Air-to-water heat pumps for additional heating of swimming pools are very simple and economical with high efficiency, which comes from a fact that they are used in times when the outdoor air temperature is high, usually over 20°C. They are cheaper than regular air-to-water heat pumps, because they use already existing swimming pool installations and equipment, such as a swimming pool circulation pump. The installation of this type of pumps is very simple and does not require much installation work to integrate it into regular maintenance equipment of the pool. Due to all this, but especially due to the price and efficiency, these heat pumps are a very good solution for cheap additional heating of outdoor swimming pools and extending their seasonal use for 1-2 months before the season and 1-2 months after the end of the season. They do not occupy large space and do not distort the external appearance of the swimming pool complex, and therefore they are used in all situations where it is inappropriate to use a solar collector.