A Pool's Running Costs, Worked End to End

The baseline: where the money goes today

Our example pool holds 48,000 litres (8×4m, 1.5m deep, 32m² of surface). Uncovered, it loses heat steadily, and we assume the gas boiler supplies about 11,000kWh of heat across a May–September season — an assumption, because exposure, depth and use move it a lot (the trade body SPATA says an uncovered outdoor pool can lose as much as 90% of its heat through evaporation). At Ofgem's October to December 2026 gas price (7.97p/kWh including 5% VAT) and 85% boiler efficiency that is about £1,035, call it £1,040. The 1.1kW single-speed pump runs eight hours a day over the 153-day season: about 1,350kWh, £355 at the electricity cap of 26.32p. Call the baseline £1,390 a season, and note the heating share is the bigger and softer target.

Step one: the cover — £300 spent, ~£420/season saved

A bubble cover used overnight and on non-swimming days cuts total heat demand by roughly 40% in our example (a cautious assumption: US Department of Energy guidance credits covers with saving 50–70% of pool heating costs, and SPATA says up to 80% of surface heat loss). Heat demand falls from 11,000 to about 6,600kWh; the gas bill drops from about £1,035 to about £620. A £300 cover (a planning figure; get quotes) repays itself within a season on gas, which is why every page on this site refuses to size solar for an uncovered pool — full reasoning on the covers page.

Step two: the pump — £750 spent, ~£250/season saved

A variable-speed pump running longer hours at low speed filters the same water for a fraction of the energy (pump power falls with the cube of flow rate: one European datasheet shows 0.99kW at full speed and 0.07kW at 1,000rpm, and US research puts variable-speed savings at 50–90%; the pump-sizing sums follow). Seasonal pump consumption drops from 1,350kWh to roughly 400kWh: £355 becomes £105. Fitted cost £600–£900 as a planning figure; payback about three seasons, and the quieter plant room is free.

Step three: the heat pump — £4,800 spent, heating bill falls by almost half

Replace the gas boiler with an 11kW inverter pool heat pump. The covered pool's 6,600kWh of heat now arrives via a seasonal COP of 5 (a good inverter unit in mild weather: manufacturer datasheets rate 4.5–7.8 at 15°C air, while SPATA gives 3.5–4.5 as a typical outdoor-season average), consuming roughly 1,320kWh of electricity: £347 at the electricity cap, versus £620 of gas. That saves about £270 a season on its own, a long payback for £4,800 (the bottom of the Renewable Energy Hub's April 2026 installed range for a 12kW unit); the real purpose is converting heat demand into an electrical load that solar can serve. The cost-per-kWh comparison shows each heat source on the same prices. (Details of sizing and controls on the pairing page.)

Step four: the panels — £5,700 spent, the bill nearly vanishes

A 3.6kWp MCS-installed array (£5,740 at DESNZ's £1,595 per kW median for small installs; 0% VAT until March 2027 where it qualifies) generates about 3,500kWh a year in the East Midlands (PVGIS: 981kWh per kWp), about 2,000kWh of it between May and September. Pool electricity in the season is about 1,720kWh (heat pump 1,320 plus pump 400); we assume 60% of it comes straight from the array, a cautious figure that depends on timing the heating window to daylight. Residual grid purchases: 40% of 1,720kWh at 26.32p, about £180 a season. The other 2,500kWh or so a year goes to the house or the grid, worth about £300 if a quarter is used in the house at 26.32p and the rest exported at around 8p (export rates in October 2026 run from 2–6p on standalone tariffs to 16p where you also buy your electricity from the supplier).

The ledger, honestly totted

Total invested: about £11,550 across the four steps (£300 cover, £750 pump, £4,800 heat pump, £5,700 array). Seasonal pool running cost: £1,390 down to roughly £180 (residual grid purchases), saving about £1,210 a year — plus roughly £300 of off-season household value from the array. Simple payback on the whole programme: about 7.7 years (£11,550 divided by £1,510), or about 9.5 years on pool savings alone. The steps do not pay back equally: the cover in under a season, the pump in about three, but the heat pump replacing a working gas boiler only in about eighteen years (£4,800 divided by £270) unless it displaces direct electric heating or the panels are on the roof for the house too. The order still matters, and the programme survives being done gradually as budget allows, in exactly this order. Costs for every component sit on the costs page; differences for indoor pools (year-round demand changes the array sizing logic) are on the indoor vs outdoor page.

Sensitivities: at a seasonal COP of 4 the end-state running cost is about £215 rather than £180, and with only half the pool electricity coming straight from the array it is about £225. Your pool will differ — volume, exposure, season, region, and how warm your household actually likes the water all move these numbers. Send the specifics through the contact form and we will run this exact ledger on your pool, assumptions shown, and email you the result. Sources and assumptions are listed below.