Calculator
HVAC Superheat & Subcooling Calculator
Read the charge in seconds. Enter your gauge pressures and line temperatures and get actual superheat, actual subcooling, and the verdict — undercharged, overcharged, or correct — against the industry target-superheat chart for fixed-orifice systems or the 8–12 °F subcooling window for TXV and EEV systems. Free, no signup.
Free
Actual superheat
12.2°F
Superheat on target — charge is correct
Correctly charged
Actual superheat
12.2°FSuction line − 44.8°F saturation
Target superheat
11.0°FFrom the indoor wet bulb × outdoor dry bulb chart
Deviation from target
+1.2°FPositive = running hot, typically undercharged or low airflow
Suction saturation (sat.)
44.8°FR-410A at 130 psi
Subcooling (cross-check)
10.1°FTarget 8–12 °F · from the Subcooling tab
Before you charge: verify airflow first
These readings only diagnose the charge once airflow and the refrigerant circuit are known good.
Airflow and a clean circuit come first
Superheat and subcooling only read true on a system with correct airflow and a clean, non-restricted refrigerant circuit. A dirty coil, a collapsed duct, or a restricted metering device will move these numbers exactly like a charge problem.
Never charge by superheat below 5 °F target
When the chart target falls under 5 °F the test is not valid — retest in different conditions or charge by weight. This tool flags it and withholds the verdict when it happens.
Manufacturer charts override these targets
Where the equipment carries its own charging chart, that chart wins. The targets here are the generic industry values and vary a few degrees by OEM.
Target superheat chart (fixed orifice)
Indoor return-air wet bulb across the rows, outdoor condenser-air dry bulb across the columns. A dash means the target is under 5 °F and the test is invalid.
| WB \ DB | 55 | 65 | 75 | 85 | 95 | 105 | 115 | 125 | 128 |
|---|---|---|---|---|---|---|---|---|---|
| 50 | 7.5 | — | — | — | — | — | — | — | — |
| 55 | 15 | 10 | 5 | — | — | — | — | — | — |
| 60 | 22.5 | 17.5 | 12.5 | 7.5 | — | — | — | — | — |
| 65 | 30 | 25 | 20 | 15 | 10 | 5 | — | — | — |
| 70 | 37.5 | 32.5 | 27.5 | 22.5 | 17.5 | 12.5 | 7.5 | — | — |
| 75 | 45 | 40 | 35 | 30 | 25 | 20 | 15 | 10 | 8.5 |
| 76 | 46.5 | 41.5 | 36.5 | 31.5 | 26.5 | 21.5 | 16.5 | 11.5 | 10 |
Values between grid lines are interpolated. TXV and EEV systems are not charged from this chart — use subcooling. Manufacturer charging charts override these values.
R-410A pressure–temperature reference
Near-azeotropic — glide ≈0.2 °F, so one saturation curve is used for both superheat and subcooling.
| Sat. temp | Bubble (liquid) | Dew (vapour) |
|---|---|---|
| 0°F | 48.2 | 48.2 |
| 10°F | 62.3 | 62.3 |
| 20°F | 78.7 | 78.7 |
| 30°F | 97.5 | 97.5 |
| 40°F | 118.9 | 118.9 |
| 50°F | 143.3 | 143.3 |
| 60°F | 170.7 | 170.7 |
| 70°F | 201.5 | 201.5 |
| 80°F | 235.9 | 235.9 |
| 90°F | 274.3 | 274.3 |
| 100°F | 316.9 | 316.9 |
| 110°F | 364.1 | 364.1 |
| 120°F | 416.4 | 416.4 |
| 130°F | 474 | 474 |
| 140°F | 537.6 | 537.6 |
Pressures in psig. Bubble and dew coincide, so one saturation temperature serves both readings.
Industry benchmarks
- Superheat
- Suction line temp − suction sat. temp (dew)
- Subcooling
- Liquid sat. temp (bubble) − liquid line temp
- Fixed orifice / piston
- Charge by target superheat chart
- TXV / EEV
- Charge by subcooling, 8–12 °F
- TXV evaporator superheat
- 8–14 °F (check, not a target)
- Superheat pass band
- ±5 °F of target (Title 24 RA3.2)
- Target superheat floor
- Below 5 °F — do not charge by superheat
What you'll get
Pick superheat or subcooling
Fixed orifice, piston, and cap-tube systems charge by superheat. TXV and EEV systems charge by liquid-line subcooling — the tabs match how the system is actually charged.
Enter your readings
Choose the refrigerant, then add gauge pressure and line temperature. Pressures convert to saturation temperature off the published P-T chart — dew point for superheat, bubble point for subcooling on glide blends like R-454B.
Read the charging verdict
See actual vs. target, the deviation, and whether to add refrigerant, recover, or leave it alone — plus the full target-superheat chart and P-T table for the refrigerant you selected.
How it works
- 1
Pick superheat or subcooling
Fixed orifice, piston, and cap-tube systems charge by superheat. TXV and EEV systems charge by liquid-line subcooling — the tabs match how the system is actually charged.
- 2
Enter your readings
Choose the refrigerant, then add gauge pressure and line temperature. Pressures convert to saturation temperature off the published P-T chart — dew point for superheat, bubble point for subcooling on glide blends like R-454B.
- 3
Read the charging verdict
See actual vs. target, the deviation, and whether to add refrigerant, recover, or leave it alone — plus the full target-superheat chart and P-T table for the refrigerant you selected.
How superheat and subcooling tell you the refrigerant charge
Superheat is how far the suction vapour has risen above its saturation temperature: suction line temperature minus the saturation temperature at the measured suction pressure. Subcooling is the mirror image on the high side: the saturation temperature at the liquid-line pressure minus the actual liquid line temperature. Between them they tell you whether the evaporator is being fed enough refrigerant and whether liquid is stacking up in the condenser — which is why every charging procedure in the trade comes back to these two numbers.
Which one sets the charge depends on the metering device. A fixed orifice, piston, or capillary tube has no way to control superheat, so superheat moves with load and the charge is set against a target read from the indoor return-air wet bulb and the outdoor dry bulb. A TXV or EEV holds superheat itself, so superheat tells you nothing about charge on those systems — the charge is set by liquid-line subcooling, typically 8–12 °F. Both methods assume correct airflow and a clean, unrestricted system, and both are overridden by the manufacturer’s own charging chart when one is on the unit.
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View statesSuperheat & Subcooling Calculator FAQs
How do you calculate superheat and subcooling?
Superheat = suction line temperature − the saturation temperature at the measured suction pressure. Subcooling = the saturation temperature at the liquid-line pressure − the liquid line temperature. Both saturation temperatures come off the refrigerant’s pressure-temperature chart. On a glide blend such as R-454B, superheat uses the dew point and subcooling uses the bubble point.
What is a good superheat and subcooling reading?
On a fixed-orifice system, actual superheat should land within about ±5 °F of the chart target for your indoor wet bulb and outdoor dry bulb — many techs charge to ±3 °F. On a TXV or EEV system, liquid-line subcooling should be 8–12 °F, with evaporator superheat typically 8–14 °F as a performance check rather than a charging target.
Do you charge a TXV system by superheat or subcooling?
By subcooling. A thermostatic or electronic expansion valve modulates to hold superheat, so superheat stays roughly constant whether the system is undercharged or overcharged. Liquid-line subcooling, typically 8–12 °F, is what actually moves with charge on a TXV or EEV system.
Is this superheat and subcooling calculator free?
Yes. Every tool on CloseCrew is free for HVAC contractors — no account required.
