Superheat and Subcooling Calculator
Enter the pressures from your gauges and the line temperatures from your clamps. The calculator converts pressure to saturation temperature for your refrigerant and returns superheat (suction line temperature minus evaporator saturation) and subcooling (condenser saturation minus liquid line temperature). For zeotropic blends such as R-454B and R-407C it uses the dew point for superheat and the bubble point for subcooling, as the manufacturers specify.
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Read the how-to guide
The method
- Superheat = suction line temperature − saturation temperature at the suction pressure (dew point for blends).
- Subcooling = saturation temperature at the liquid pressure (bubble point for blends) − liquid line temperature.
- Target superheat for fixed orifice systems uses the common field formula (3 × indoor wet-bulb − 80 − outdoor dry-bulb) ÷ 2. Always prefer the charging chart on the unit or the manufacturer's data.
- Typical targets: TXV systems usually run 8 to 12°F of subcooling (check the nameplate), and superheat 8 to 14°F at the evaporator.
Pressure-temperature data comes from the NIST REFPROP-class equations of state (CoolProp). R-454B is not in CoolProp, so it is modeled as a 68.9/31.1 weight-percent R-32/R-1234yf blend and checked against the published Opteon XL41 pressure-temperature table. Use the manufacturer table for warranty work.
Worked example
R-410A with 118 psig suction (saturation 39.8°F) and a 55°F suction line gives 15.2°F superheat. A 340 psig liquid line (saturation 104.6°F) at 95°F gives 9.6°F subcooling, right in the usual 8 to 12°F range for a TXV system.
Frequently asked questions
Why dew point for superheat and bubble point for subcooling?
Zeotropic refrigerants boil over a range of temperatures (glide). Vapor is fully saturated at the dew point, and liquid at the bubble point, so those are the reference points for superheat and subcooling.
Where do I clamp the thermometers?
Suction line temperature goes about 6 inches from the compressor (or 6 in. from the service valve on the outdoor unit). Liquid line temperature goes at the condenser outlet or the liquid service valve, insulated from ambient.
What is a normal superheat?
It depends on the metering device and conditions. TXV systems are commonly 8 to 14°F; fixed-orifice systems vary with load and should be charged to the manufacturer's superheat chart.
Is this accurate for R-454B?
It is calibrated to published Opteon XL41 values to within about 1°F over the usual range. If your work requires exact values, use the table printed by the manufacturer.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.