Anti-freeze fluids

The typical anti-freeze solution is a mixture of water and propylene glycol, but a water/ethylene glycol solution, silicon oil, hydrocarbon oil, or refrigerant could also be used. With the water/propylene glycol fluid the percent glycol should be 40% or less. A 40% solution begins to freeze at –11 °F; below that temperature, an ice slurry develops that does not readily freeze solid causing pipes to burst. A glycol solution greater than 50% is not recommended due to a higher viscosity and lower heat capacity. Systems using glycol should be aware that it has a greater tendency to seep through piping joints than water and thus the piping system should be sealed with care and checked for leaks at scheduled intervals. Glycol is not compatible with zinc so galvanized pipes should not be used.

The use of automatic water makeup to heat transfer fluids selected to be an anti-freeze should be avoided. This is because the water makeup will dilute the anti-freeze mixture and making the fluid more likely to freeze when exposed to cold outdoor temperatures. The anti-freeze fluid should be periodically checked to assure proper performance.