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What is the greenest way to heat your swimming pool

With the onset of global warming many people are looking at their energy consumption and wondering how they can cut down in their carbon emissions. So with that in mind we undertook a study of the greenest way to heat a swimming pool.

The 5 main ways to heat your pool are by conventional gas boiler, condensing gas boiler, oil boiler, heat pump or direct electric.

The biggest problem in discussing heating a pool is to know just how much heat you need. In fact this is such an impossible question to answer we have side stepped it and instead looked at how much CO2 is emitted for a fixed heat output. Over the course of a 5 month season you might typically put 12,000 kw of heat in to a swimming pool so we are using that as our basis.

Input or Output

First lets understand the difference between heat input and heat output. You put IN your “fuel” in to your heater, the heater “burns” it and gives OUT a certain amount of heat to your water. What you put in is never the same as you get out, some of the energy in the “fuel” is lost and how much is lost depends on the efficiency of your heater. For example a conventional gas boiler is typically 85% efficient so 15% of the heat the gas produces is lost and does not go in the water. On the other hand a heat pump is typically 400% efficient so each unit of energy put in becomes 4 units out putted to the water.

Therms, BTUs, Kilowatts, Kilo what?

Understanding the units that are used for measuring heat is very confusing. We are going to use kilowatts. The reason for this is because energy companies quote their prices in kilowatt hours, which is a kilo watt of energy supplied for one hour. Electric heaters are rated in kw but most boilers are rated in BTUs (British Thermal Units). 1 kw is 3,412 BTU. So a 125,000 BTU rated gas boiler uses 36.6 kw as input energy, but at 85% efficient the output is 31 kw.CO2 emissions

The table below shows the amount of input energy required to give an output to the water of 12,000 kw and cost impact on your bank balance and to the atmosphere.

Heater Input (KW) Cost (£) CO2 Emission (tonnes)
Conventional Gas 14,100 £388 2.68
Condensing Gas 12,370 £340 2.35
Oil 16,000 £451 4.00
Heat Pump 3,000 £283 1.29
Direct Electric 12,120 £1,142 5.19

It is clear that the heat pump comes out on top due to its 400% efficiency.

The following prices were used based on those available in February 2007.Gas – 2.75 pence per kw/hOil – 30p per litre equating to 2.82 pence per kw/hElectricity – 9.42 pence per kw/h

The CO2 emissions are from the Environment Watch website.

If you use cheaper night time rate electricity you can greatly reduce your electricity costs but of course the carbon emissions are just the same.