Heat & Insulate Your Outdoor Inground Pool

I. Insulating a UK Swimming Pool

Air source Heat Pumps:

If you read all this page you will see that Air Source Heat Pumps are the only realistic way to heat an outdoor swimming pool on a sustainable basis.

Covers and insulation help but the primary heat source is all important.

Gas and electric heaters are at most 80% efficient whereas the efficiency of an Air Source Heat Pump varies between about 450% to 1500% !!

Ground Source Heat Pumps are also very efficient but they cost at least 6x what an Air Source Heat Pumps costs. For details on the range that Bluepools provide, please click here.

We can deliver them immediately and so if you need one send an email or text to 07557 966459 and we will get if off to you straightaway - they have a built in Wifi controller and so the water temperature can be set from anywhere at any time.

Prices are as follows:

There are many cheap heat air surce heat pumps available on the Internet. Most of these will have worthless guarantees and are very likely to fail before the end of the first seasons use.

The heat pumps above are provided with a 3 year general guarantee and 10 years on the heat exchanger and compressor!!

Heat Loss from a Swimming Pool:

Swimming pool heat is lost from the water surface, walls and floor.

Heat loss is at a maximimum when the pool is in use and the summer cover has been removed. Most of this occurs because of the large amount of heat energy that is taken out of the swimming pool water when evaporation occurs from the pool's surface.

The evaporation rate is dependent on the pool’s initial temperature, the surrounding air temperature and humidity, and the wind speed at the pool surface. The higher the pool temperature and wind speed and the lower the humidity, the greater the evaporation rate. Though a windbreak— such as trees, shrubs, or a fence—can reduce evaporation, it may shade the pool from the sun, which is a strong natural heat source for the pool.

But if the pool is only used for 4 hours a day for 5 days a week on average then this major heat loss from the pool surface will only occur for about 12% of the time. If the pool is covered with a solar cover then most of the heat loss then occurs through the walls and floor of a conventional swimming pool.

Factors that affect the Heat Loss:

Heat lost through the walls and floor only occurs during the period when the pool is being heated up. This is becuase when the temperature gradient is continuous between the warm water in the pool and the point in the surrounding soil where the temperature is not being raised, heat loss will stop. The only thing that can remove more heat from the pool walls and floor is ground water flow in the soil.

It is sometimes necessary to provide land drains around the pool to stop ground water flow as otherwise it can be difficult to get the pool up to the desired temperature.

How to reduce Heat loss:

Covering a pool in-between periods of use is the single most effective means of reducing pool heating costs. As much as 90% of heat loss from a swimming pool is caused by evaporation. A pool cover acts as a vapor barrier that dramatically cuts heat losses from evaporation, resulting in significantly higher pool water temperatures. A high performance solar cover can reduce the water loss by evaporation by as much as 95%.

What are the different types of summer pool covers?

Pool covers are designed using UV-stabilized polyethylene, polypropylene, or vinyl to resist deterioration. A cover lasts several years.

Solar covers are reminiscent of bubble packing material, but using a thicker grade of plastic with UV inhibitors. If you want to turn your pool into a giant solar heater this is the type we recommend.

Vinyl covers consist of a heavier material and have a longer life expectancy than bubble covers. Insulated vinyl covers are also available with a thin layer of flexible insulation sandwiched between two layers of vinyl.

pool summer cover types

Solar Swimming Pool Covers

Solar covers heat a swimming pool by converting the sun's light into heat like thousands of tiny greenhouses, instead of reflecting it as water normally does. This heat energy is efficiently conducted into the pool water by the increased area of the covers underneath surface. Tests have shown that 6°C of free heat can be gained and the swimming season extended by a number of weeks!

In addition to significant energy savings, solar pool covers do the following:

The high heat absorption covers look this:

summer cover detail photo

The aluminium surface that projects down into the water maximises the contact area available to transmit the heat from the sun into the water and the aluminium colour reflects the light and heat coming up from the pool water back down into it.

Is it possible to add heating to an existing pool?

If you have a pool without heating and would like to extend your pool swimming season by 2 to 3 months each year then it is easy to add a pool heating system.

II. The Pool Heating Options

Available Options:

The options for pool heating include solar, heat exchanger using an existing oil or gas boiler, direct electric heating, heat pump using the ambient air as a heat sink, heat pump using the ground as a heat sink and finally a heat pump using ground water as a heat sink.

Selection Criteria:

The criteria that are most important in terms of assessing the relative merit of pool heating systems are the following with the most important ones first:-

  1. Reliability: It is no good having a pool where the temperature varies wildly from week to week - you just end up not using it.
  2. Running cost : If the heating is going to increase your energy bill by several hundred per cent - you will end up turning it off.
  3. Maintenance cost: This goes hand in hand with reliability - if the heating system is always leaking water you will end turning it off.
  4. Capital cost


Solar is very unreliable and if the system quality is not absolutely first class it can soon become very costly and irksome to maintain. After a few years of frost even the best system will start to leak - and emptying the system in winter does not really help because there will always be back-falling areas in the pipework that you cannot drain down. If you want to take advantage of solar power it is better to insulate the pool walls and floor and install a high performance energy absorbing summer cover all as described above.

Heat Exchangers & Direct Electric Heaters:

Heat exchangers and direct electric heaters will only cost about 30% of the cost of a heat pump but can use 10 x as much electricity or fuel costs. They are very reliable and cheap to maintain but can cost as much as 12 - 15 euros per day to run.

Heat Pumps Using Air As A Heat Sink:

Heat pumps of this type will use about a pound a day in power - depending on pool size and water temperature. They are very reliable and should last at least 5 - 7 years before requiring renewal and all the parts are replaceable. THEY ARE ONLY SUSTAINABLE WAY TO HEAT THE WATER IN AN OUTDOOR SWIMMING POOL.

Other types of heat pump:

Other types of heat pump will be economical to run but much more expensive to install and so we are not considering them further at this point in time.