Heat Transfer Fluids

For non-pressurized closed-loop thermal systems

HR Synthetic-Aromatic HTF

HR Synthetic-aromatic Thermal Fluid


HR synthetic-aromatic heat transfer fluid is an alkylated-aromatic based heat transfer fluid formulated for closed-loop liquid phase heating to 650°F in fired heaters and 675°F in waste heat recovery and full convection heaters. HR synthetic-aromatic thermal fluid offers greater thermal stability than competitive aromatic based fluids that cover similar temperature ranges. Testing (ASTM D6743) shows that, compared to its closest competitor, HR synthetic-aromatic heat transfer fluid experiences 1/2 the amount of fluid degradation when maintained at 700°F for 500 hours. Less degradation means less maintenance and a longer fluid life. Centrifugal pumps are generally specified around the fluid viscosity at the desired operating temperature (usually less than 2 cps). Capacity falls off significantly above 300 cps. So the actual minimum start-up temperature of a fluid is where the viscosity curve crosses the 300 cps line. HR Synthetic-Aromatic Heat Transfer Fluid’s lower cold start-up temperature of 13°F (-11°C) offers a significant advantage over other high-temperature fluids.


Minimum Startup Temp (300cSt)Maximum Operating Temp
11°F / -12°C675°F / 357°C


  • Best in class thermal stability and heat transfer efficiency
  • Widest operating range
  • Unique formulation resists thermal decomposition at high temps


Note: If you are experiencing short supply, or long lead times for your currently specified synthetic/aromatic 650°F (terphenyl or alkylated aromatic) heat transfer fluid, call Paratherm for a point-by-point comparison of physical properties. We have product available, and may have just the fluid for your application. +1 (610) 860-6323. Or, use the links on the left side of this page to compare properties with Therminol 66.


PropertyParatherm HRTherminol 66
Chemical CompositionAlkylated AromaticModified Terphenyl
Maximum Operating Temperature650°F (343ºC)650°F (343°C)
Maximum Film Temperature700°F (371 C)705°F (374°C)
Minimum Start-up Temp (300 cSt)11.0°F (-12°C)52.0°F (11°C)
Kinematic Viscosity @ 40 C11.0 cSt29.6 cSt
Kinematic Viscosity @ 100 C2.4 cSt3.8 cSt
Density @ 25 C7.98 lb/gal (956 kg/m3)8.39 lb/gal (1005 kg/m3)
**Degree of Decomposition (ASTM D6743)0.150.56

*Therminol 66 is a trademark of Solutia Inc.

**The Degree of Decomposition, measured through ASTM D6743, reflects the overall thermal degradation of a thermally stressed fluid at a specific test temperature. It is determined by adding the total mass percentage of all decomposed products found in a thermally stressed sample. These values were found after both fluids were tested side-by-side at 370ºC (698ºF) for 500 continuous hours. A lower Degree of Decomposition reflects superior relative Thermal Stability of a fluid.

Mobile users view full PDF here: 2022-HR-ID.pdf

Mobile users view full PDF here: PARATHERM-HR-SDS.pdf

Paratherm™ HR Synthetic-Aromatic HTF


Chemical NameAlkylated Aromatic
OdorSlight Odor
Maximum Recommended FilmTemperature700°F / 371°C
Maximum Recommended Oper. Temperature-Fired Heaters650°F / 343°C
Maximum Recommended Oper. Temperature-All Others675°F / 357°C
Minimum OperatingTemperature 20cPs (20 mPa-s)78°F / 26°C
Minimum Start-upTemperature 300cPs (300 mPa-s)11°F / -12°C
Viscosity @ 60°F / 15.5°C cSt (mm2//sec)36
Density @ 60°F / 15.5°Clb/gal (kg/m3)8 (964)
Flash Point Pensky-Martens Closed Cup (D-93)>300°F (149°C)
Autoignition Temperature (Maximum 10 second ignition delay)>780°F/416°C)
Boiling Point (14.7 psia/101 kPa)638°F/337°C
Vapor Pressure @ Maximum operating temp psia (kPa)28.8/195
% Volume expansion over recommended operating temperature per 100°F (°C)5.5 (9.9)
Average Molecular Weight240

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