Glycol is an organic antifreeze and heat transfer fluid used in hydronic systems to lower freezing points and raise boiling points beyond water capabilities. Propylene glycol and ethylene glycol solutions, typically 20-50 percent concentration, protect systems in freezing climates and high-temperature applications. Glycol-based systems require special consideration for component compatibility and maintenance.
Performance Properties
Pure water freezes at 32 degrees Fahrenheit; 30 percent glycol solution freezes at negative 15 degrees Fahrenheit. Boiling points increase to 320+ degrees Fahrenheit in pressurized systems. Glycol reduces heat transfer efficiency by 8-15 percent compared to water, requiring larger heat exchangers and more aggressive circulator sizing. Higher viscosity at cold temperatures demands larger pipe diameters.
System Implications
Glycol systems require compatible expansion tanks with special bladders designed for glycol absorption resistance. Circulator motors and seals must be rated for glycol service. Annual fluid testing monitors pH levels and inhibitor depletion, with fluid replacement every 5-10 years. Glycol disposal requires special handling and professional fluid recycling services.