Check the listing for details. Solar Sun Rings Swimming Pool Heater Cover SSR-101 w/ Anchors (Choose Quantity). Condition: New. Listed at 92.96 USD. Solar Sun Rings® Blue Swimming Pool Heater Cover Blanket SSR-101 With Anchors (Choose Quantity) Our Solar Sun Rings® are passive solar swimming pool heating devices, constructed from two layers of U.V. resistant vinyl. The upper clear layer directs the suns rays onto the bottom blue layer which absorbs about 50% of the sunlight, converting it to heat. The remaining sunlight filters through the ring into your pool water. Each rings puts out 21,000 BTU of heat. The majority of heat loss from a pool comes from the water surface at night. Solar Sun Rings® do not cover the entire surface of your pool; therefore it allows heat to escape. To help keep the warm water in your pool at night we recommend you use additional insulation such as solar fish or a solar blanket. Each ring measures 60" inches in diameter. Do not over inflate. Do not use as a floatation device. How Many Rings Will I Need For My Pool? 12' Round Pool - 3 Rings 15' Round Pool - 5 Rings 18' Round Pool - 7 Rings 21' Round Pool - 10 Rings 24' Round Pool - 13 Rings 28' Round Pool - 17 Rings 12'x24' Oval Pool - 7 Rings 15'x30' Oval Pool - 13 Rings 18'x33' Oval Pool - 16 Rings 12'x24' Rectangle Pool - 8 Rings 14'x28' Rectangle Pool - 14 Rings 15'x30' Rectangle Pool - 15 Rings 16'x32' Rectangle Pool - 16 Rings 18'x36' Rectangle Pool - 19 Rings 20'x40' Rectangle Pool - 26 Rings Note: Solar Sun Rings® may vary in color and design from one manufacturing lot to the next. If you are purchasing additional rings to add to your existing rings they will be functionally the same, but may appear visually different. Coverage: Solar Sun Rings® are warrantied to be free of manufacturing defects for one year. Warranty is limited to materials and workmanship.