Gas Pool Heaters: Gas heaters use either natural gas or propane to heat your pool water. They heat the water up fairly quickly. Depending on the outside air temperature and the pool water starting temperature, they can heat the water up 1 to 2 degrees per hour, on average. While gas heaters usually have a lower upfront cost, the cost of the gas to run the heater usually exceeds the cost of running a heat pump.
Pros: Lower upfront cost, heats water up fast, works in any outdoor temperature.
Cons: Higher cost to run
Electric Heat Pumps: They are powered by electric and use the ambient air surrounding the unit to heat your pool water. These electric heaters have much lower costs to run than the gas heaters. Since they use the air around the unit it will take a much longer time to heat the pool water and typically will not work below 55 degrees.
Pros: Lower run cost, Energy efficient
Cons: Higher upfront cost, slower temperature rise, does not work effectively below 55 degrees.