The Zurn Wilkins ZWFR Backflow Preventer Freeze Protection Device from Zurn Industries LLC monitors the water temperature within the valve. When the temperature-regulating thermostat senses water is nearing the freezing point, the valve opens, allowing warmer supply water to flow into the system. As the system reaches 40 F, the valve closes. The device is ideal for regions where occasional freeze/thaw cycles occur, yet winterization is not common.