SYSTEM FILL CALCULATOR
Glycol & Distilled Water
Size the fill. Set the blend. Know how much to mix.
What this calculates
A fresh fill of an empty system. Tubing size and length determine volume; your selected target determines the blend percentage. Remaining water or old fluid will change the final blend. Quantities are estimates and exclude purge waste.
Choose the target for your system
The 35% starting value is an example, not a protection recommendation. Follow the glycol and boiler manufacturers’ limits, dilution instructions and temperature charts. Confirm the mixed concentration with the appropriate tester.
Calculation & product reference
System volume = tubing length × gallons per foot + other system fluid.
Glycol product = system volume × target glycol % ÷ product glycol %.
Added distilled water = system volume − glycol product.
Preset estimates: ½″ PEX = 0.0092 gal/ft; ⅝″ PEX = 0.014 gal/ft. Replace these with your tubing manufacturer’s stated capacity when available. All quantities are US gallons; 1 gallon = 128 US fluid ounces. Assumes additive volumes for planning.
Oatey: Cryo-Tek -100 product information lists 55% propylene glycol. Its mixing guide distinguishes product dilution from actual glycol concentration. Fernox Alphi-11 is available as 100% concentrate. Its option calculates the volume percentage of full-strength Alphi-11 product, not chemical glycol purity: Alphi-11 volume = total volume × target % ÷ 100. Other options are generic concentration inputs, not brand-specific specifications. Reference checked September 2026.