Pool heating calculator
Pool heating capacity in kW from the heat losses: evaporation to ASHRAE or VDI 2089, ΤΟΤΕΕ 20701-3 climate and heat-pump output. No account needed.
Heat losses, monthly load and required capacity — with an evaporation, convection and radiation breakdown.
Pool heating calculator — method and FAQ
How a pool’s losses are calculated
Heat leaves a pool by four routes: evaporation, convection, radiation and make-up water, with the sun credited as a gain. Evaporation is almost always the largest term and the only one a cover controls.
Evaporation is calculated with the ASHRAE Carrier equation, or to VDI 2089 for indoor pools. Each month is calculated separately over day and night periods, using the climate data of the ΤΟΤΕΕ 20701-3 station — temperature, humidity, wind and solar radiation.
The unit’s binding month
A pool heat pump is not judged on the average but on the month that presses it hardest — and that differs from machine to machine, because output falls as the air cools. Every size proposed is printed with its own binding month and with the air and water temperatures of that month. Every result carries the pair of temperatures it was calculated at — outdoor air temperature and water temperature. The nominal output at 7 °C with 35 °C water that is printed in the brochures is a different quantity, and does not compare with it.
The cover is valued by running the whole season twice — with and without — rather than by a fixed percentage: in Athens a bubble sheet on for 14 hours a day cuts about 64 % of the cost over the default season.
What it does not do
It does not calculate losses to the ground through the shell — measured studies put them near 2 % of the annual energy, and a term that small would imply a precision the rest of the model does not have. It is declared as an omission rather than hidden.
Frequently asked questions
How many kW does heating a pool need?
It depends on the surface area, the location, the target temperature, the exposure to wind and whether there is a cover — not on the cubic metres alone. As an indication, an open 32 m² pool in Athens at 27 °C from April to October asks for roughly 7 kW in its worst period; with an insulating cover both the load and the cost fall sharply.
Is a pool cover worth it?
Yes, and it is the cheapest kW you will ever buy: evaporation is the largest route of loss and a cover restricts it sharply for the hours it is on. In the Athens calculation, with an insulating cover on for 14 hours a day, the saving over the season comes to around 64 % of the running cost. The tool credits the cover with evaporation only — not with the convection and radiation it also restricts, for which no published figures exist — so the real benefit is larger than the calculation shows.
Why is a larger pump needed in April than in July?
In July the sun heats the pool for nothing and the air is close to the water temperature. In April and October the water wants the same degrees with colder air, more evaporation and less sun — that is where the size of the unit is decided, not in high summer.
Related tools
- Heat pump sizing for a dwelling — Heat loss, cooling load and required capacity — always with the operating conditions stated, so quotations become comparable.
- Climate data for Greek locations — Design temperatures, degree days and monthly climate data to ΤΟΤΕΕ 20701-3, for 62 ΕΜΥ stations — with a two-location comparison.