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Why is Glycol recommended in a Hydronic system?

Glycol, specifically propylene glycol or ethylene glycol, is often recommended in hydronic systems for its antifreeze and freeze-protection properties.

Glycol is added to the water in the hydronic close loop system, and the resulting mixture is known as “hydronic glycol” or “hydronic antifreeze.”

The percentage of glycol in a hydronic closed-loop system depends on various factors, including the desired level of freeze protection, the type of glycol used (propylene glycol or ethylene glycol), the lowest expected temperature, and the specific requirements of the system. Generally, glycol concentrations in hydronic systems typically range from about 10% to 50%.

Here’s why glycol is recommended in a hydronic system:

  • Freeze Protection: In colder climates, water within a hydronic system can freeze when temperatures drop, leading to potential damage to pipes, components, and the system as a whole.
  • Antifreeze Properties: Glycol also provides antifreeze protection, which is crucial in situations where the system may be exposed to sub-freezing temperatures. By preventing freezing, glycol helps maintain the functionality and integrity of the system during cold weather.
  • Corrosion Inhibition: Glycol-based solutions often contain corrosion inhibitors that help protect the various components of the hydronic system, such as pipes, pumps, and valves, from corroding over time.
  • Expansion and Thermal Stability: Glycol helps prevent excessive expansion of water due to temperature changes, reducing the risk of pressure buildup within the system.
    It’s important to note that while glycol offers these benefits, there are also some considerations to keep in mind:
    • Glycol Concentration: The glycol-to-water ratio is important. Too much glycol can reduce heat transfer efficiency, while too little may not provide sufficient freeze protection. The optimal concentration depends on the specific application and the lowest expected temperatures.
    • Maintenance: Glycol-based systems require periodic maintenance to monitor glycol concentration, pH levels, and overall system performance. Regular checks and adjustments are necessary to ensure proper functionality.


Messana recommends the use of propylene glycol due to its lower aggressiveness towards metal parts, higher environmental friendliness, and lower toxicity.

In summary, glycol is recommended in hydronic systems primarily for freeze protection, antifreeze properties, corrosion inhibition, and overall system stability. Proper design, installation, and maintenance are essential to ensure the glycol-based hydronic system operates efficiently and safely.
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