Free tool · HVAC technical
Superheat, subcooling & target superheat calculator
Enter pressures and line temperatures; get superheat, subcooling and a target superheat check.
Superheat
12.0 °F
Suction line temp − suction saturation temp
Subcooling
10.0 °F
Condensing saturation temp − liquid line temp. Compare with the nameplate target (TXV systems).
Target superheat (fixed orifice)
12.0 °F
(3 × wet bulb − 80 − outdoor dry bulb) ÷ 2
Measured is 0.0 °F below target. Within the usual ±5 °F tolerance.
Always follow the manufacturer's charging chart. For blends with glide (e.g. R-454B), use dew point for superheat and bubble point for subcooling.
How it works
Superheat is how far the suction vapor is above its boiling (saturation) temperature; subcooling is how far the liquid is below its condensing temperature. Together they tell you how the system is charged and how it's performing.
Your gauges (or a pressure-temperature chart for the refrigerant) give you the saturation temperatures. This calculator does the subtraction and, for fixed-orifice systems, works out the target superheat from indoor wet bulb and outdoor dry bulb.
The formula
Superheat = suction line temperature − evaporator saturation temperature. Subcooling = condensing saturation temperature − liquid line temperature. Fixed-orifice target superheat = (3 × indoor wet bulb − 80 − outdoor dry bulb) ÷ 2.
Worked example
Example: suction saturation 40 °F and suction line 52 °F gives 12 °F superheat. With 63 °F wet bulb and 85 °F outdoor, the target is (189 − 80 − 85) ÷ 2 = 12 °F, so the charge looks right.
Free download
HVAC Maintenance Checklist (Cooling + Heating)
Printable tune-up checklists for AC, heat pump and furnace visits, with readings to record.
Get it free- Cooling / heat pump tune-up checklist
- Gas furnace tune-up checklist
- Readings log: superheat, subcooling, static pressure, temperature split, amps
- Customer recommendations section
Frequently asked questions
TXV systems hold superheat roughly steady; charge them by subcooling to the manufacturer's target on the nameplate or installation instructions.
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