This is how I made a really cheap solar pool heater, and it works! It is a simple coiled hose attached to a wood frame and placed on the hot concrete. The pump is for a pond and moves 900 gallons per hour. The hose is 3/4″ and about 200 foot long. It will heat the water about 5 degrees above the ambient pool temperature on a partly cloudy day. The pool is large, so this setup is smaller than I should use. As is, it barely compensates for the temperature loss at night. I plan on adding a lot more hose and making a nicer permanent setup.
Post time: Jun-22-2017