What Is the Difference in Boiler and Automotive Anti-Freezes?

Background

• Both boilers and automobile radiators depend on circulating water to function. If the water inside those systems freezes, the boiler or radiator would no longer work. Adding an anti-freeze to the water ensures the systems continue working even if temperatures drop to the freezing point. Moreover, because water expands when it freezes, it could damage the system by causing the radiator or boiler to crack. Then the damaged system would not hold water, and it could not work even after temperatures rose above the freezing point again.

Basic Difference

• Automotive and boiler anti-freezes contain different chemicals. Automobile anti-freeze contains ethylene glycol while boiler antifreeze contains propylene glycol. The basic difference involves safety. Ethylene glycol is acutely poisonous if accidentally ingested orally. The United States Environmental Protection Agency classifies ethylene glycol as a toxic chemical. That means automotive anti-freeze requires more cautious handling, particularly when disposing of the used product.

Automotive Anti-Freeze

• Another difference involves function. Automotive anti-freeze contains silicates. The silicates tend to gel in the anti-freeze. That means automotive anti-freeze would not transfer heat as efficiently as boiler anti-freeze would, which makes it less desirable for use in boilers. However, that same characteristic means that automobile anti-freeze protects radiators from overheating during the summer.

Boiler Anti-Freeze

• Boiler anti-freeze contains propylene glycol. It transfers heat better than ethylene glycol does, which is desirable in a boiler. Moreover, the EPA does not categorize propylene glycol as a "hazardous substance," which makes handling and disposal easier. In addition, although propylene glycol is not suitable for human consumption in large amounts, the Federal Drug Administration classifies it as safe. That means less potential for danger to humans or animals if there is a leak with boiler anti-freeze than there would be with automotive anti-freeze.