Does the term Thermal Fluid refer to a special fluid?

The term Thermal Fluid does not refer to a specific fluid, there are many. There are also many companies that produce a variety of Thermal Fluids.

The most common Thermal Fluids are either Mineral Oil based or Synthetic Oils. The various manufacturers typically produce a series of fluids that each has a recommended operating temperature range. Close consideration should be given to this operating range in selecting a fluid.

There are other considerations as well, consult with fluid manufacturers to get their fluid recommendation for your application.

An improperly selected fluid could have an extremely short life and could have detrimental effects on the heater.