It may depend on the length of your pool season (which months are the pool opened), your desired temperature, whether you will be using a solar cover over your pool or not, and how many hours per day your pump is operating?
I manufacture the AquaCal Heat Pumps, the oldest and largest pool heat pump manufacturer in the World. So naturally I would say your only choice would be the SuperQuite Heat Wave!
OK, back to being a neutral respondent, you should look for several features:
- COP (Coefficiency Of Operation) which is a measurement of efficiency. Minimum standards under cold weather conditions (50 degrees) is 4.0 COP. At 80 degrees, COP should be in the 6.0+ range, for efficient systems.
- Heat Exchanger Design and Material. Most manufacturers are using Titanium, which is virtually impervious to chemical attack. Therefore, most offer a longer warranty on the heat exchanger, or lifetime, as in my case
- Sound Characteristics. Imagine where your heat pump may be located. If its going to be close to your house, expecially close to a bedroom or window, heat pumps are generally noisy, like an air conditioning unit. Some are Extremely quite, as in my case. ; )
- BTU Output. The questions I asked will determine how many BTU's will be needed to reach your desired temperature.
- Warranty, Service, and Support. How long is warranty coverage...and when you do have an issue, who handles the service call?