heating demand by up to 45% in older homes.

Well-insulated homes:

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  Maintain heat more effectively
  
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  Require fewer solar panels
  
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  Make better use of energy-efficient systems like heat pumps or solar thermal

6. Seasonal Changes

Solar panels generate more electricity in summer than in winter, which is when you’ll need underfloor heating the most.

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  In June/July, panels can operate at or near peak capacity.
  
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  In December/January, output drops by 70–80% in some regions.

This means that even a well-sized system may fall short during peak heating season unless:

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  You oversize your solar array to account for winter use, or
  
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  You install battery storage to store summer excess for winter use

Tip: If budget allows, consider combining solar with an air source heat pump and thermal store (buffer tank). This ensures more efficient use of solar energy year-round.

How Much Do Solar Panels Cost for Running Underfloor Heating?

The cost of solar panels to run underfloor heating varies and depends on whether you go for solar PV or solar thermal, and which type of underfloor heating you use.

Cost of Solar PV for Underfloor Heating

Note: Not suitable for homes with gas combi boilers unless switching to electric heating or a hybrid setup.

Cost of Solar Thermal for Underfloor Heating

Ideal for wet underfloor heating and homes with a compatible hot water tank.

Solar PV vs Solar Thermal: Cost Comparison Table

How Does Battery Storage Impact How Many Solar Panels You’ll Need?

Underfloor heating is often needed when the sun isn’t shining, especially during winter mornings or evenings. Battery storage systems like the Tesla Powerwall or GivEnergy units allow you to store surplus solar power and discharge it when needed.

Without a battery, much of your solar generation will be exported to the grid when you're not home, and you'll still draw from the grid during peak heating hours. 

A typical UK household uses 30–50% of its generated solar power, but with a battery, that can jump to 80% or more.

Insight: Read our guide on battery system costs and whether it's worth it for your setup.

How Much Roof Space Do You Need for Solar Panels?

Roof space is a crucial consideration when planning solar for underfloor heating. The number and type of panels you install will directly affect how much space you’ll need and how many panels will fit on your roof.

Each solar panel takes up a certain amount of space depending on its wattage and efficiency. Here's how it breaks down:

Roof Space Requirements by Panel Wattage

Figures assume optimal panel placement (south-facing, unshaded roof, ~30° tilt). If your roof is shaded or not ideally oriented, you may need additional panels to compensate.

What If You Don’t Have Enough Roof Space?

If your roof can’t accommodate the number of panels required:

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  Choose higher-wattage or more efficient panels to generate more energy in less space.
  
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  Consider ground-mounted systems if you have suitable land nearby.
  
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  Use a hybrid approach: Solar thermal panels (which require less space) can handle heating duties, while fewer PV panels support electricity needs.
  
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  Incorporate battery storage to spread usage more effectively, reducing peak demand on your system.

What Is the Return on Investment (ROI) for Solar Panels and Solar Thermal Systems for Underfloor Heating?

Investing in solar energy to power your underfloor heating can lead to significant savings, but understanding the return on investment (ROI) helps set clear expectations on costs versus long-term benefits.

How Is ROI Calculated?

ROI measures how quickly your initial investment in solar technology pays back through energy bill savings and possible income from incentives (like the Smart Export Guarantee). It considers:

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  Upfront costs (purchase and installation)
  
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  Energy savings (reduced electricity or gas bills)
  
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  Incentives and grants
  
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  Maintenance and lifespan of the system

Expected ROI for Solar PV Systems

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  Typical payback period: 7 to 12 years for a residential solar PV system powering electric underfloor heating, depending on system size, energy usage, and solar irradiance.

Factors affecting ROI:

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  Your location’s sunlight levels (southern England offers quicker ROI than northern Scotland)
  
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  Electricity prices (higher prices mean greater savings)
  
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  Usage patterns (running heating when solar generation is high improves ROI)
  
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  Battery storage can improve self-consumption but adds to upfront costs

Expected ROI for Solar Thermal Systems

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  Typical payback period: 5 to 10 years, often shorter than solar PV because solar thermal is more efficient at directly heating water.

Factors affecting ROI:

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  How well insulated your home is (better insulation means less heat loss and more savings)
  
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  Your current heating system and fuel costs (solar thermal reduces reliance on gas or electric boilers)
  
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  The size of the solar thermal array and your hot water usage
  
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  Maintenance costs, which are generally low but can include occasional servicing of pumps and controllers

Additional Considerations

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  Solar panels typically have a warranty of 25 years and can last 30+ years with minimal efficiency loss.
  
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  Solar thermal systems also have warranties around 20–25 years.
  
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  Combining solar PV and solar thermal with energy efficiency upgrades (like insulation or smart thermostats) accelerates ROI.
  
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  Rising energy costs increase the value of solar investments, making solar systems more financially attractive over time.

Estimated Savings from Running Underfloor Heating with Solar PV or Solar Thermal

Are There Government Grants & Financial Incentives for Solar Panel Installation in the UK?

When considering solar panels for underfloor heating, it’s important to know what grants and financial incentives are available across the UK. These schemes can help reduce the initial cost or provide ongoing financial benefits.

Grants Available for Solar Panel Installation

1. ECO4 Scheme

The Energy Company Obligation (ECO4) scheme helps low-income and vulnerable households install energy-saving measures, including solar PV panels. 

If you qualify based on income or benefits, you may get free or subsidised solar panel installation to reduce your energy costs. Eligibility often depends on your home’s energy efficiency rating (EPC) and income level.

2. Local Authority Delivery Schemes

Some local councils across the UK offer their own grants or green home improvement schemes that support solar panel installations, often focusing on low-income or fuel-poor households. These vary widely by region, so checking with your local authority is advised.

Financial Incentives for Solar Panel Owners

1. Smart Export Guarantee (SEG)

Under the Smart Export Guarantee (SEG), you can earn money by selling any surplus electricity generated by your solar PV system back to the national grid. 

Multiple licensed energy suppliers offer tariffs, and you must have a smart meter installed. This helps reduce your electricity bills and makes your solar investment more profitable.

2. VAT Reduction on Solar Panel Installation

The UK government has reduced the VAT on domestic solar panel installations (both PV and thermal) to 0% until March 2027. This means you pay no VAT on the cost of the panels and their installation, lowering upfront costs.

Compare Solar Quotes Tailored to You

Compare solar quotes for your home and heating setup. Use the Eco Answers Quote-Comparison Tool. It’s free, fast, and connects you with trusted UK suppliers offering competitive quotes tailored to your property.

FAQs

1. Can I power underfloor heating solely with solar panels year-round in the UK?

In most cases, no. Due to lower winter solar output, most homes will need grid backup or battery storage to meet full demand in colder months.

2. Do solar panels need direct sunlight to work?

No, solar panels do not need direct sunlight to work. Panels still generate electricity on cloudy days, although output is lower. Modern panels are efficient enough to work in typical UK weather.

3. Are solar panels suitable for listed buildings with underfloor heating?

Installation is more complex and requires planning permission, but it is possible with ground-mounted systems or specially approved roofing solutions.

4. Is it better to install solar panels before or after underfloor heating?

Ideally, plan both together. This allows better energy modelling and may reduce total system cost.

5. Will I still receive a bill from my energy provider if I install solar panels?

Yes. Unless you install an off-grid system, you will remain connected to the grid and may still use energy from your supplier, especially in winter.

Our Verdict

Using solar panels to power underfloor heating in the UK is a sustainable and potentially cost-saving decision, especially when paired with battery storage. The number of panels you need depends on your home’s energy demand, panel efficiency, and your location in the UK. 

With rising energy prices and increasing support for renewables, now is a great time to invest in solar.

Don’t guess your requirements. Use the Eco Answers Quote-Comparison Tool to get matched with the right system, tailored to your property. It’s free, simple, and connects you with reliable, accredited UK installers.