In most heat transfer applications ethylene glycol-based fluids are your best choice because of their superior heat transfer efficiency. This efficiency is largely due to the lower viscosity of ethylene glycol solutions. Another benefit of this viscosity advantage is lower power consumption for re-circulation pumps and a lower minimum operating temperature
Propylene glycols are most commonly used in applications in which low acute oral toxicity is required, or for freeze protection where incidental contact with drinking water is possible. In some areas, use of propylene glycols is required by local regulation. Propylene glycol-based fluids are used extensively in food processing applications, but ethylene glycol-based fluids can also be used in some instances