I'm in northern NJ and have had a heatpump for 10 years. Its an 85,000 btu unit and my pool is a 20 x 40 inground - works great. Whatever you do make sure to use a solar cover on the pool at night and when not in use - it makes a huge difference. Two years ago I added a pair of 2' by 20' solar panels that just lay on the ground by the fense. They handle all the heating of the pool from late may till mid august. The heat pump is only needed to bring the pool up to temp (like I did two weeks ago) and to provide some extra heat during april and early may and mid august till I close in late sept.