How Many Solar Panels Do I Need for Underfloor Heating?
For most UK homes, you’ll need somewhere between 8 and 16 solar panels to power underfloor heating, though smaller setups can work with as few as 6 panels and larger properties may need 20 or more.
The exact number of solar panels you need for underfloor heating depends on several factors, including the size of your home, the type of underfloor heating system you have, and how much of your heating you want solar to cover.
This guide walks you through everything you need to know, in plain English, so you can make a smart, informed decision for your home.
How many solar panels do you need to run underfloor heating?
The number of solar panels you need to run underfloor heating typically ranges from 8 to 16 panels for an average UK home, but this number can vary quite a bit depending on your specific situation.
What size solar panel system do you need for underfloor heating?
The size of the solar panel system you need for underfloor heating is usually between 3 kWp and 8 kWp for most homes. Here’s how that translates into panels:
Most modern residential solar panels are rated between 350 watts and 450 watts. Using 400 watts as a standard:
- A 3 kWp system = approximately 7 to 8 panels
- A 4 kWp system = approximately 10 panels
- A 5 kWp system = approximately 12 to 13 panels
- A 6 kWp system = approximately 15 panels
For a medium-sized home in Bristol, Southampton, or South Wales running electric UFH across most of the ground floor, a 5 to 6 kWp system with a 10 kWh battery is a commonly recommended starting point.
How to calculate the right number of solar panels for underfloor heating
Calculating the right number of solar panels for underfloor heating involves a few straightforward steps:
- Work out your UFH energy consumption: Multiply the wattage per square metre by the total floor area you want to heat, then estimate daily usage hours.
- Factor in your other household energy use: Solar panels will also power your lights, appliances, and other devices, so it makes sense to size the system for your whole home.
- Check your roof’s suitability: A site survey will confirm how much roof space you have, its orientation, and whether any shading from trees or chimneys might affect output.
- Calculate required solar output: Divide your daily energy needs by the average daily output per panel in your area.
- Add battery storage: Choose a battery size that bridges the gap between when your panels generate electricity and when you actually need it.
This is exactly the kind of assessment a professional solar installer like EE Renewables will carry out before recommending a system. No two homes are the same, and a bespoke system design makes a real difference to performance and payback.
What factors affect the number of solar panels needed for underfloor heating?
Several key factors affect how many solar panels you need for underfloor heating, and understanding them will help you avoid undersizing or oversizing your system. Here’s what you need to consider.
Your type of underfloor heating system
The type of underfloor heating system you have plays a big role in determining how many panels you’ll need, because electric and water-based systems have very different energy demands.
Electric underfloor heating uses heating mats or cables installed beneath your floor. It runs directly off your home’s electricity supply, which makes it straightforward to power with solar panels. A typical electric UFH system in a single room might consume around 100 to 200 watts per square metre. So if you’re heating a 20 square metre kitchen, you could be looking at 2,000 to 4,000 watts (2 to 4 kW) just for that one room.
Wet underfloor heating uses warm water pumped through pipes beneath the floor and is usually connected to a heat pump or boiler. If you’re running it with an air source heat pump, the electricity demand is lower than electric UFH because heat pumps are very efficient, typically producing 3 units of heat for every 1 unit of electricity. If you’re running wet UFH with a gas boiler, solar panels won’t directly power the heating itself, though they can still power the pump and controls.
For most homeowners in Southern England and South Wales considering solar-powered UFH, electric underfloor heating paired with solar panels and a battery storage system tends to be the most practical and cost-effective setup.
The size of your home
The size of your home and the floor area you want to heat is one of the biggest factors in determining how many panels you need. Here’s a general guide based on heating the whole ground floor of a UK home:
- Small home (up to 80 sqm): 6 to 8 solar panels
- Medium home (80 to 120 sqm): 8 to 12 solar panels
- Larger home (120 to 200 sqm): 12 to 16 solar panels
- Large detached home (200 sqm+): 16 to 20+ solar panels
Keep in mind these figures assume you want solar to cover a significant portion of your underfloor heating energy use. If you’re happy with solar supplementing your heating rather than covering it entirely, you could get away with fewer panels.
Your home’s insulation
Your home’s insulation levels have a direct impact on how many solar panels you need, because a well-insulated home requires far less energy to stay warm. When your underfloor heating works less hard, your solar panels go much further.
On the other hand, if your home has solid walls with no insulation, older single-glazed windows, or a poorly insulated loft, you’ll need significantly more energy to maintain a comfortable temperature, which means more panels.
Before investing in solar for underfloor heating, it’s worth making sure your home is as energy-efficient as possible. Simple improvements like loft insulation, double glazing, and draught-proofing can dramatically reduce how hard your UFH system has to work.
This is especially relevant for older properties in areas like Brighton, Oxford, and Cardiff, where Victorian and Edwardian terraced houses are particularly common and can lose a lot of heat without proper insulation.
Roof orientation
Absolutely. A south-facing roof at a pitch of around 30 to 40 degrees will generate the most electricity from your panels. East or west-facing roofs generate roughly 15 to 20% less energy. A north-facing roof is not suitable for solar panels.
If your roof doesn’t face south, you may need to install additional panels to compensate for the lower output. A good installer will assess your roof orientation during a site survey and factor this into the system design.
How many kWh does underfloor heating use per day?
Underfloor heating uses roughly 10 to 30 kWh per day depending on the size of the heated area, how well-insulated your home is, and the outside temperature. Breaking this down further:
- A small electric UFH system in a bathroom or kitchen (5 to 10 sqm) might use just 1 to 3 kWh per day
- A medium ground floor installation (50 to 80 sqm) could consume 10 to 20 kWh per day
- A whole-home electric UFH system in a larger property might use 25 to 40 kWh on a cold winter’s day
Understanding your daily energy consumption is crucial to sizing your solar panel system correctly. A good solar installer will calculate your likely usage and size the system accordingly, factoring in the solar irradiance levels specific to your location in the UK.
Average daily solar output in the UK
UK solar panels generate less electricity than those in sunnier climates, but they still perform well, particularly in the south of England. On average, a single 400-watt solar panel in Southern England generates around:
- Summer: 1.5 to 2.5 kWh per day
- Winter: 0.3 to 0.8 kWh per day
- Annual average: Around 1 to 1.2 kWh per day
This seasonal variation is important. If you’re planning to run underfloor heating primarily in winter, your solar panels will produce less power precisely when you need it most. This is where a solar battery storage system becomes essential.
Can solar panels power underfloor heating year-round in the UK?
Solar panels can contribute to powering underfloor heating year-round, but they are unlikely to cover 100% of your heating needs during the winter months on their own. During summer and spring, a well-sized solar system with battery storage can easily meet or exceed the energy needed to run UFH.
During the winter, particularly in December and January, shorter daylight hours and lower sun angles mean your panels produce significantly less electricity.
A realistic expectation for most homeowners in London, Cardiff, or Brighton is that solar panels might cover:
- 60 to 80% of underfloor heating energy in spring and autumn
- 80 to 100% during summer months
- 10 to 30% during mid-winter
The remaining shortfall during winter can be covered by importing electricity from the grid, ideally on an economy tariff or a smart tariff like Octopus Agile, which allows you to charge your battery when electricity is cheapest (usually overnight).
Do you need a solar battery to run underfloor heating?
Yes, a solar battery storage system is strongly recommended if you want to use solar panels to power underfloor heating effectively. Here’s why:
Underfloor heating is typically used most during the evening and overnight, when solar panels aren’t generating any electricity. A solar battery allows you to store the electricity generated during daylight hours and use it later in the day when your heating is running.
Without a battery, any excess solar energy your panels produce during the day gets exported back to the grid, and then you’d have to buy electricity from your supplier to run your underfloor heating in the evening. That’s not an efficient setup if your goal is to cut energy bills.
Recommended Battery Size for UFH
For a home running electric underfloor heating, a battery capacity of 5 to 15 kWh is typically recommended. Popular solar batteries used in UK homes include the Tesla Powerwall, GivEnergy, and SolarEdge systems. Your installer should recommend a battery size that matches both your solar panel output and your expected heating demand.
Is it worth installing solar panels for underfloor heating?
Installing solar panels for underfloor heating is absolutely worth it for the right home, and the financial case is stronger than ever right now. Here’s why homeowners across Southern England and South Wales are making the switch:
Lower energy bills
Electricity prices in the UK have risen significantly in recent years. Running electric underfloor heating on grid electricity is expensive. Solar generation reduces how much electricity you buy from the grid, which directly cuts your bills.
Smart Export Guarantee (SEG) payments
When your solar panels produce more electricity than you’re using, the excess is exported to the grid. Under the UK government’s Smart Export Guarantee (SEG) scheme, your energy supplier pays you for every unit you export. This provides an additional income stream that helps offset the cost of installation.
Increased property value
Homes with solar panels and battery storage are increasingly attractive to buyers. A solar-equipped home in London, Bristol, or Southampton typically commands a higher asking price and sells faster than a comparable home without solar.
Typical payback period
For a combined solar and battery system designed to support underfloor heating, the payback period in the UK typically ranges from 6 to 12 years, depending on system size, energy usage, and local electricity prices. With panels expected to last 25 to 30 years, that’s a substantial period of free or near-free electricity.
Ready to get a free solar quote for UFH?
At EE Renewables, we install solar panel systems and solar battery storage across Southern England, Greater London, South West England, and South Wales, including London, Brighton, Oxford, Southampton, Bristol, and Cardiff. Whether you’re planning to power underfloor heating or simply want to reduce your energy bills, we can design a system that works for your specific home and location.
Get your free, no-obligation quote from EE Renewables today.
Frequently Asked Questions
Can I run underfloor heating entirely on solar panels without any grid connection?
Running underfloor heating entirely off-grid is possible but challenging in the UK, particularly through winter. You would need a very large solar array (potentially 20 or more panels), a large battery bank, and possibly a backup generator for extended periods of low sunlight. Most UK homeowners opt for a grid-connected solar system with battery storage instead, which is far more cost-effective and practical.
Does underfloor heating work well with an air source heat pump and solar panels together?
Yes, this is actually one of the most efficient combinations for home heating. An air source heat pump running wet underfloor heating uses electricity very efficiently, and solar panels can power a significant portion of that electricity demand. The lower flow temperatures required by underfloor heating (around 35 to 45°C) are ideal for heat pump operation, making this a well-matched pairing.
Will solar panels for underfloor heating still work during a power cut?
Standard grid-tied solar panel systems switch off automatically during a power cut for safety reasons. However, if you have a solar battery with islanding or backup capability (such as the Tesla Powerwall), your system can continue to power your home, including your underfloor heating, during an outage.
Do I need planning permission to install solar panels for underfloor heating in the UK?
In most cases, solar panels are considered permitted development in England and Wales, meaning you don’t need planning permission. However, there are exceptions, such as if your home is a listed building or in a designated Area of Outstanding Natural Beauty (AONB) or conservation area. Your installer will be able to advise you during the initial consultation.
How long does it take to install a solar panel system for underfloor heating?
A typical residential solar panel and battery storage installation takes one to two days to complete. The process involves mounting the panels on your roof, installing the inverter and battery system, connecting to your consumer unit, and completing the necessary electrical checks. After installation, your system can begin generating electricity immediately.
