Reliable, highly efficient and economical to run, heat pumps extract heat from the air (similar to a reverse cycle air conditioner), and use that heat to produce hot water.
Compared to gas and electric, heat pumps use just a fraction of the energy to generate the same amount of heat. Although initially heat pumps take longer than gas heaters to warm up the pool or spa water, they are much more economical and will then maintain the heating as well as gas heaters.
Benefits of heat pumps include their high energy efficiency and lower running costs. As a guide, you can save up to 80% over LPG and 50% over natural gas fuelled heaters. And the best thing about heat pump pool heaters is that they operate regardless of the weather.
One of the disadvantages of this type of system is that they can lose their high energy efficiency slightly once the weather really cools down, as the pump has to work harder to heat the water against the outside temperature. However, unless you live in an area that does experience very low winter temperature, this is not a concern
Another thing to consider is they can be expensive to initially install, but the low running costs will make up for this in no time at all.