How to Use a Refractometer to Test Glycol Concentration

March 9, 2020

A hydronic heating or cooling system is one of the most efficient types of systems when it comes to providing comfort for a building. Thanks to the serviceability of the major components, a building owner can maintain their system for optimal efficiency and system life.

When servicing hydronic equipment, we often take the following steps:

  1. The equipment is isolated
  2. System fluid drained
  3. Maintenance performed
  4. Glycol fluid is replaced

What happens to glycol in HVAC systems? Once the fluid is replaced, the glycol solution may be diluted to a concentration lower than design. A system with overly diluted glycol leads to undesired performance, a reduction of corrosion inhibitors, and (for colder climates) a reduction in freeze/burst protection. Correcting glycol concentration is easy using on-site heat transfer fluid testing.

Refractometer Test 

We recommend testing your heat transfer solution concentration whenever the system has been serviced using an easy, on-site fluid analysis tool such as a refractometer.  Refractometers measure the glycol concentration and gives the antifreeze freezing point. This instrument requires only a few drops of fluid for glycol testing and requires no adjustment for fluid temperature.

The below video demonstrates how to test your system using a refractometer.

Please find below the Freezing and Boiling Points chart used in our how-to video for both DOWFROST and DOWFROST HD Propylene glycol and DOWTHERM SR-1 Ethylene Glycol.

Propylene Glycol Freezing and Boiling Point Chart (DOWFROST and DOWFROST HD)

Propylene Glycol Freezing Point and Boiling Point Chart

Ethylene Glycol Freezing and Boiling Point Chart (DOWTHERM SR-1)

Ethylene Glycol Freezing Point and Boiling Point Chart

Upon completing your glycol testing, you may need to increase your system's concentration using glycol addition. Our concentration correction calculator makes it easy to determine how much glycol is needed (100% concentrated) to bring your solution back to the required levels. See our glycols available for purchase online here.

Need additional help? Contact us today.

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.

View Dow Ethylene Glycol, Propylene Glycol and Food Grade Propylene Glycol

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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.