TES Thermal Energy Fluid is a hydronic heat transfer fluid. It is a mixture of propylene glycol, de-ionized water and corrosion inhibitors. It is used to prevent freeze damage to the TES system if it shuts down in freezing conditions and to provide corrosion protection for the heater components. TES Thermal Energy Fluid is used in every TES unit, all hoses and TEX Thermal Exchangers. The freezing point of TES Thermal Fluid is thirty degrees below zero Fahrenheit (-30 F). TES Thermal Energy Fluid is non-toxic. No VOC's. No hazardous ingredients. Exclusive for use with TES to protect machine and maintain warranty.