Heat pumps are without question the most efficient way to heat a swimming pool. They suck heat out the air and put it in your swimming pool at up to 600% efficiency.

But they have their limitations and they are particuarly noticable in the spring. This article was written on 19th April 2010. Yesterday the temperature reached 21.4C at about 4pm, perfect weather for your heat pump you might think. Well, yes, but at 6am that morning the temperature was 3.0C. It bearly got above 4.5C all night. That is cold! Too cold for a heat pump.  If it does not will freeze up and wait to defrost then it will be working at a COP of about 2 or 3 so the biggest and best heat pumps like the Nirvana M40 will only put about 8 or 12 kw in the pool.

Cold temperatures are a double whammy for pool owners. Not only will your heat pump struggle but the poor old pool which may be at 20 or 25C by now will only have a sheet of plastic between it and air at 3C or 4C for hours on end. Even with the heat pump on all night the pool will still be colder in the morning than it was the night before.

So if your heat pump is not making much head way in April or early May do not be surprised.  The rule of thumb for best heat pump performance at night is “would you go out in a short sleeved shirt?” By this we mean if the night is warm enough that you could wander around in short sleeves for a while without feeling cold then your heat pump will be fine. If you feel chilly in short sleeves or would not contemplate going out there without a jumper on then your heat pump will not like it much either.

If your heat pump has reverse cycle defrost you can forget most of the above. They will work down to lower temperatures but even at the lower temperatures you still only get 2 to 3 as a COP but since they are mostly used on indoor pools they don’t have the cold air temperatures next to the pool to deal with and should cope easily enough.

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