During the winter, gasses from decomposing matter and fish waste build up under the ice and can kill the fish if they are not allowed to escape. The PDT15 prevents this by keeping a hole open in the ice allowing fresh oxygen to enter. The PDT15 incorporates multiple temperature sensors to monitor water temperature as well as protect against over-temperature conditions. The sturdy, finned aluminum base spreads out the heat, running cooler to the touch while outputting maximum amount of heat into the water. In shallow ponds, the PDT15 can easily convert to a floating de-icer by simply removing the cover and float and turning the unit upside down to rest on its sturdy feet. UL Listed.