We have a "Heat Siphon" heat pump from US Thermoamp. My impression is that gas heaters are great for getting the pool up to temp in a reasonably quick time (and are preferred by weekenders for that reason) while heat pumps are more economical when it comes to maintaining temperature (possibly better for people who use their pools frequently). It's mostly good for starting the pool up earlier in the spring, when the water is cold, but the air is getting warm. In the fall, it's a nice idea, but we've found that the air just tends to feel awfully chilly going into September (we live in Connecticut). Other than that, we started using a solar cover (and a GLI "whirlwind" reel), and found that the heat pump doesn't run much during the summer. (We've had the pool up to 90 degrees from the solar cover and at that point it's *almost* not even refreshing.) So far, we've had it in for 5 seasons (with a SWG) and have only had a minor part failure on it. They're not cheap, though - you'd probably be looking at $3500-4000 for a model big enough for a 30' pool.