Glycol Correction Factor Calculator

Correct GPM, pump head, and pipe sizing for ethylene or propylene glycol systems. Includes freeze point, fluid properties, and GPM adjustment.

🥶 Glycol System Inputs

CHW typically 44°F; brine or ice storage lower
GPM sized for pure water

📊 Glycol Correction Results

—
Corrected GPM (glycol)
—
Flow Correction Factor (Cf)
—
Freeze Point (°F)
—
Head Loss Multiplier
Fluid Properties at Operating Temp
Specific Gravity—
Specific Heat (BTU/lb·°F)—
Viscosity (cSt)—
Heat Capacity Factor (GPM×500×Cf)—
How to use: Multiply your water-based GPM by Cf to get glycol GPM. Apply the head loss multiplier to your pump head. Re-select pipe size using glycol GPM and the increased head loss.

📚 Glycol Selection Guide

ApplicationGlycol TypeTypical ConcentrationWhy
CHW plant, no freeze concernEG or PG20–25%Minimum needed; lower viscosity penalty
CHW + outdoor pipingEG30–35%Protection to ~0°F design temp
Ice storage / low tempEG30–40%25°F leaving temperature
Food/bev, indirect contactPG30–40%GRAS (food safe)
Extreme cold climateEG40–50%Protection to −30°F
Never exceed—50%Higher conc. hurts heat transfer significantly
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About This Calculator

This glycol correction calculator adjusts a water-based hydronic design for ethylene or propylene glycol antifreeze. Pick the glycol type and concentration and enter your water-based GPM; the tool returns the corrected glycol flow, the flow correction factor Cf, the freeze point, and a head-loss multiplier, along with specific gravity, specific heat, and viscosity at the operating temperature.

Glycol carries less heat per gallon and flows with more friction than water, so a glycol loop needs higher flow and more pump head for the same duty. Use the corrected GPM and the head-loss multiplier to re-check pipe size and pump selection, and use the freeze point to confirm protection for your coldest piping.

Formula & Method

Flow correctionCf = 1 ÷ (SG × Cp)
Glycol flowGPMglycol = GPMwater × Cf
Head-loss mult.HLmult ≈ 1 + 0.008 · (ν − 1)
Heat capacity500 × SG × Cp  (BTU/hr per GPM·°F)

Because heat carried ≈ GPM × 500 × SG × Cp × ΔT, holding duty constant means GPMglycol = GPMwater ÷ (SG · Cp); the constant 500 = 8.33 lb/gal × 60 min/hr for water. The head-loss multiplier approximates the higher friction of viscous glycol from kinematic viscosity ν (cSt). Property values for specific gravity, specific heat, viscosity, and freeze point are approximate ethylene and propylene glycol corrections per standard hydronic practice (ASHRAE Fundamentals glycol data); always confirm against the fluid manufacturer's tables for final design.

Frequently Asked Questions

Why does a glycol system need more GPM than water?
Glycol carries less heat per gallon than water because the product of its specific gravity and specific heat is lower than water's. To move the same BTU per hour you need more flow. The flow correction factor is Cf = 1 divided by (SG times Cp), and corrected GPM equals the water-based GPM times Cf. A typical 30 percent glycol mix raises required flow by roughly 5 to 10 percent.
How much does glycol increase pump head and pressure drop?
Glycol is more viscous than water, which raises friction loss in the piping. This tool estimates a head loss multiplier of about 1 plus 0.008 times (viscosity in centistokes minus 1), so a 30 percent mix near 4 to 7 cSt adds roughly a few percent, and high concentrations at low temperature can add considerably more. Apply the multiplier to your water-based pump head and re-check pipe sizing with the corrected GPM.
Should I use ethylene or propylene glycol?
Ethylene glycol has better heat transfer and lower viscosity, so it is preferred where toxicity is not a concern, such as sealed CHW or outdoor piping. Propylene glycol is food-safe (GRAS) and used near potable or food and beverage systems, but it is more viscous and carries a larger flow and pump-head penalty. Both protect against freezing; this tool shows the freeze point for each by concentration.
What glycol concentration should I use?
Use the lowest concentration that protects against your design low temperature, typically 20 to 35 percent for most chilled water systems and 30 to 50 percent for cold climates or low-temperature loops. Avoid exceeding 50 percent because higher concentrations sharply hurt heat transfer and raise viscosity. Match the freeze point to your coldest expected piping temperature with a margin.

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Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.