💧 Required Glycol Percentage
📈 Capacity Derating
Sizing Breakdown
Full Calculation Table
| Component | Basis | Value | Result |
|---|
How to Use the Glycol System Calculator
Choose propylene glycol for most commercial applications, or ethylene glycol for closed industrial process loops with no risk of human contact.
Enter the lowest temperature the fluid must resist freezing at, with a safety margin below your city's coldest winter design temperature.
Enter the flow rate, heat transfer capacity, and pump head loss the system was originally sized for using pure water.
Click Calculate Glycol System to see required glycol percentage, derated capacity, adjusted flow rate needed to recover capacity, and increased pump head.
Understanding Glycol Freeze Protection Systems
Glycol solutions protect hydronic systems from freeze damage when piping runs through unheated spaces, rooftop equipment, or outdoor locations exposed to Canadian winter temperatures. Adding glycol lowers the fluid's freeze point, but it also changes the fluid's thermal and flow properties in ways that affect system performance, which is why glycol systems need their own sizing consideration rather than simply swapping fluids in a water-based design.
| Propylene Glycol % | Approx. Freeze Point | Typical Application |
|---|---|---|
| 20% | -9°C | Mild climate freeze protection margin |
| 30% | -15°C | Vancouver, coastal BC |
| 40% | -23°C | Toronto, Montreal, Calgary |
| 50% | -35°C | Edmonton, Winnipeg, northern climates |
Values are general approximations for propylene glycol. Ethylene glycol freeze points differ slightly at the same concentration. Confirm exact freeze point against the specific manufacturer's published glycol concentration chart.
Choosing Propylene vs. Ethylene Glycol
Propylene glycol is the standard choice for most commercial HVAC applications because of its significantly lower toxicity, which matters anywhere the fluid could contact food processing equipment, evaluated under material standards like NSF/ANSI 51, potable water systems, or occupied spaces through a leak. Ethylene glycol offers marginally better heat transfer and lower viscosity at the same concentration, but its higher toxicity generally restricts it to closed industrial process loops where human contact risk is minimal and tightly controlled.
Why Glycol Reduces System Capacity
Glycol solutions carry less heat per unit volume than pure water and flow less easily due to higher viscosity, both of which reduce heat transfer effectiveness at a given flow rate through coils and heat exchangers, with the added friction loss worth checking against the pressure drop calculator for the specific piping involved. A system originally sized around pure water performance will lose some capacity once glycol is added unless flow rate is increased to compensate, which in turn increases pump head and pump energy. This calculator estimates that capacity loss and the flow rate adjustment needed to recover it.
Pump Head and Energy Impact
Higher glycol concentration increases fluid viscosity, which raises friction loss through piping, fittings, and heat exchangers at any given flow rate. Pumps selected for a water-based design may need to be re-evaluated once glycol is added, a check worth running through the pump head calculator, especially at higher concentrations needed for the coldest Canadian climates. Confirm actual pump curve performance against the glycol-adjusted head requirement rather than assuming the original water-based pump selection still applies.
Where Glycol Loops Commonly Appear
Rooftop-mounted chillers and condenser water loops exposed to outdoor temperatures are the most common Canadian commercial application, alongside dry coolers, closed-circuit cooling towers in freeze-risk locations, and process cooling loops serving data center or industrial equipment, a category the ASHRAE Handbook, HVAC Systems and Equipment volume covers alongside other secondary coolant system design. Pair this calculator with the chiller plant calculator to confirm the water-based flow and capacity values you are starting from before applying glycol derating.
Frequently Asked Questions
The required glycol percentage depends on how cold the fluid needs to resist freezing. A 30 percent propylene glycol solution protects to roughly minus 15 degrees Celsius, while a 40 to 50 percent solution protects to minus 23 to minus 35 degrees Celsius, covering most Canadian winter design temperatures. Always add a safety margin below the coldest expected outdoor design temperature, since exact freeze points vary slightly by manufacturer formulation.
Propylene glycol is less toxic and is the standard choice for most commercial HVAC applications, especially anywhere the fluid could contact food, potable water, or occupied spaces. Ethylene glycol offers slightly better heat transfer and lower viscosity at a given concentration but is significantly more toxic, so it is generally reserved for closed industrial process loops with no risk of human contact.
Glycol solutions have higher viscosity and slightly lower specific heat than pure water, which reduces heat transfer effectiveness at a given flow rate and increases friction loss through pipes, coils, and heat exchangers. A system originally sized for pure water will lose some heat transfer capacity and see higher pump head once glycol is added, unless the flow rate and pump are adjusted to compensate.
Standard commercial HVAC piping materials generally work fine with glycol solutions, but gasket, seal, and elastomer materials in pumps, valves, and expansion tanks should be confirmed as glycol-compatible, since some standard water-system elastomers degrade faster in glycol service. ACR copper tubing is used for the refrigerant side of the system rather than the glycol loop itself, which typically uses standard black steel or copper piping.
Related HVAC Tools
Water-based flow and capacity source
Condenser water side of the plant
Cold weather free cooling loop
Secondary loop freeze protection
Common process cooling application
Coil capacity before glycol derating
City-specific winter design temps
Process cooling glycol applications