I'm finding this thread especially interesting because I'm considering adding a heater to extend our swim season. Here in northern Kentucky (just south of Cincinnati, OH) our frost date is May 10 so there is a possibility we can still get really low overnight temps through mid-May. We've been comparing heat pump vs propane. We heat our home with propane so already have that on the property to tie in to. Our kids get out of school the last week of May/1st of June and go back to school the last week of August. So that's our "summer" where we use the pool the most, but the water is still uncomfortably cold in early June! We're hoping we can get some weekends of swimming during the end of May/early June that aren't frigid! And also afternoons/weekends through September because it's still quite warm during the day. Using the same comparison calculators that 1Tara1 is using, we changed our initial gut instinct to use propane to getting a heat pump. But now I'm back on the fence again after reading this thread! Any further comments any of you can add would be much appreciated! Thanks in advance!