Universal Propylene & Ethylene Glycol Calculator for HVAC & Hydronic Systems

Yes. This calculator utilizes standard industry specific gravity and volume formulas compatible with most inhibited Propylene and Ethylene glycol fluids. However, always verify specific requirements with your manufacturer's technical data sheet (TDS).

The Concentration Adjustment section is designed to match the way techs actually test systems:

• System Volume (Gal): The total gallons in the loop, either calculated in Section 1 or known from drawings.
• Source Glycol %: The strength printed on the drum or tote (for example, 95% concentrate or 55% blend).
• Current % (Testing): The actual concentration in the system now, measured with a refractometer.
• Target % (Desired): The concentration you want to end up with, based on required freeze protection.

Take a clean sample of system fluid and place it on the refractometer lens. Read the glycol percentage according to the instrument’s scale for either Propylene or Ethylene glycol. Then:

• Select the correct Fluid Type (Propylene or Ethylene) in the Refractometer Check section.
• Enter the percentage reading into the Refractometer Reading (%) field.
• The calculator will estimate Freeze Point, Burst Point, and Boiling Point based on standard reference data.

This same reading can be entered as the Current % (Testing) in the Concentration Adjustment section to determine how much to drain and refill.

Vapco strongly advises against concentrations below 25%. While glycol can provide freeze protection at lower levels, concentrations below 25-30% lose their bacteriostatic properties. This allows biological growth (bacteria, algae, and slime) to flourish, which can clog pumps and foul heat exchangers. If a system must run at 20%, a professional biocide monitoring and injection system is mandatory. For standard maintenance-free operation, keep concentrations above 25%.

Freeze Protection ensures the fluid remains completely liquid at the lowest expected temperature, allowing pumps to operate. Burst Protection involves a lower concentration that allows the fluid to turn into a "slush" but prevents it from expanding and damaging pipes or components.

Use Propylene Glycol for systems with potential potable water contact, food processing (NSF HT-1), or residential applications where low toxicity is required. Use Ethylene Glycol for industrial efficiency and heavy-duty cooling where toxicity is not a concern, as it offers superior heat transfer.

Utilize the Concentration Adjustment section of this tool. By entering your Total System Volume, your Current Test Percentage (via refractometer), and your Desired Target Percentage, the tool will provide the exact amount of fluid to drain and replace with either water or glycol concentrate.

The Safety Factor % in Section 1 is there to account for unknowns: extra piping, coils, and components that weren’t measured exactly. A default of 10% is typical for most jobs. For systems with large heat exchangers, multiple risers, or where drawings are incomplete, counter staff or contractors may choose a slightly higher factor to avoid under-filling.

The Capacity Margin (Safety) multiplies the entered BTU/hr load to account for real-world conditions, future expansion, and unknowns. A value of 1.15 (15% margin) is common. Using higher margins (up to 2.0) may be appropriate for very critical loads or uncertain designs, but always coordinate with the system engineer or manufacturer recommendations.

The flow and tonnage calculations use standard HVAC formulas (BTU/hr = GPM × factor × ΔT and 12,000 BTU/hr per ton). The factor is adjusted for glycol type and approximate concentration. This provides a practical engineering estimate for sizing discussions, but it should not replace a full heat load design. Always confirm final equipment selection with a licensed engineer or the OEM’s design tools.

Inside sales and counter staff can use the calculator as a guided script. Ask the contractor:

• “What kind of glycol is in the system now—Propylene or Ethylene?”
• “What percentage did your refractometer just read?”
• “What percentage do you want to target for your lowest ambient?”
• “About how many feet of each pipe size do you have?”
• “Do you have any expansion or buffer tanks, and what are their gallon ratings?”
• “Do you know the system BTU load and design ΔT?” (if they want flow/tonnage guidance)

With these answers, the counter person can walk through each section on-screen and print or email a complete summary for the contractor.