I would recommend a heat pump before a gas heater. I have had a heat pump heating my pool for the past 5 years and it has worked flawlessly. It will cost more initially than a natural gas or propane heater but over time you will recover that costs. Only downside is that when the weather is cool the heat pump takes much longer to heat the pool. We usually wait for a warm few days forcast by the weatherman and start heating the pool during the warmest part of the daytime (Usually 11:00 AM to 7:00 PM. Once the pool has heated up (It may take a few days) it's easy to keep it at the desired temperature. I don't spend more than $150 average for electric (main filter pump, cleaner booster pump, heater) during the summer. I keep the pool covered with a solar cover until the kids are home during the summer, then it's off unless we get some unseasonably cold weather.