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The boiling point is the temperature at which a liquid transitions to vapor at a given pressure. Adding Ethylene glycol to water raises the boiling point above 212 °F (100 °C). This effect is called boiling point elevation. The boiling point also rises with system pressure; at 2 ATM a 30% V/V solution boils at approximately 262 °F (128 °C), compared to 217 °F (103 °C) at 1 ATM.
Operating above the boiling point causes vapor formation, which leads to cavitation in pumps, vapor lock in heat exchangers, and loss of system pressure control. In pressurized closed-loop HVAC and process cooling systems, the actual system pressure sets the effective boiling point of the glycol solution. This is why higher-pressure systems can operate at higher temperatures without boiling. This chart provides the maximum safe operating temperature at each concentration and pressure combination.
Note: Boiling points are calculated via Raoult's Law with Antoine equation vapor pressures for water and ethylene glycol. Valid for 0–100% V/V at 1–6 ATM.