Swimming pool heating cost

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What does it cost to heat a swimming pool?

There is no simple answer to this question there are numerous variables that it is not possible to give the best response so I will try to explain why it is so not easy to work out the cost of heating a swimming pool and make a comparison of the different methods of pool heating.swimming- exercise

First thing is to know how much heat you need to put in to your swimming pool to heat it up and therefore work out the cost. There are units of measurement for how many kilowatts (kw) of energy it takes to raise the temperature of fixed volume of swimming pool water.

Here is an example:
Say a 8,000 litre pool will need about 150 kilowatts of energy to raise the temperature of heat exchangerwater (from the tap) from 10°C to 25°C (pool water).

So if your electricity tariff was say set at 8p per kw/hr (Kilowatts per hour) then it will cost £12.00 (150(kw’s) X. 0.08p (pence) = 12 (£’s)

150 x 0.08 = 12

However with this example, the assumption is the swimming pool water looses no heat at all. Actually the swimming pool water loses heat not only while you are heating the water but as soon as the heater gets the water to the required temperature it begins to lose the heat and the heater has to work constantly to replenish that lost heat. There are countless ways a swimming pool can lose heat and the speed at which it loses heat depends on several factors:

Oil heaterSwimming pools can lose heat through the pool walls. The largest quantity of heat is lost from the pools surface area through evaporation and convection. The wind speed over your pool can have a huge affect on heat loss as well

Colder air temperatures cools the pool water. A swimming pool kept at very high temperatures will lose heat at twice the speed of a swimming pool held at lower temperatures against a background (ambient) temperature of say 20°C. So, the higher the temperatures are the quicker the heat loss. You can cut the cost of heating by turning the temperature on the pool heater thermostat down.

A pool without a cover loses more heat than a pool with one. A heat retention cover will cut down on heat loss. A solar cover on a good day will actually warm the water through solar gainHeat loss

On the point of heat loss through air movement across the pool a pool dome or enclosure can have a large influence on heat loss and big savings on the cost of heating a pool

The ambient air temperature at which the heat pump uses to heat the swimming pool can fluctuate day by day, season to season.

The amount of sunshine needed to warm the solar panels to heat the pool water also fluctuates season to season

In simple terms, you are really trying to heat a volume of water that is exposed to the elements, (wind cold etc) so the heating of a swimming pool is about “replacing the heat” that the pool water loses.replaced-liner-2
A heater’s thermostat senses when your pool water temperature drops by a degree (1°C) and the thermostat switches the heating on until the desired temperature that you’ve set the pool water is reached.
Assume your pool temperature drops by 1 degree centigrade every night and by the morning your heater has to get the pool water back up to the temperature that you’ve set at for the heating the pool water to stay at that level until the evening and then overnight it drops 1 degree C again.
An approximation at best scenario but it’s a simply illustration. Let us assume the swimming season is from May to say September, roughly about 135 days.

This table below shows

  • The volume of water in a swimming pool
  • The pools size
  • How much heat input in kilowatts is (kw) needed every day
  • And the amount of heat (kw) required for the season (as above assuming approx 135 days for a season)
Water Volume (approx) Pool size Heat needed per day (kw) Heat required for every season (kw)
8,000 litres (1,760 Gals) 12ft Round 9.3 1256
16,000 litres (3,520 Gals) 15ft Round 18.6 2512
25,000 litres (5,450 Gals) 18ft Round 29.1 3925
40,000 litres (8,800 Gals) 12 x 24ft 46.5 6280
64,000 litres (14,100 Gals) 15 x 30ft 74.4 10048
100,000 litres (21,990 Gals) 20 x 40ft 116 15700

These are approximate figures of the amount of heat you will have to put in to your swimming pool.
The figures above are based on a 1°C loss in temperature per day.
On colder nights it may be more heat loss, on warmer days it may be less.Maintaining a swimming pool

The table below show a list of  how much individual heating systems use in kilowatts  and the possible cost (depending on your tariff for electricity, and fluctuations in heating oil & gas prices) to put in different amounts of heat using diverse types of heater. The costs are based on assumptions shown below the table.

KW required Oil Gas Electric Heat Pump
1,200 £67 £39 £119 £28
2,500 £140 £81 £249 £59
4,000 £224 £129 £398 £94
6,000 £336 £194 £597 £141
10,000 £560 £324 £995 £235
15,000 £840 £485 £1,493 £353

Cost assumptions.

(Remember these costs are an example and do not reflect the current costs of fuel)

This is an example below to give you an idea

Electricity…..………… 9.00p per kw/hr heater efficiency 92% cost per kw output 9.78p

Gas………..…………….. 2.75p per kw/hr heater efficiency 85% cost per kw output 3.24p

Oil @ 45p per litre = 4.02 p per kw/hr heater efficiency 75% cost per kw output 5.6p

Heat pump…………… 0.09p per kw/hr heater efficiency 400% cost per kw output 2.25p

Air source heat pumpAir Source Heat Pumps operate with a Co-Efficient of Performance (COP) of 3 to 1, meaning that for every kilowatt of electricity you pay for, you get 3 kilowatts of heat back out. This is at least 3 times cheaper than a standard electric pool heater.

The outcome is:

Electric pool heaterFor small pools up to about 15ft round the lower purchase cost of standard electric pool heater is fine. However if your swimming pool size is bigger than the 15ft size then this choice using a standard electric pool heater is not so economical.

In the long term a heat pump purchased and used for heating your swimming pool over 5 years, the extra cost of the initial investment should be paid back with in lower fuel costs.

Solar heating:

Solar pool heatingThe cost of solar heating panels and how efficient they are much depends on the UK weather, and what seems in the last few years like we are experiencing shorter summers (2013 being an exception although we did have a very cold spring), and how much warm sunshine we gain. If the UK was situated near Spain or North Africa then one could say it is a good idea to have, but our climate is very changeable to say the least, so as yet the jury is still our regarding solar heating.

Remember this is just a guide to give you an idea how to find out the cost to heat a swimming pool. Your actual tariffs may vary depending on which energy supplier you use

John Cox TnISPE(Cert)

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