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

Use line and saturation temperatures from the same measurement point; for blends, use the dew-point saturation temperature.

Read from your refrigerant’s P–T chart at the measured suction pressure.

Optional settings

Superheat Formula

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

SH = Tsuction - Tₛₐₜ

Variables:

  • SH is the superheat (a temperature difference, in °F or °C)
  • Tsuction is the measured line temperature at the chosen location, in °F or °C. Evaporator-outlet superheat and compressor-inlet/total superheat use different measurement locations.
  • Tsat is the vapor/dew-point saturation temperature for the same refrigerant at the pressure corresponding to that location, in °F or °C. For refrigerant blends, use vapor/dew point rather than liquid/bubble point.

Subtract the corresponding vapor/dew-point saturation temperature from the measured line temperature. Match pressure and temperature to the chosen location, accounting for suction-line pressure loss when needed. Reverse solves use line temperature = saturation temperature + desired superheat, or saturation temperature = line temperature − desired superheat. A negative measured difference is retained for review: verify refrigerant, pressure, probe location, readings and operating conditions; it does not diagnose a particular fault. See Parker/Sporlan’s measurement guidance, Danfoss’s dew-point explanation, and the Fieldpiece SM380V manual.

How to Calculate Superheat?

The following steps outline how to calculate the superheat.

  1. First, choose the measurement location and measure the line temperature there (°F or °C). Keep evaporator-outlet and compressor-inlet/total superheat measurements distinct.
  2. Next, obtain the pressure corresponding to that location and use the correct refrigerant P-T chart or gauge scale to determine vapor/dew-point saturation temperature (°F or °C). Account for pressure loss if the pressure is measured elsewhere.
  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 Δ°F = 15 Δ°C. Superheat is a temperature difference: Δ°C = Δ°F × 5/9, without a 32-degree offset. Absolute temperatures instead use °C = (°F − 32) × 5/9. Desired superheat is a user-specified nonnegative difference; follow the equipment’s procedure rather than assuming a universal target.