I'm in Apex. I have a heat pump for my 20k inground salt water pool. I think the decision between a heat pump and gas heater depends on how you use your pool. If you only swim on the weekend, then a gas heater will work just fine. My wife swims laps every morning for exercise so we want to maintain the temperature instead of repeated heating and cooling cycles. The heat pump is efficient at doing this. For me, the season starts sometime mid to late April until early to mid October. One year I kept it open until Veteran's Day (November 11) which was a mistake because the pool got filled with leaves. I keep a solar cover installed until about mid June and then put it back on around mid September. As far as electricity bill increase, I can't say how much to attribute to the heater. At the same time, the bill is increasing due to the heat pump, it is also increasing due to the pool pump and 2 HVAC systems on my house. It is hard to separate the three contributions to the bill.
