How to avoid thermal oil freezing

It’s a common misconception that the Inuit language contains hundreds of words for snow and ice. In reality, they have about the same amount of root words that mean frozen water as the English Language

Inuits may not have more words for cold conditions, but they do have a deep understanding of the impact of frozen weather — which cannot always be said for UK manufacturers using thermal oil.

Here Clive Jones, Managing Director of thermal fluid supplier Global Heat Transfer explains how thermal oil freezing occurs and offers his tips for preventing frozen fluid.

The consequences of a thermal oil freezing can be both damaging and costly in any application. Frozen thermal oils mean that heat can’t be brought to temperature at the appropriate point in the application, resulting in downtime, lost production and, potentially, lost customers.

Understanding freezing points

To avoid the problems associated with freezing oil, it’s critical to first understand thermal fluid qualities as well as the needs of your application.

Most heat transfer fluids are designed to operate at extremely high temperatures, of between 340 and 400 °C for instance. These high temperature fluids will freeze at 0 °C or higher, some as high as 15 °C.

Just as certain fluids are intended to be used at ultra-high operating temperatures others as specifically for use in low temperatures.

A typical low temperature fluid might be operable between -50 and +120–220 °C, with an extremely versatile fluid functioning between temperatures as extreme as -90 and +300 °C.

The easiest way get the right heat transfer fluid for your application is to consult a specialist who can clearly explain the temperature extremes at which each fluid can operate.

Most responsible providers will also offer charts that clearly delineate the extremes that their own oils can withstand, either on their websites or on request.

Returning to production

If thermal oil does solidify, you have to rely on ambient temperature to restore it to its former viscosity, as the application of focused heat isn’t an appropriate way of melting the fluid.

The worst thing you can do is to attempt to use a system when the oil is already frozen. This could cause serious damage to the pump and associated peripherals such as the motor and potentially any control equipment.

The best way to avoid downtime caused by frozen fluid is to take steps to prevent freezing.


Optimal system and storage design and location can prevent these issues from occurring. There may well be other factors that have greater sway over the system design and location of each point in the process and even over the design of the pipework.

However, under normal circumstances it should be possible to choose storage locations that allow oil to be kept at a reasonable ambient temperature at all times.

Avoiding oil freezing

There are a number of issues to address to help avoid the problems caused by freezing oil. First, when maintaining thermal oil that is currently in use, leave the circulation pump running when the boiler is not on.

The friction and heat from the pump will keep the oil at a sufficiently high temperature to ensure it doesn’t freeze.

There are also measures that can be taken to protect stock oil that isn’t already in use in your system. Make sure that this oil, especially ‘top oil’ that might need to be called into use quickly, is stored inside.

If this is impossible, or in cases where oil is stored in an unheated building such as a shed or warehouse, purpose designed barrel warmers can be provided by your thermal oil supplier.

Temperature drops

Frozen heat transfer oil commonly occurs as a result of winter shutdowns or periods of low production output, when ambient temperatures in the plant and storage areas are often allowed to drop.

Heating up the system very slowly after the shutdown is important just in case there is condensation in the system and the fluid.

The next step, if the temperature has been extremely low, is to heat up the ring main first and then introduce the heat exchangers one at a time.

Both of these steps will help to minimise the impact on the system itself and reduce any potential damage.

We might not need to develop hundreds of terms for snow and ice — but manufacturers should understand how to prevent the negative effects of these weather conditions.

By taking steps to select the right fluid for the application, introduce measures to protect the systems during winter shutdowns and protecting stock fluid, manufacturers can maintain production whatever the weather.