Do I Need to Use Glycol?

July 7, 2021

Most Hydronic Heating Systems Use Water, So What is Glycol Used for in HVAC?

There are many propylene glycol uses in the world, but is it necessary to add glycol to water in hydronic heating systems? What about adding glycol for cooling systems? This article explains why adding glycol to water provides important protections.

Water is the Basic Fluid used in Hydronic Heating and Cooling Systems

Water glycol

Many building heating and cooling systems use water to move temperatures around the building. The water is heated or cooled, and pumps transport the water to the various coils where air takes the heat or cooling into the space.

To maintain good indoor air quality, fresh air must be brought into the building while some air is exhausted. The air is pulled in by fans located in air handling units and is the same temperature as the outdoor air. In northern climates, the incoming air temperature can be very cold. Care is exercised during the design to assure that the ice-cold air does not freeze the water but things can go wrong.

Three Example Systems Where Adding Glycol Can Save the Day

Example #1: Air Handling Unit Freeze Protection

Air Handling Unit Freeze Protection

Look at the photo above. This heating coil uses a two-way control valve with the main heating pumps operating on variable speed drives. This will save energy and operating costs.

Freeze Damaged Coils

The downside of the system is the concern about stopping the flow through the coil where cold air is rushing in. Engineers use a piping practice named primary-secondary to assure there is always flow across the coils. The primary-secondary piping depends on a small circulator pump to move the water around.

If the circulator pump fails, the flow may stop, and cold air could freeze the water and damage the coils. Many engineers will use a percentage propylene glycol antifreeze mixed with the water to avoid catastrophic coil damage.

Example #2: Glycol Chillers not used in the Winter

Many HVAC systems have air cooled chillers used throughout the summer. In the winter they are drained so they do not freeze. This provides two problems for owners.

What happens when we get a hot spell in the fall. The people in the building are hot and they do not blame the system, they blame the operations people. Adding glycol to cooling systems will allow the use in both summer and winter.

The second problem occurs when the cooling system is started. Many owners simply open the valves to the air cooled chiller and allow the system and the makeup water to fill the pipe. This causes a large amount of air to be introduced into the system. This air will cause cooling problems for weeks or even months.

When people ask, what is a glycol chiller? The answer could simply be a chiller that can run all year if needed. Remember that not any old antifreeze will do. The glycol used in chilled water systems should be the right percentage and have the right mix of inhibitors. Try our glycol concentration calculator to determine the required concentration for your application or contact us today for help finding the correct solution for your application.

Example #3: Pipe in Unheated Spaces

We showed above the glycol chiller can be used all year round. There is another concern with piping systems where there is no flow at times. Often these pipes may run through unheated spaces or spaces with cold outside air blowing across the pipe.

Sometimes the design included heat in a space to protect the chilled water or heating system. During the life of the building the space becomes unused. To save money, the owner may turn the heat down or even off. Water may freeze but a glycol antifreeze system will protect the pipe.

Additional Advantage of Glycol in Closed Hydronic Heating and Cooling Systems

Example of Corrosion

Not all glycols are the same. The Dowfrost® and Dowtherm® products supplied by Go Glycol Pros include an inhibitor package which protects the pipe much better than water or even water with chemicals added. Click here to learn more about the benefits of inhibited heat transfer fluid.

Adding the proper type, concentration (or mix), and brand of glycol to closed heating and cooling systems will offer protection. Glycols and antifreeze should not be added to systems without an understanding of the effects on pumps and heat or cool output. For assistance in getting started, contact our customer service team today!


Norm Hall Headshot


Norm graduated from Wayne State University in Electrical Engineering. Over the past 40 years at RLD Norm has worked on design/engineering of systems, estimating, outside sales & management. Norm enjoys golf, playing with his grandkids, teaching eighth grade catechism classes, and volunteering at local food banks.

Go Glycol Pros LogoGo Glycol Pros is a distributor of DOW® heat transfer fluid for over 20 years. We sell glycol online with no accounts or order minimums required. Available in 275 gallon tote, 55 gallon drum or 5 gallon pail, high purity DOW antifreeze is premixed with deionized water (DI water) at our in-house facility and ships out within just one business day. Our inhibited glycols include: DOWFROST HD propylene glycol, DOWFROST food grade propylene glycol and DOWTHERM SR-1 ethylene glycol.

Explore more helpful tips and advice at Our knowledgeable glycol experts are ready to help you with your latest hydronic HVAC project.

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Disclaimer: Go Glycol Pros and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the- information comes from many years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions that result from this information. Please feel free to contact us if you do have any questions.