The Thermo-Pond pays for itself in as little as 2 months.Thermo-Pond floats on top of the water and is thermostatically controlled to never get hot. Unlike some other heaters, Thermo-Pond will never burn a pond liner or plastic pond. It naturally allows the pond to ice over while maintaining a hole through the ice. The hole in the top of the Thermo-Pond helps allow toxic gasses to escape all winter long. Allowing that gas exchange can help keep a healthier environment during the winter months Thermo-Pond should be used in ponds that are deep enough to allow plenty of livable water under the iced portion of the pond. Thermo-Pond has been tested in the Northwoods of Wisconsin at temperatures dipping down past 30 below Zero Fahrenheit. UL and CUL listed.