DIY Solar Pool Heater vs an Installed System

The short answer

A DIY solar mat kit costs about £120–£310 and can take the chill off a small or sheltered pool, but one 0.66m by 6m mat is only about 4m², and the trade body SPATA says collector area for pool heating usually exceeds half the pool surface. An 8×4m pool has 32m² of surface, so it wants about 16m² of collector: four or five mats, more than any kit we found. On the one independent UK measurement we found, a kit this size could still pay back quickly, but the numbers carry real caveats, set out below.

What a kit can plausibly deliver

The retailer's page claims a 3–5°C rise per day and a manufacturer test taking a small pool from 20°C to almost 36°C in two to three days, with no conditions given. We treat that as marketing. The independent evidence is a European Commission monitoring project on eight English pools run in 1982–84, which recorded about 300kWh of heat per square metre of collector over an outdoor season, at pool temperatures of 21–24°C and collector efficiencies of 20–50%. That is old data on cooler pools than the 28°C our examples use, so read it as an optimistic guide.

On that figure a three-mat kit (about 12m²) delivers about 3,600 kWh of heat a season, worth about £330 if it displaces gas at 9.4p per kWh of heat (7.97p at 85% efficiency, Ofgem cap October to December 2026), or about £940 if it displaces direct electric heating at 26.32p. Against a £310 kit that is a payback of about a year on gas, and under a season on direct electric heating, if the old figure holds. Even three mats cover only a third of an 8×4m pool's surface, so expect a few degrees of help rather than a heated pool; a larger array of the same mats scales the saving up to roughly £450 a season at 16m² on gas.

What a kit will not do

It will not hold a temperature. The kits we found pump through the mats whenever the small panel makes enough power, with no thermostat in the listings, so on a hot day it will keep heating a pool that is already warm and at night with the pump stopped it does nothing. It will not extend the season by a fixed amount: we found no independent UK figure for temperature gain or season extension. And it will not do anything for the house: unlike photovoltaic panels, mats have no value from October to April. The PV vs solar thermal comparison sets out when each route makes sense.

When to pay for an installed system

• The pool is large. Above about 30m² of surface the collector area needed is more than a kit covers, and an installer can size against the pool volume and the roof.
• You want a temperature, not a trend. A controller and diverter valve stop the roof circuit when it is not helping.
• The roof is awkward. Fixings, plumbing runs and wind loading are where DIY jobs go wrong.
• You want year-round value. Photovoltaic panels with a heat pump heat the pool in summer and serve the house in winter; the costs page prices that route and shows what it saves compared with the alternatives.

Do the cover first, whichever you choose

A cover stops the heat leaving in the first place, and US Department of Energy guidance credits covers with saving 50% to 70% of pool heating costs. A few mats on a covered pool do more than many mats on an open one, which is why the covers and efficiency page comes before any kit or system. The worked running-cost example shows the order of spending on a modelled 8×4m pool.

Sources and how the numbers were built

• Low Energy Supermarket, pool heating kit (viewed 20 October 2026): one to three 0.66m×6m mats with pump and 20W or 30W panel, £121.99–£309.99, VAT status not stated; the 3–5°C per day and 20°C to almost 36°C claims are the manufacturer's.
• B&Q, two-mat kit with pump and 20W panel, £230.99 at the time we looked.
• SPATA, swimming pool heating factsheet: solar collector area usually exceeds 50% of the pool surface. US Department of Energy (EERE, 2007) gives 50% to 100%.
• European Commission (CORDIS), EEC solar pool heating project, eight English pools, 1982–84: about 0.5m² of collector per m² of water; about 300kWh per m² of collector per outdoor season; efficiency 20–50%.
• Ofgem, price cap 1 October to 31 December 2026: gas 7.97p/kWh (5% VAT), electricity 26.32p/kWh.
• HMRC, VAT Notice 708/6: zero rate for installation in residential accommodation; a supply without installation is standard-rated.
• US Department of Energy, Better Buildings, Pool Efficiency: covers can save about 50–70% of pool heating costs.
• Our assumptions: 8×4m pool, 32m² of surface; boiler efficiency 85%; the 1982–84 collector yield applied to modern mats; kit area 3.96m² per mat (0.66m × 6m).

Questions people ask

Do DIY solar pool heaters work in the UK?

They add some heat on sunny days, but we found no independent UK figure for temperature gain. The best independent measurement is a monitoring project on eight English pools run in 1982–84, which recorded about 300kWh per square metre of collector over an outdoor season. The kit makers' 3–5°C-a-day claims come with no stated conditions.

How many solar mats do I need for my pool?

The trade body SPATA says collector area usually exceeds half the pool surface. An 8×4m pool has 32m² of surface, so about 16m² of collector, or four or five 0.66m×6m mats. The kits we found stop at three mats.

Is a DIY solar pool kit VAT-free?

No. A kit supplied without installation is standard-rated under HMRC VAT Notice 708/6; the zero rate applies to the installation of energy-saving materials in residential accommodation, and polypropylene pool mats are not named in the notice.