Target Superheat Calculator
For piston and cap-tube systems. Enter indoor wet bulb and outdoor dry bulb to get the target superheat.
How it works
Target superheat = ((3 × indoor wet bulb) − 80 − outdoor dry bulb) ÷ 2
This is the formula behind the superheat charging charts that ship with fixed-orifice equipment. The charts cover indoor wet bulb from about 50 to 76 °F and outdoor dry bulb from about 55 to 115 °F. When the target comes out below 5 °F, the chart leaves that box blank: don't charge by superheat, weigh in the charge instead.
Getting good readings
- Indoor wet bulb: measure return air at the evaporator, not at a grille across the house.
- Outdoor dry bulb: measure air entering the condenser coil, in the shade.
- Check airflow first. Low airflow pushes superheat down and makes an undercharge look correct.
- Do not use this target on TXV or EEV systems; charge those by subcooling with the superheat & subcooling calculator.
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Results are estimates for field reference. Always confirm against the equipment manufacturer's charging chart, installation instructions and local code. Found a problem with this tool? Tell us.