Pool heating calculator
Most pool heat is lost from the surface by evaporation. A cover is worth more than any amount of heater capacity.
kW
per kWh
Time to heat
38:44:27
- Heat energy needed
- 465 kWh
- Electricity at that COP
- 93 kWh
- Cost to heat up
- 26.03
- Standing heat loss
- 6400
- Cost to hold the temperature per day
- 8.60
- Per month
- 261.81
- Heating hours
- 38.74
Show the working
- Pool volume = 40 000
- Surface area = 32
- Current temperature = 18
- Target temperature = 28
- Heater output = 12
- Heat pump COP = 5
- Electricity price = 0.28
- Cover in use = 0
- dt = 28 - 18 = 10
- Heat energy needed = 40 000 * 4.184 * 10 / 3600 = 464.889
- Heating hours = 12 > 0 ? 464.889 / 12 : 0 = 38.7407
- Time to heat = 38.7407 * 3600 = 139 467
- Electricity at that COP = 464.889 / 5 = 92.9778
- Cost to heat up = 92.9778 * 0.28 = 26.0338
- Standing heat loss = 32 * (0 > 0 ? 60 : 200) * max(10, 0) / 10 = 6400
- daily_loss_kwh = 6400 * 24 / 1000 = 153.6
- Cost to hold the temperature per day = 153.6 / 5 * 0.28 = 8.6016
- Per month = 8.6016 * 30.4375 = 261.811
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- energy = volume x 4.184 kJ per litre per kelvin x temperature rise
- surface loss is roughly 200 W per square metre per 10 K of temperature difference, or 60 with a cover
A cover cuts evaporative loss by 70% or more. It is the highest-return purchase in pool ownership.
Heat pumps lose capacity as the air cools, so a unit sized for summer will struggle in spring.