Superheat Calculator
Free superheat calculator for HVAC techs. Enter the suction line temperature and the saturation temperature to get measured superheat in °F, with target ranges for TXV and fixed-orifice systems.
How the superheat calculation works
Superheat is the number of degrees the refrigerant vapor has risen above its saturation (boiling) temperature at the suction pressure. It tells you how much of the evaporator is being used to boil liquid into vapor versus how much is just heating already-boiled vapor.
The formula is simple:
Superheat (°F) = Suction Line Temperature − Saturation Temperature
The saturation temperature is not measured directly — you read the low-side (suction) pressure on your gauges and convert it to a saturation temperature using the pressure–temperature (P/T) chart for the specific refrigerant in the system. Most digital manifolds do this conversion automatically once you select the refrigerant.
Worked example
A R-410A system reads a suction line temperature of 52°F and the gauges show a suction saturation temperature of 40°F:
52 − 40 = 12°F of superheat
On a TXV system, 12°F sits right at the top of the normal 8–12°F band — a healthy reading.
What your superheat reading is telling you
- TXV / EEV systems hold superheat fairly constant (typically 8–12°F) across a range of conditions, because the valve modulates to maintain it. If a TXV system is far outside that band, suspect the charge, airflow, or the valve itself.
- Fixed-orifice (piston) systems do not control superheat — it floats with indoor and outdoor conditions. There is no single “correct” number. You compare the measured superheat to a target superheat calculated from the indoor wet-bulb and outdoor dry-bulb temperatures.
| Reading | Likely meaning |
|---|---|
| Low superheat (under ~5°F) | Overcharge, TXV overfeeding, or low evaporator airflow — risk of liquid floodback |
| Normal (8–12°F on a TXV) | System is charged and metering correctly |
| High superheat (over ~14°F) | Undercharge, restriction, or a starving metering device |
Superheat and subcooling are read together. On a TXV system you charge to subcooling and use superheat as a check; on a fixed-orifice system you charge to superheat.
How FieldPad helps in the field
This calculator gives you the number on the spot. FieldPad keeps it with the work: log the reading against the equipment profile and the client, attach it to the service job, and turn the diagnosis into a signed estimate or invoice without re-keying anything. Your charging history lives on the same equipment record as the invoices, so the next visit starts where this one left off.
Stop Re-Running These Numbers by Hand
FieldPad is the all-in-one iPhone CRM for solo HVAC techs — clients, scheduling, estimates, invoices with signatures, inventory, and equipment history. Keep your readings on the job, the client, and the equipment, all in one offline-ready app. EPA Section 608 and Subpart C compliance included.
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