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Glycol Freeze Protection Calculator

Required glycol concentration for freeze protection with performance penalties per ASHRAE Fundamentals Ch. 31 and Dow Chemical product data

Free glycol freeze protection calculator for HVAC technicians and hydronic system designers. Enter your target freeze protection temperature to find the required propylene or ethylene glycol concentration. See the full performance impact: specific heat reduction, viscosity increase, density change, and flow rate correction factor. Includes burst protection temperature , glycol slushes before it freezes solid, so burst protection is lower than the freeze point.

Pro Tip: Don't over-concentrate. 50% propylene glycol protects to -28°F but cuts your heat transfer by about 14% and makes the fluid 5 times thicker than water. Use the minimum concentration that gives you the protection you need, plus a small safety margin. In most of the northern US, 30-40% propylene glycol covers the realistic risk.

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Glycol Freeze Protection Calculator
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How It Works

  1. Select Glycol Type

    Choose propylene glycol (HVAC, potable water systems) or ethylene glycol (industrial only , toxic). Propylene glycol is used in virtually all HVAC and food-service applications.

  2. Choose Your Mode

    Use "Find concentration" to enter a target freeze temperature and get the required %, or use "Analyze concentration" to enter a known % and see all properties.

  3. Review Performance Penalties

    The calculator shows specific heat, density, viscosity multiplier, heat transfer derating, and flow rate correction. Use the flow correction to adjust your GPM , you need more flow to deliver the same BTU/hr with glycol.

Built For

  • HVAC contractors determining glycol concentration for outdoor hydronic piping in freeze-prone climates
  • Mechanical engineers specifying glycol for snow melt systems, outdoor unit heaters, and rooftop air handlers
  • Service technicians checking whether existing glycol concentration is adequate after a system dilution or top-off with water
  • Solar thermal installers specifying freeze protection for glycol-filled collector loops
  • Food processing facility engineers selecting propylene glycol concentration for potable-safe cooling systems

References

  • ASHRAE Handbook , Fundamentals, Chapter 31: Physical Properties of Secondary Coolants (Brines)
  • Dow Chemical , DOWFROST and DOWFROST HD Propylene Glycol Technical Data Sheets
  • Dow Chemical , DOWTHERM SR-1 Ethylene Glycol Technical Data Sheet
  • Dynalene , Glycol-Based Heat Transfer Fluids Engineering Guide

Frequently Asked Questions

Glycol solutions don't freeze solid like water , they form a slush first. The freeze point is where ice crystals begin to form. The burst protection point is much lower, where the slush becomes solid enough to potentially damage pipes. A 30% propylene glycol solution freezes at +5°F but provides burst protection down to -10°F. This is why glycol-filled systems survive power outages that would freeze and burst water-only piping.
Propylene glycol is non-toxic and FDA-approved for food contact. Ethylene glycol is toxic , a spill or leak into potable water could be dangerous. Ethylene glycol does provide slightly better freeze protection per percent and lower viscosity, so it's used in industrial-only applications where toxicity isn't a concern and performance matters more.
Glycol has a lower specific heat than water (it carries less heat per pound per degree). At 50% propylene glycol, specific heat drops to about 0.86 BTU/lb·°F compared to 1.00 for water. Combined with the slightly higher density, you need roughly 15-20% more GPM to deliver the same BTU/hr. The calculator shows the exact correction factor for your concentration.
Yes. Glycol breaks down with heat and oxygen exposure, forming organic acids that lower pH and can corrode system metals. Inhibited glycol products (like Dow DOWFROST HD) include corrosion inhibitors that deplete over time. Test glycol annually with a refractometer for concentration and pH strips for acidity. Replace or re-inhibit when pH drops below 7.0.
Disclaimer: Glycol property data is approximate and derived from published manufacturer data sheets. Actual properties vary by manufacturer, inhibitor package, and fluid age. Always verify with the specific glycol product's technical data sheet for critical applications.

Learn More

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Glycol Freeze Protection: Concentration, Performance, and Common Mistakes

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