From http://little-giant.com/pool_heating.html" (The section entitled "Little Giant® Sizing For Swimming Pools General Requirements" about halfway down the page) "Using these standards, the thermal conductivity is 7 BTU/Hr. Sq. Ft./°F or 140 BTU/Hr. Sq. Ft. 20°F difference. " Is this "BTU/Hr. Sq. Ft." a unit of heat loss? Do they mean per square foot? or perhaps x the square footage? My pool has 550 square feet of surface. I want to figure out the temp. drop per mph of wind, per degree of difference in air/water temp. per hour. And I guess you have to factor in the volume of the pool too, though they don't. A 10 ft deep pool would suffer less temp drop than a similar-sized 4 ft deep pool.