• Heat pumps are used in houses and swimming pools. The pumps use a refrigerant gas to transfer heat from the air to the pool. The gas has a high heat transfer capability, and is compressed to concentrate the heat it absorbs and pass it into the water before the gas is cooled again. Heat pumps are known for their energy efficiency, but they do have several problems when they are used to heat pools.
  
  

Water Temperatures

• Heat pumps do not produce their own heat, they only transfer it (most have electric elements in case of emergencies, but these should be used as little as possible). This means that the amount of heat a heat pump can produce depends in part on the air temperature. The size of the pool is also a factor. A small heat pump cannot heat a large pool effectively, and heat pumps are not as dependable for maintaining high temperatures.
  
  

Climate Changes

• Heat pumps can only work when the air is warm enough for the refrigerant to absorb heat. If the temperature drops below 50 degrees Fahrenheit, the heat pump will start losing efficiency and will eventually switch over to the electric element, which uses a large amount of energy and negates any savings the heat pump would have produced. This makes the heat pump difficult to use in colder climates and winters.
  
  

Initial Costs

• Heat pumps are one of the most expensive heating options to buy and install, despite their savings later on. Pool owners may not be able to afford these high upfront costs.
  
  

Maintenance

• Heat pumps are one of the most complex heating devices and must be installed by a professional, adding to the initial costs. Homeowners do not have the tools and experience necessary to diagnose heat pumps for problems or fix issues themselves, so if the heat pump stops working the repair fees may be higher than more simple heating systems that homeowners can repair themselves.