I live in Long Island and use a heat pump with a solar cover at night. The heat pump works very well even on the cooler nights and solar cover retains the heat at night. I just had the pool at 84 during the recent cold spell (50's at nigth) last week.

We have a heat pump in our fiberglass pool in NJ. Its a heat siphon 3.25. It has a great efficiency rating for generating heat with the elecricity that it uses. We have found it wonderful and very effective. When we got those 5 days of rain last week I turned off the heat pump since knew we would not swim with the rain and cool temps. Last Friday the air temp went up to 82 degrees. I ran the heat pump from 9am to 7pm and took the pool water from 71 degrees to 85. So on the weekend were were able to swim comfortably. Check out poolheatpumps.com. They have the best prices and will price match if you find it cheaper. Also very knowledgeable since that is what they specialize in. Lastly you can get an additional discount ($100? at www.troublefreepool.com if you sign up as a member for free..another great pool info site. Hope that helps.

Ls

We are also on Long Island and our experience has been similar to reeko's. (We have only had the pool for a few weeks so we are not experts yet)! We use a heat pump with an automatic cover and the water is always comfortable, even at night and during the colder days. Ours is an Aquacomfort Heat Pump, which is supposed to be very efficient and we have been very happy with it. I think you should check out lsbarkley's recommendation first because barkley found much better prices than we did. Also ours is a vinyl pool, not fiberglass like yours and barkley's, and I don't know whether that would make a difference.