One of the questions we get asked many times is how much will it cost to heat my swimming pool. We wish we had a simple answer that we could give out but we do not, there are so many variables that it is impossible to give a definitive answer so in this article we will give you a rough estimate and we will try explain why it is so difficult to work out the cost of heating a swimming pool. How much it costs also depends very much on what type of heater you have so we will make a comparison of the different methods of pool heating.
In principle it is easy to know how much heat you need to put in to your swimming pool to heat it up and therefore easy to work out the cost. We have units of measurement for how many kilowatthours (kwh) of energy it takes to raise the temperature of fixed volume of swimming pool water. For example a small 8,000 litre pool like a 12ft splasher pool will need about 150 kw of energy to raise the temperature from 10 deg C (tap water) to 25 deg C (swimming pool water). With electricity at 15p per kw/hr then it will cost £22.50. Simple. Well yes it is but this example assumes that the pool water does not lose any heat and never will. If only this were true!
In reality the swimming pool water will lose heat not only while you are heating it but as soon as the heater gets the water to the desired temperature it starts to lose heat and you have to constantly replace that lost heat. There are many ways a pool can lose heat and the rate at which it loses heat depends on many factors.
Heating a swimming pool is really all about replacing the heat that the pool has lost. No matter how much you do to insulate and shelter the pool there is always going to be big losses in heat. So lets have a stab at estimating the heat required to maintain your pool temperature. Most heaters have a thermostat and these typically detect when your pool drops by 1 deg C and switch them on and they stay on until the temperature is back to where you set it. Lets say your pool drops 1 deg C each night so in the morning your heater has to get it back up and it stays there until evening and then overnight it drops 1 deg C again. Lets assume a season from May to mid September of 135 days.
The table below shows how much heat input is required each day and for the season for various pool sizes.
|Pool Volume (litres)
||Heat req’d per day (kw)
||Heat req’d per season (kw)
||12 x 24ft
||15 x 30ft
||20 x 40ft
Hopefully from this table you can get a rough idea of the total heat you will have to put in to your swimming pool. Remember though that the figures above are based on a 1 deg C loss per day. On colder nights it may be more on warmer days it may be less.
The table below lists how much it would cost to put in various amounts of heat using different types of heater. Cost assumptions are shown underneath.
Cost assumptions Electricity – 15p per kw/hr heater efficiency 92% cost per kw output 16.3p
Gas – 4.5p kw/hr heater efficiency 85% cost per kw output 5.3p
Oil – 70p per litre = 6.6 p per kw/hr heater efficiency 75% cost per kw output 8.8p
Heat pump - 15p per kw/hr heater efficiency 400% cost per kw output 3.75p
For small pools up to about 15ft round the lower purchase cost of an electric heater makes it a good buy. But if your pool is any bigger then the electric option is less attractive. Taking the longer view, say 5 years of ownership, the extra purchase cost of a heat pump is more than paid back in lower fuel costs.