In both HVAC and industrial cooling systems, efficiency often comes down to how well your heat transfer fluid performs under pressure, literally. A properly formulated glycol mixture isn’t just about preventing freezing; it directly affects how heat moves, how pumps work, and how long your system components last. Get the ratio wrong, and you may face higher energy use, reduced flow rates, or even long-term damage from corrosion or scale.

Whether you’re operating in desert heat or mountain cold, the goal is to protect equipment while maintaining optimal heat transfer performance. Glycol, commonly ethylene glycol or propylene glycol, when mixed correctly with water and the right additives, offers dependable protection and consistent thermal behavior across seasonal and load variations.

In this guide, we’ll break down the science and strategy behind glycol mixture optimization. We’ll also share insights from EAI’s decades of hands-on experience managing glycol water systems, and heat transfer fluids generally, across the Western U.S., helping facilities meet efficiency goals while reducing operational risks.

Understanding Glycol Types and Their Physical Properties

Glycol is a versatile heat transfer fluid used across HVAC, refrigeration, and industrial systems. But not all glycols are the same. Choosing the right one along with understanding its physical properties is key to building a safe, efficient, and long-lasting cooling system.

Mono Ethylene Glycol (MEG)

Also referred to as ethylene glycol, MEG is the most commonly used glycol in industrial applications. Ethylene glycol delivers excellent thermal performance with a low freezing point and high boiling point, making it ideal for low-temperature environments. However, it is toxic if ingested, so it’s generally reserved for systems with no risk of human exposure.

• Freezing point: ~ -36°C at 50% concentration
• Boiling point: ~ 197°C
• Thermal conductivity: Moderate
• Viscosity: Increases as temperature decreases

Mono ethylene glycol is derived from ethylene oxide, a petroleum-based raw material, and is widely used in chillers, heat exchangers, and hydronic loops.

Propylene Glycol (PG)

Propylene glycol is often used as a heat transfer fluid in HVAC systems where a non-toxic fluid is required—such as in food processing, breweries, or hospitals. While slightly less efficient in heat transfer compared to MEG, it’s recognized as a food additive and considered safe under most exposure scenarios.

• Freezing point: ~ -32°C at 50% concentration
• Boiling temperature: ~ 188°C
• Specific gravity: Slightly higher than water
• Colorless, miscible with water, and more environmentally friendly

PG’s slightly higher dynamic viscosity than MEG means systems may require higher pumping power, especially at lower temperatures.

Triethylene Glycol (TEG)

Triethylene glycol is less common in HVAC but widely used in natural gas dehydration and specialized industrial processes. It has a high boiling point and low volatility, making it useful in systems operating under extreme heat.

Each of these glycols shares hydroxyl groups that enable strong hydrogen bonding with water, making them highly miscible and easy to blend. Still, the differences in specific heat, thermal conductivity, and viscosity mean that selection impacts more than just freeze protection. It directly affects pump efficiency, heat exchanger sizing, and even maintenance intervals.

Key Properties Affecting Performance

Optimizing a glycol mixture isn’t just about adding the right percentage of antifreeze but also understanding how glycol changes the behavior of the entire system. The key performance factors are largely dictated by the mixture’s thermal conductivity, specific heat, viscosity, and impact on flow characteristics.

Freezing Point Depression and Boiling Point Elevation

The primary function of glycol in a water glycol solution is to lower the freezing temperature and raise the boiling point. The more glycol you add, the more the freezing point drops, but only to a point. Concentrations above 60% can actually reduce performance due to increased viscosity and reduced thermal transfer.

• A 50% ethylene glycol solution typically freezes around -36°C
• A 50% propylene glycol solution freezes closer to -32°C
• Boiling points rise well above 100°C, depending on system pressure

This ensures the fluid remains in a liquid state under both low and high operating temperatures.

Viscosity and Flow Resistance

As glycol concentration increases, so does the dynamic viscosity of the mixture. This means pumps must work harder to move the fluid, particularly at lower temperatures, where the fluid thickens.

• Higher viscosity = reduced flow = increased energy use
• Glycol-heavy fluids may require upgraded pumps, larger pipes, or higher pressure

Balancing concentration with flow capability is essential for maintaining overall system efficiency.

Specific Heat Capacity and Heat Transfer

Specific heat is a fluid’s ability to absorb heat without a large temperature rise. Water has a high heat capacity, making it extremely effective. Glycol has a lower heat capacity, so the more glycol you add, the less efficient your system becomes at moving heat.

For example:

• Water: ~4.18 kJ/kg·K
• 50% Ethylene Glycol: ~3.3 kJ/kg·K
• 50% Propylene Glycol: ~3.0 kJ/kg·K

This reduction impacts system sizing, especially in cooling towers, chillers, and heat exchangers.

Determining the Right Mixing Ratio

Getting the mixing ratio right is one of the most critical steps in optimizing a glycol mixture solution. Too little glycol, and the system is vulnerable to freezing damage. Too much, and you risk reduced heat transfer performance, elevated viscosity, and unnecessary cost.

Common Glycol-to-Water Ratios

• 30% Glycol / 70% Water: Provides freeze protection to around -15°C, ideal for mild climates or indoor HVAC systems.
• 40% Glycol / 60% Water: Suitable for moderate cold protection and improved burst resistance.
• 50% Glycol / 50% Water: Protects down to approximately -36°C (MEG) or -32°C (PG), common for outdoor or rooftop equipment.
• Above 60%: Rarely recommended; heat transfer efficiency drops significantly, and fluid becomes harder to circulate.

Adjusting for Climate and System Type

Ambient temperature, system exposure, and equipment sensitivity all influence your ideal glycol mixture. A chiller in Arizona may need less freeze protection but better heat efficiency, while rooftop systems in Colorado require a more robust solution to handle lower temperatures.

It’s also important to account for:

• Elevation and pressure (which affect boiling point)
• Equipment limitations (pump specs, heat exchanger design)
• Regional water quality and pretreatment compatibility

Tools like specific gravity charts or refractometers can help confirm the actual density in the field and ensure the fluid’s mass fraction is in spec. This not only protects your system but keeps performance at its peak throughout seasonal changes.

Compatibility and Common Additives

A glycol mixture isn’t just glycol and water. To perform reliably over time, especially in industrial or HVAC systems, it often includes additional additives that stabilize performance, prevent corrosion, and help identify leaks.

Corrosion Inhibitors

Because glycol can degrade into acidic byproducts over time (especially when exposed to oxygen or heat) corrosion inhibitors are critical. These additives protect system metals such as copper, brass, steel, and aluminum from chemical attack.

• Common inhibitors include silicates, phosphates, and nitrites
• Inhibitor concentration must be monitored over time to remain effective
• Inhibitor depletion leads to acidic fluid conditions and system damage

pH Buffers and Stabilizers

Glycol system volume should be slightly alkaline to avoid corrosion. Additives help maintain optimal pH, even as the glycol mixture ages or becomes contaminated.

• Target pH: 8.0–9.5 for ethylene or propylene glycol systems
• Below pH 7.0, the risk of metal loss increases significantly

Dyes and Leak Detection

Most commercial glycol formulations contain brightly colored dyes (pink, red, green, or blue) to help users quickly detect leaks in pipes, joints, and coils. These colorless base fluids become visible with the right dye and lighting.

• Dyes do not alter physical properties, but they improve maintenance visibility
• Especially helpful in large systems where leaks can occur slowly or unnoticed

Safety, Environmental, and Regulatory Considerations

While glycol mixtures offer critical system protection, they also introduce safety and environmental risks that facility operators need to manage responsibly. The type of glycol you use (ethylene glycol or propylene glycol alcohols) has a direct impact on how the fluid must be handled, stored, and disposed of.

Toxicity and Handling

• Ethylene glycol is toxic if ingested and can be harmful to both humans and animals. It has a sweet taste, which increases the risk of accidental consumption.
• Propylene glycol, on the other hand, is generally recognized as safe (GRAS) by the FDA when used as a food additive and is commonly used in food processing environments and healthcare facilities.

Regardless of type, both should be treated with care:

• Use appropriate personal protective equipment (PPE) during handling
• Store in labeled, sealed containers away from direct sunlight and incompatible materials like acids and strong oxidizers
• Avoid spills near storm drains, open soil, or ventilation points

Environmental Impact

If a glycol solution leaks into the environment, it can deplete oxygen in waterways and disrupt local ecosystems, just as any antifreeze-like liquid. Both ethylene glycol and propylene glycol are miscible in water, making them harder to contain once released.

• Clean spills immediately with absorbent materials
• Follow local and federal guidelines for chemical disposal and reporting
• Some jurisdictions regulate discharge thresholds for glycol-containing fluids in sanitary systems

Regulatory Compliance

Facilities using glycol must comply with OSHA hazard communication standards, EPA discharge rules, and local water district policies especially if they use glycol in cooling towers, chillers, or natural gas operations.

Proper documentation of material safety data sheets (MSDS), glycol concentration logs, and maintenance practices helps demonstrate compliance and protects against liability in case of an incident.

EAI’s Expertise in System Optimization

At EAI, we’ve spent more than 30 years helping facilities across the Western U.S. get the most out of their glycol systems. From rooftop chillers to mission-critical industrial cooling loops, we know that the right glycol mixture can make the difference between stable operation and expensive downtime.

Our team of water treatment engineers and field technicians specializes in:

• Selecting the ideal glycol type for each application, balancing freeze protection, efficiency, and safety
• Designing custom mixing ratios based on equipment design, geographic conditions, and system load
• Monitoring fluid performance over time to ensure proper viscosity, pH, and inhibitor levels
• Supporting HVAC systems with optimized water-glycol solutions that reduce scale, corrosion, and energy loss

We also help clients identify and capture rebates that apply to glycol-cooled equipment and associated cooling tower services. Whether it’s sub-metering, softener upgrades, or evaporative loss credits, our rebate matching program helps offset project costs while improving system efficiency.

Learn more about our cooling tower water treatment services.

For a deeper look at how glycol works in real-world applications, visit:

• What is Glycol and How is It Used in HVAC Systems?
• A Guide to Understanding Industrial Glycol Cooling Systems
• Free Ebook: The New Rules of Cooling Tower Water Efficiency

Precision Makes the Mixture

A properly formulated glycol mixture ensures your entire system operates with maximum thermal efficiency, reliability, and safety. By selecting the right glycol type, maintaining the proper mixing ratio, and monitoring performance factors like viscosity, pH, and specific heat, facilities can extend equipment life, reduce energy costs, and avoid unplanned shutdowns.

Whether you’re running a campus HVAC network, a food production facility, or a critical industrial process, the right glycol strategy is key to year-round performance.

Need help optimizing your glycol system?
EAI offers tailored solutions backed by decades of hands-on experience with glycol water, cooling systems, and heat transfer fluid management.
Talk to an expert today.