Propylene Glycol Heat Transfer Fluid FREEZLIGHT® −20 °C for Heating Systems

Propylene glycol based heating fluid Freezlight -20°C application

FREEZLIGHT® −20 °C is a ready-to-use propylene glycol heat transfer fluid for indoor heating systems, radiators, hydronic underfloor heating, gas boilers, electric boilers, and solid-fuel boilers.

The crystallization onset temperature is −20 °C. The fluid is formulated with propylene glycol and demineralized water and contains a package of corrosion-inhibiting, stabilising, and antifoam additives. It contains no nitrites or amines.

FREEZLIGHT® −20 °C is recommended for systems in which pipelines, radiators, and heat exchangers are located inside the building and are not directly exposed to frost or wind. For outdoor sections, rooftop heat exchangers, solar thermal collectors, unheated rooms, or systems with an unknown amount of residual water, we recommend FREEZLIGHT® −32 °C with a greater low-temperature safety margin.

Key Specifications of FREEZLIGHT® −20 °C

What Is FREEZLIGHT® −20 °C

FREEZLIGHT® −20 °C is a ready-to-use non-freezing fluid designed to transfer heat and protect the system from damage during an emergency temperature drop.
Unlike water, the heat transfer fluid does not freeze immediately at 0 °C. As it cools to the specified temperature, crystals gradually begin to form. With further cooling, the amount of crystals increases, the fluid thickens, and its mobility decreases.
Therefore, the −20 °C rating indicates the temperature at the onset of crystallization. It is not the recommended continuous operating temperature and does not guarantee normal circulation at an ambient temperature of −20 °C.
For the system to remain operational, the temperature of its coldest section must stay above the crystallization onset temperature of the heat transfer fluid.

When FREEZLIGHT® −20 °C Is the Right Choice

FREEZLIGHT® −20 °C is recommended when:

• all pipelines are located inside the building;
• radiators and heat exchangers do not extend outdoors;
• there is no equipment installed on the roof or facade;
• pipelines do not pass through cold attics, canopies, or unheated rooms;
• the building is heated continuously or regularly;
• as much water as possible has been removed after flushing;
• the actual temperature of the coldest section of the system does not approach −20 °C;
• no additional safety margin is required for a prolonged emergency heating shutdown.

FREEZLIGHT® −20 °C is suitable for private homes, apartments with independent heating, offices, shops, workshops, administrative buildings, and production facilities where the entire heating system is located within the protected building envelope.

When We Recommend FREEZLIGHT® −32 °C

Choosing a heat transfer fluid only by the minimum temperature shown in the weather forecast is not correct. The design of the system and the operating conditions of its coldest component must also be considered. FREEZLIGHT® −32 °C propylene glycol heat transfer fluid is recommended when:

• part of the pipeline is located outside the building;
• a heat exchanger or cooling fins are installed on the roof;
• the system passes through an unheated attic or technical room;
• the equipment is exposed to strong wind;
• the building may remain without heating for a prolonged period;
• extended power outages are possible;
• the facility is used seasonally;
• a significant amount of water may remain in the system after flushing;
• the actual operating conditions cannot be predicted accurately;
• an additional low-temperature safety margin is required.

FREEZLIGHT® −32 °C is selected not because it is of higher quality than FREEZLIGHT® −20 °C, but because a particular system requires greater protection against cooling.

Practical Experience of Novohim

In one multi-storey building heating system, part of the heat-exchange equipment with cooling fins was installed on the roof.
During a period of frost, the air temperature was close to −20 °C. At the same time, there were strong winds, high humidity, and intensive cooling of the exposed heat-exchange surfaces.
The temperature on the roof and the actual operating conditions of the equipment differed from the general weather forecast for the city. Strong wind accelerated heat loss from exposed metal surfaces, especially after circulation was reduced or stopped.
In the coldest sections, the heat transfer fluid with a crystallization onset temperature of −20 °C began to crystallize and lost the mobility required for circulation.
The pipelines and heat exchangers remained intact, but normal circulation stopped and the heating system temporarily ceased to operate.
This case demonstrates that protecting pipes from mechanical damage and maintaining system operation are two different objectives. A fluid that has begun to crystallize may not rupture the equipment, but the circulation pump may no longer be able to move the thickened fluid containing crystals.
For this reason, Novohim recommends FREEZLIGHT® −32 °C for systems with outdoor heat exchangers, rooftop equipment, or exposed pipelines.

Residual Water Changes the Crystallization Temperature

FREEZLIGHT® −20 °C is supplied at a ready-to-use concentration and does not require dilution.
However, after flushing, pressure testing, or previous operation with water, some water may remain:

• in low sections of pipelines;
• in radiators;
• in heat exchangers;
• in underfloor heating circuits;
• in manifolds;
• in pumps;
• in horizontal pipe sections;
• in buffer tanks;
• in areas where complete drainage is not possible.

After the ready-to-use heat transfer fluid is filled into the system, the residual water mixes with it and reduces the propylene glycol concentration. As a result, the actual crystallization onset temperature becomes higher than the specified −20 °C.
For example, if the total system volume is 1,000 litres but 100 litres of water remain after flushing, only about 900 litres of ready-to-use heat transfer fluid can be added. The proportion of the finished product in the final mixture will be reduced by approximately 10%.
The new crystallization onset temperature cannot be determined by simply subtracting a number of degrees. The relationship between propylene glycol concentration and crystallization temperature is non-linear.
After filling the system, you should:

1. ensure full circulation and thorough mixing of the heat transfer fluid;
2. take a sample from the operating circuit;
3. check the concentration using a refractometer calibrated for aqueous propylene glycol solutions;
4. adjust the composition if necessary;
5. repeat the measurement after the fluid has been fully mixed.

If the approximate volume of residual water is unknown or the concentration cannot be measured, it is advisable to select FREEZLIGHT® −32 °C with a greater low-temperature safety margin.

Applications of FREEZLIGHT® −20 °C

The heat transfer fluid can be used in:

• indoor radiator heating systems;
• hydronic underfloor heating circuits;
• gas boilers;
• electric boilers with heating elements;
• solid-fuel and pellet boilers;
• independent heated towel rail circuits;
• indoor cooling systems;
• indoor process heat-transfer circuits.

Use is permitted provided that the manufacturer of the boiler, pump, heat exchanger, and other equipment allows aqueous propylene glycol heat transfer fluids.

Gas and Combination Boilers

In gas boilers, the product must be used in accordance with the equipment manufacturer’s requirements.
In a combination boiler, the heat transfer fluid must circulate only in the heating circuit. It must not enter the domestic or drinking water circuit.

Solid-Fuel Boilers

Use in systems with solid-fuel and pellet boilers is permitted only when properly designed overheating protection is installed.
Prolonged local overheating or boiling accelerates propylene glycol ageing, depletes the additive package, and shortens the service life of the heat transfer fluid.

Electrode Boilers

In electrode boilers, heating depends on the electrical conductivity of the working fluid.
FREEZLIGHT® −20 °C may be used in such equipment only with the boiler manufacturer’s explicit approval and after confirming compliance with the required electrical characteristics.

Use in Solar Thermal Collectors

The functional additive package used in FREEZLIGHT® heat transfer fluids is suitable for operation in solar thermal systems.
However, FREEZLIGHT® −20 °C is not recommended for solar collectors because it does not provide a sufficient low-temperature safety margin for equipment and pipelines located outside the building.
Solar collectors are affected by:

• the minimum local temperature;
• prolonged periods of frost;
• strong wind;
• circulation shutdown;
• emergency equipment shutdown;
• possible dilution of the fluid by residual water.

For this reason, we recommend FREEZLIGHT® −32 °C for solar thermal collectors.
Higher pressure in a closed solar thermal circuit raises the boiling temperature of the heat transfer fluid, but it does not prevent thermal ageing during prolonged overheating. The boiling temperature and the permissible continuous operating temperature are different characteristics.
A solar thermal system must have a correctly sized expansion vessel, a functioning safety valve, circulation monitoring, and the overheating and stagnation protection specified by the equipment manufacturer.

Material Compatibility

FREEZLIGHT® −20 °C may be used in systems containing:
• carbon steel;
• stainless steel;
• cast iron;
• copper;
• brass;
• bronze;
• aluminium alloys;
• polypropylene pipes;
• PEX;
• PE-RT;
• multilayer composite pipes.

Final compatibility is determined not only by the pipe material. The boiler design, heat exchanger material, pump seals, gaskets, sealants, expansion vessel diaphragm, and equipment manufacturers’ recommendations must also be considered.
Seals must be suitable for long-term operation with aqueous glycol solutions.

Preparing the System Before Filling

1. Check whether the equipment manufacturer permits the use of propylene glycol heat transfer fluids.
2. Flush rust, sludge, old heat transfer fluid, and other contamination from the system.
3. Remove as much water as possible after flushing or pressure testing.
4. Check the tightness of pipes, threaded joints, valves, pumps, and heat exchangers.
5. Check the condition and capacity of the expansion vessel.
6. Make sure the circulation pump provides the required flow rate.
7. Bleed air successively from all circuits during filling.
8. After the first heating and cooling cycle, recheck the pressure and system tightness.

Aqueous glycol solutions place greater demands on sealing quality than water. Connections that did not leak while operating with water may begin to show slight seepage after the system is filled with heat transfer fluid.

Does the Heat Transfer Fluid Need to Be Diluted

FREEZLIGHT® −20 °C is supplied ready to use. No additional dilution with water is required.
Adding water:

• reduces the propylene glycol concentration;
• raises the crystallization onset temperature;
• reduces the low-temperature safety margin;
• changes the ratio between the base fluid and the additive package.

If water has been added or may remain in the system, the concentration of the heat transfer fluid must be checked after thorough mixing.

Can It Be Mixed with Other Heat Transfer Fluids

We do not recommend mixing FREEZLIGHT® −20 °C with heat transfer fluids of unknown composition.
Different products may contain incompatible corrosion inhibitors, buffering agents, stabilisers, antifoam components, and dyes.
Possible consequences of mixing include:
• cloudiness;
• sediment formation;
• foaming;
• a change in pH;
• reduced corrosion protection;
• blockage of narrow channels;
• shortened service life.
When changing from another product, the system should be drained as completely as possible and flushed.

Important Limitations

The following is not recommended:
• using FREEZLIGHT® −20 °C in outdoor systems without an adequate low-temperature safety margin;
• using it in solar thermal collectors instead of FREEZLIGHT® −32 °C;
• filling external heat pump circuits;
• using it in electrode boilers without the manufacturer’s approval;
• mixing it with heat transfer fluids of unknown composition;
• diluting it with water without subsequently checking the concentration;
• allowing prolonged overheating or local boiling;
• using it in a drinking water circuit;
• filling a contaminated or leaking system.

Operation and Service Life

During operation, monitor:
• system pressure;
• the absence of leaks;
• circulation pump operation;
• the condition of the heat transfer fluid;
• the appearance of sediment;
• changes in colour or odour;
• the amount of water or heat transfer fluid added.
Regular topping up with water indicates a leak. First identify and eliminate the cause, then restore the required heat transfer fluid concentration.
The expected service life of FREEZLIGHT® −20 °C is up to 5 years when the system is correctly prepared and operated.
Overheating, contamination, excessive contact with air, frequent addition of water, and mixing with other products shorten the service life.

Storage and Safety Precautions

Store the heat transfer fluid:
• in a tightly closed container;
• in a covered indoor area;
• protected from direct sunlight;
• away from sources of intense heat;
• separately from food products;
• out of the reach of children and animals.
Propylene glycol heat transfer fluid is less toxic than ethylene glycol formulations, but it is still a technical fluid.
Protective gloves and safety glasses are recommended during handling. Do not allow the product to enter drinking water or food products.
In case of contact with the eyes or skin, rinse the affected area with plenty of water.

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Frequently Asked Questions

What does the −20 °C rating mean?

It is the temperature at the onset of crystallization. With further cooling, the product gradually thickens and circulation may stop.

Is FREEZLIGHT® −20 °C suitable for a private home?

Yes, provided that the entire system is located inside the building, has no outdoor heat exchangers, and does not pass through unheated areas.

Can it be used in underfloor heating?

Yes. After pressure testing the circuits, remove as much water as possible and check the concentration after filling the system.

Does the heat transfer fluid need to be diluted?

No. FREEZLIGHT® −20 °C is supplied ready to use.

Can water be added?

Adding water raises the crystallization onset temperature. After a significant addition of water, check the concentration using a refractometer.

Can FREEZLIGHT® −20 °C be used in solar thermal collectors?

The additive package is suitable for solar thermal systems, but the −20 °C concentration does not provide the recommended safety margin for outdoor collectors and pipelines. We recommend FREEZLIGHT® −32 °C for solar thermal collectors.

When should FREEZLIGHT® −32 °C be selected?

When the system has outdoor sections or rooftop heat exchangers, passes through unheated rooms, or requires a greater low-temperature safety margin.

Can FREEZLIGHT® be mixed with another antifreeze?

It is not recommended. Different additive packages may be incompatible and may impair the properties of the final mixture.

Can automotive antifreeze be used?

It is not recommended. Automotive antifreezes are designed for different materials, temperature conditions, and operating environments.

How long does the heat transfer fluid last?

The expected service life is up to 5 years. Overheating, contamination, leaks, frequent addition of water, and mixing with other products shorten this period.

How to Order FREEZLIGHT® −20 °C

Before ordering, it is advisable to determine:
• the total system volume;
• whether there are outdoor pipelines or heat exchangers;
• the boiler type;
• the minimum temperature of the coldest section;
• the approximate volume of residual water;
• the required package size.
Novohim managers will help determine which heat transfer fluid is suitable for the system design and operating conditions: FREEZLIGHT® −20 °C or FREEZLIGHT® −32 °C.

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