Calculate HVAC refrigerant superheat from suction-line and saturation temperatures, or solve for the required line or saturation temperature, in °F or °C.

Use the saturation temperature that matches suction pressure and refrigerant on a P-T chart or gauge.

Superheat Formula

The following example problem outlines the steps and information needed to calculate the superheat.

SH = T₍suction) - Tₛₐₜ

Variables:

  • SH is the superheat (a temperature difference, in °F or °C)
  • Tsuction is the measured refrigerant vapor temperature at the evaporator outlet / suction line (often measured near the compressor inlet), in °F or °C
  • Tsat is the saturation temperature that corresponds to the measured suction pressure for the same refrigerant, in °F or °C

To calculate the superheat, subtract the saturation temperature (from pressure) from the measured suction line (vapor) temperature.

How to Calculate Superheat?

The following steps outline how to calculate the superheat.

  1. First, measure the suction line (vapor) temperature at the evaporator outlet / compressor inlet (°F or °C).
  2. Next, measure the suction pressure and use the correct refrigerant P-T chart (or gauge scale) to determine the corresponding saturation temperature (°F or °C).
  3. Next, gather the formula from above: SH = Tsuction – Tsat.
  4. Finally, calculate the superheat.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

suction line temperature (°F) = 51

saturation temperature (°F) = 24

SH = Tsuction – Tsat = 51 – 24 = 27 °F