Free Calculator
Superheat Calculator
Enter suction pressure and line temperature for R-410A, R-22, or R-134a to get actual superheat, target superheat, and a quick refrigerant-charge diagnosis in the field.
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Check Superheat and Refrigerant Charge
Pick your refrigerant and metering device, enter your gauge and line-temperature readings, and see how your actual superheat compares to target.
Used for the pressure-to-saturation-temperature lookup.
Read from the low-side manifold gauge.
Measured with a clamp thermometer on the suction line.
📋 Important: All calculator results are ballpark estimates
The figures shown are approximate estimates based on interpolated pressure-temperature data and should be used as a field reference only. They are not a substitute for the equipment manufacturer's charging specifications, calibrated instruments, or verified airflow. Actual superheat and the correct charge will vary based on your gauges, thermometers, system condition, and operating conditions. Always confirm against manufacturer data and a stabilized system before adding or recovering refrigerant.
How to Read and Use Superheat
What superheat actually measures
Superheat is the number of degrees the refrigerant vapor sits above its saturation (boiling) temperature at the measured low-side pressure. You find it by converting suction pressure to a saturation temperature with a pressure-temperature relationship, then subtracting that from the actual suction line temperature:
| Reading | What it usually means |
|---|---|
| Superheat well below target | Overcharge, or liquid flooding back to the compressor |
| Superheat near target | Charge and evaporator load are in a healthy range |
| Superheat well above target | Undercharge, restriction, or low indoor airflow |
| Zero / near-zero superheat | Liquid refrigerant reaching the compressor — stop and diagnose |
Superheat is one data point. Pair it with subcooling, delta-T, and airflow before concluding anything about the charge.
Why TXV and fixed-orifice targets differ
A thermostatic or electronic expansion valve (TXV/EEV) actively modulates refrigerant flow to hold a nearly constant superheat across a wide range of loads — so its target is a fixed value near 10°F (roughly an 8–12°F window), and you charge these systems to subcooling with superheat as a cross-check. A fixed-orifice or piston metering device can't adjust flow, so its superheat drifts with indoor and outdoor conditions. That's why fixed-orifice systems are charged to a target superheat that changes with the weather, read from a charging chart or calculated from indoor wet-bulb and outdoor dry-bulb temperatures.
The fixed-orifice target formula
The common field approximation for fixed-orifice target superheat is ((3 × indoor wet-bulb) − 80 − outdoor dry-bulb) ÷ 2. As indoor humidity/load rises, target superheat climbs; as outdoor temperature rises, it falls. This calculator applies that formula and clamps the result to a sensible 5–35°F range. It's a starting point — the equipment manufacturer's charging chart always takes precedence when one is available.
Accurate readings depend on your instruments and airflow
A superheat number is only as good as the inputs behind it. Use calibrated gauges and a good clamp thermometer clamped tight to a clean section of suction line near the service valve, let the system run and stabilize for 10–15 minutes, and confirm airflow is in range (typically about 400 CFM per ton) before trusting the diagnosis. Low indoor airflow — a dirty filter, collapsed duct, or slipping blower — can mimic an undercharge by driving superheat high. This tool is a field aid, not a replacement for proper procedure. If you manage a team of techs, standardized job workflows in HVAC Contractor Software help make sure every diagnosis and charge is documented the same way.
Before you add or recover refrigerant
- Confirm the correct refrigerant for the system and use the matching pressure-temperature data
- Verify airflow is in range before blaming the charge
- Let the system stabilize before taking readings
- Cross-check superheat with subcooling (especially on TXV/EEV systems)
- Always follow the manufacturer's charging chart and EPA refrigerant-handling requirements
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Book a Free DemoFrequently Asked Questions
What is superheat and why does it matter?
Superheat is the number of degrees a refrigerant vapor has been heated above its saturation (boiling) temperature at a given pressure. It's measured at the suction line by subtracting the saturation temperature from the actual suction line temperature. Superheat tells a technician whether the evaporator is fully using the refrigerant charge — too little superheat suggests an overcharge or liquid flooding back to the compressor, while too much suggests an undercharge or a starved evaporator.
How do I calculate superheat?
Measure the low-side (suction) pressure with a manifold gauge and convert it to a saturation temperature using a pressure-temperature chart for your refrigerant. Then measure the actual suction line temperature at the service valve with a clamp thermometer. Subtract the saturation temperature from the measured line temperature. The difference is your actual superheat in degrees Fahrenheit. This calculator does the pressure-to-temperature lookup for R-410A, R-22, and R-134a automatically.
What is a good superheat reading?
For a system with a TXV or EEV, target superheat is typically a fixed value around 10°F, with an acceptable range of roughly 8–12°F. For a fixed-orifice or piston system there is no single number — the correct target depends on indoor wet-bulb and outdoor dry-bulb temperature and is read from a charging chart. This tool applies the standard charging-chart formula for fixed-orifice systems so you can compare your actual reading to the right target for the current conditions.
Why is target superheat different for TXV versus fixed-orifice systems?
A TXV (or EEV) actively modulates refrigerant flow to hold a nearly constant superheat regardless of load, so the target is a fixed number near 10°F and you charge to subcooling instead. A fixed-orifice or piston metering device cannot adjust flow, so its superheat drifts with indoor and outdoor conditions. That's why fixed-orifice systems are charged to a target superheat that changes with the weather, read from a manufacturer charging chart or calculated from wet-bulb and dry-bulb temperatures.
Can I rely on this superheat calculator to charge a system?
No — treat it as a field aid, not a substitute for proper procedure. The pressure-to-temperature values here are interpolated from a small anchor table and are approximate. Real charging depends on accurate, calibrated gauges and thermometers, correct airflow (typically 400 CFM per ton), a stabilized system, and the equipment manufacturer's specifications. Always verify against manufacturer charging data and confirm airflow before adding or removing refrigerant.
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Get a Free DemoAll results are approximate field-reference figures based on interpolated pressure-temperature data and should be verified against the equipment manufacturer's charging specifications and calibrated instruments before adding or recovering refrigerant.