A Heat Pump uses electricity to operate. They are actually a form of solar heater, as the sun-warmed air contributes to the efficiency of these units. This heat is extracted from the air, upgraded with a compressor, and then transferred to the water. Gas Heaters use natural or propane fuel. The gas is burned in a combustion chamber where the heat is transferred to the pool water.
Operation requires a storage tank for propane gas, or hookup to natural gas, where available.
The size and cost of a pool heater depends on the size of your pool and the conditions at your location. A range of costs are outlined above, plus the cost for a typical 15' x 30' Kidney Pool with a screen enclosure in central Florida. The higher the BTU, the more heat output. The average output is 900 to 1000 BTU's. To determine the best value, divide the total cost by the total SqFt of panel.