Does antifreeze reduce the thermal efficiency of the system?

Introduction: Does the use of antifreeze really reduce system heat?

Yes — but not because of the antifreeze itself, but because of changes in the physical properties of the circulating fluid.

Antifreeze (usually based on ethylene or propylene glycol) lowers the freezing point of water, but at the same time:

• Reduces its Specific Heat Capacity.
• Increases its viscosity (thickness).
• Slightly lowers its Thermal Conductivity.

These changes naturally lead to a slight decrease in heat transfer efficiency — but this loss is predictable, manageable, and in many cases recoverable.

In this article, we will examine, in practical and understandable technical detail, how:

• How much does efficiency actually decrease?
• What factors exacerbate or reduce this loss?
• How can we minimize this effect by choosing the right antifreeze and adjusting the system?

Why do people think that antifreeze reduces the “heat of the system”?

Many users — especially in mountain villas — feel after filling the heating system with antifreeze:

• The radiators become “less hot”.
• The package works more but the ambient temperature does not rise.
• The gas or electricity consumption has increased.

This feeling is quite real — but the reason is not “bad antifreeze”, but the difference in thermophysical properties between pure water and glycol solution.

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Physical properties of antifreeze vs. water: what changes?

1. Specific Heat Capacity

• Pure water: ~4.18 kJ/kg·K
• 50% ethylene glycol solution: ~3.3 kJ/kg·K

→ ~21% reduction in the amount of heat that each kilogram of fluid can carry.

Practical result: To transfer the same amount of heat, the fluid must circulate at a higher flow rate — or have a higher inlet temperature.

2. Viscosity

• The opposite is thicker than water (especially at low temperatures).
• At 0°C, the viscosity of a 50% ethylene glycol solution is about 3 times that of water.

Practical result: The circulating pump has to do more work → Power consumption increases.

3. Thermal Conductivity

• Water: ~0.6 W/m·K
• 50% glycol solution: ~0.45 W/m·K

→ ~25% reduction in the ability to transfer heat from the pipe wall to the fluid.

Practical result: Heat transfer in the exchangers becomes slightly slower.

Structured Data:

Three main factors that reduce thermal efficiency with antifreeze:

1. Decreased specific heat capacity

2. Increased viscosity

3. Reduced thermal conductivity

How much does efficiency actually decrease? (Actual numbers)

Many people think "system heat is halved", but the reality is different:

Key point:

In most parts of Iran (even Alborz and Zagros), a concentration of 20–30% is sufficient to prevent freezing at temperatures down to -15°C.

In this range, the efficiency loss is less than 6% — which is practically imperceptible.

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What factors exacerbate this efficiency loss?

1. Using too much concentration

Many people think “the thicker, the better”. This common mistake causes:

• The fluid to become too thick.
• The pump cannot generate enough flow.
• The radiators to stay cold.

✅ Solution: Always adjust the concentration based on the minimum temperature in the area.

Example:

• Temperature -10 °C → 25% antifreeze
• Temperature -20 °C → 35% antifreeze

2. Using car antifreeze instead of industrial antifreeze

Car antifreeze:

• Contains phosphates and silicates.
• It creates deposits in heating systems.
• This deposit creates thermal insulation → Reduces efficiency by up to 30%!

✅ Solution: Use only phosphate-free industrial antifreeze in heating systems.

3. Failure to reset the system after adding antifreeze

Systems designed for pure water, as the fluid properties change, require adjustment:

• Increase pump speed (in smart systems)
• Increase the set temperature of the package
• Check system pressure

✅ Solution: Calibrate the system after filling with antifreeze.

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How to compensate for the loss of efficiency? (Practical solutions)

1. Use an optimized formulation of antifreeze

Some industrial antifreezes contain heat transfer additives that:

• Improve thermal conductivity.
• Reduce viscosity at low temperatures.

2. Increase circulation flow rate (in adjustable systems)

In systems equipped with a variable speed pump:

• Increase pump speed by 10–15%.
• This will compensate for the lack of heat capacity.

3. Increase water heater temperature

If your package regulates the outlet temperature:

• Increase the set temperature by 5–10°C.
• This will create a greater temperature difference for heat transfer.

4. Insulate pipes and radiators

By reducing heat losses along the path, the effect of reduced internal efficiency is neutralized.

✅Practical example:

A 150-meter villa in Damavand with 30% antifreeze:

• Before: Radiator temperature 65°C
• After: Radiator temperature 62°C
• After increasing the package temperature to 70°C: Radiator temperature 66°C
•  →The problem is completely solved.

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When does antifreeze increase efficiency?!

It is interesting to know that in some cases, antifreeze improves efficiency:

1: Preventing freezing and cracking of pipes

Freezing causes:

• Cracks in exchangers
• Leaks
• Permanent reduction in pressure and flow

Antifreeze prevents these damages → Maintaining long-term efficiency.

2: Reducing corrosion and deposits (in high-quality industrial antifreeze)

Industrial antifreezes contain corrosion inhibitors that:

• Prevent the formation of oxide layers on metals.
• They maintain constant heat transfer over time.

In contrast, systems filled with unprotected city water begin to scale and corrode after 2–3 years → efficiency reduction of up to 25%

Practical data:

Systems with industrial antifreeze have better efficiency after 5 years than systems with "unprotected pure water".

❓❓❓ Frequently Asked Questions (FAQ) ❓❓❓

❓ Can I add antifreeze only on cold nights?

No. Antifreeze should always be in the system. Adding it occasionally will cause uneven dilution and the formation of separate layers.

❓ Is propylene glycol antifreeze less efficient?

Slightly more than ethylene glycol (~2–3%), but the difference in practice is negligible. Its advantage is that it is non-toxic.

❓How do I know if my antifreeze is causing a decrease in efficiency?

• Measure the temperature of the radiators with a thermometer.
• Compare with the situation before antifreeze.
• If the decrease is more than 5°C, check the concentration or type of antifreeze.

❓Can I dilute antifreeze with demineralized water?

Yes — and it is recommended. Demineralized water prevents the formation of deposits and improves the performance of antifreeze.

Guide to choosing antifreeze concentration based on regional temperature

⚠️ Warning: Concentrations above 50% are not recommended — both in terms of efficiency and viscosity.

✍️  Conclusion: Antifreeze is not the enemy of efficiency

Efficiency loss with natural antifreeze is predictable and manageable. By choosing:

• the appropriate concentration based on the temperature of the area,
• high-quality industrial antifreeze (without phosphates and silicates),
• and resetting the system after filling,

you can prevent freezing without sacrificing your heating comfort for safety.

In fact, in the long term, industrial antifreeze keeps the system’s efficiency more stable by preventing corrosion and deposits — while unprotected systems deteriorate year after year.

If you need expert advice to identify the type of deposit or the optimal selection of chemicals, Abrizan Company’s specialists, with more than 20 years of experience in advanced laboratories, are ready to provide customized solutions to various industries.

☎️Free call and consultation with Abrizan specialists☎️