Works great to warm above ground pool Our pool is 18 feet round 4 feet deep and we use 6 mats. Started with 2 to see how well they worked and added 4 more. We do run them on their own small pump with hosing to avoid over using our integrated pool pump. As our pump is stronger we have put them flat on our balcony overhang as we don’t get full sun in the yard all day. Instructions say don’t put on roof but we use with separate pump so it seems to works on the roof. They need full sun to work best but they do produce very warm water when the sun is out. On cloudy days pool is 23-24 degrees c. But on sunny days the pool heats to 27 + depending on outside temp. We keep a 14mil solar blanket on when not in use.