ProTherm™ HT-21 Mineral Oil Type


ProTherm HT-21 is specially formulated heat transfer oil for heavy duty industrial heating systems. Extremely pure API Group II or Group II+ base stocks are carefully selected and additized with a powerful high temperature anti-oxidant blend. This produces a finished product which is highly resistant to the thermal oxidation process and its effects on the fluid, such as viscosity increase, chemical breakdown, and sludge or varnish formation. ProTherm HT-21 is a tough industrial fluid which will not foul heat transfer surfaces if used within normal operating and maintenance procedures.

ProTherm HT-21 is recommended for applications requiring up to 400 degrees F in open systems, and 600 F in closed systems.


Viscosity 43 cSt 40C

Flash Point, COC, F 420F

Pour Point, F 0

at 500F:

Thermal Conductivity 0.067 BTU/Hr/Ft2/ oF /Ft.

Heat Capacity 0.656 BTU/lb/oF

Specific Gravity 0.72

Vapor Pressure 25 mm Hg