Selection and comparison of thermic fluids in a fired heater Selection and comparison of thermic fluids in a fired heater Hot oil, also called thermic fluid, is a heat transfer fluid (HTF) used in oil refineries and chemical plants. Hot oil, also called thermic fluid, is a heat transfer fluid (HTF) used in oil refineries and chemical plants. HTF transfers heat to the process fluid using sensible heat. Many limitations exist to using steam as a heat source. The steam pressure must be high enough to get the high temperatures required for the process; a steam system also requires water treatment and condensate collection systems; and steam systems are also a common leak point within plants. Conversely, steam is non-toxic and non-flammable, so there is zero negative impact to the environment.