UltraHeat Tankk s prevent the contents of your holding s from freezing solid when the temperature is sub-zero! Cold room and field tested third party Labs, some RV Manufactures themselves, and everyday RVer’s to protect down to -11 Degree Fahrenheit (-24 Degree Celsius ) on totally exposed RV holding s, lower with some additional modifications and insulation. The UltraHeat brand is the Original Holding Tankk to the RV Industry, the "Standard" to use 1991, it’s been copied but never beaten in performance and longevity.