Superheat Calculator
Enter your suction-line pressure and temperature for any refrigerant; get superheat plus diagnostic context. Correct dew-curve math for zeotropic blends so high-glide refrigerants (R-407C, R-454C, R-455A) don't read 11–22°F high at a 40°F dew point.
Updated October 26, 2026
Target superheat reference
Target superheat depends on the metering device. These ranges are general guidance; always defer to the equipment manufacturer's charging procedure[2].
| System type | Target superheat | Reference |
|---|---|---|
| Fixed orifice (residential AC) | 5–45°F, read from a chart of indoor wet-bulb and outdoor dry-bulb | California Title 24, Table RA3.2-2[1] |
| TXV (AC and heat pump) | 8–12°F typical; up to 15°F on high-TD coils | Sporlan Bulletins 10-9 and 10-11[2][3] |
| EXV | set by the equipment's controls | the manufacturer's figure |
| Refrigeration, medium temperature (40 to 0°F evaporator) | 6–8°F (Sporlan); 6–10°F at a 10°F design TD (Heatcraft) | [2][4] |
| Refrigeration, low temperature (0 to −40°F evaporator) | 4–6°F | [2] |
For fixed-orifice systems use the manufacturer's charging chart with outdoor dry-bulb and indoor wet-bulb temperatures rather than a single setpoint[1]. See Carrier R-410A charging chart for an example.
Chart range for R-410A: −40°F to 150°F.
What superheat is and why we measure it
Superheat is the temperature of refrigerant vapor above its saturation temperature at the same pressure. At any pressure, the saturation temperature is the boundary where liquid and vapor coexist; once the refrigerant has fully boiled, every degree above that saturation reading is one degree of superheat.
On a working HVAC system, suction-line superheat serves two simultaneous purposes. First, it protects the compressor: positive superheat means no liquid is reaching the suction (liquid in the cylinder is essentially incompressible). Copeland lists valve-plate, piston and connecting-rod damage from low superheat[8], and bearing wear from oil diluted by liquid floodback[9]. Second, it tells you whether the evaporator is being fed correctly: too little superheat means liquid is leaving the evaporator unboiled (wasted capacity); too much means the evaporator is starved.
Schematic of a residential split-system suction line, showing the temperature sensor clamped to the suction line near the outdoor unit's suction service valve and insulated from the air[1], and where the suction pressure is read. Source: California Title 24 Reference Appendix RA3.2[1].
Two metering devices, two different questions
What you do with a superheat reading depends entirely on whether the system uses a fixed-orifice metering device (piston, capillary tube, accurator) or a thermostatic expansion valve (TXV / EEV).
| Metering device | Charge by | Verify by | Typical SH |
|---|---|---|---|
| Fixed orifice (piston, captube) | Superheat (target from chart) | Match fixed-orifice chart target | 5–45°F (from the chart)[1] |
| TXV (thermostatic expansion valve) | Subcooling (charge to SC target) | Steady SH at TXV setpoint | 8–12°F typical, up to 15°F[2][3] |
| EEV (electronic expansion valve) | Subcooling | EEV control board diagnostic | set by its controls |
Fixed-orifice devices have no feedback control, so superheat varies with charge, ambient, and indoor load. Charging a fixed-orifice system means adjusting refrigerant mass until superheat lands on the fixed-orifice charging-chart target value for the current indoor wet bulb / outdoor dry bulb conditions. A TXV modulates flow to hold a nearly constant superheat at the evaporator outlet[2].
On TXV / EEV systems, charge is set by subcooling instead[1]. Superheat on these systems shows whether the valve is working: Title 24 sets the charge by subcooling and uses superheat to check the metering device[1]. On a TXV system, confirm the charge by subcooling first; superheat outside the manufacturer's figure after that (Title 24's default window is 4–25°F) points to the metering device[1]. Sporlan's causes of high superheat on a TXV also include a refrigerant shortage, moisture and dirt[3].
Target superheat reference — fixed-orifice charging charts and OEM service literature
The fixed-orifice charging chart targets superheat based on the indoor wet-bulb temperature entering the evaporator coil and the outdoor dry-bulb temperature at the condenser[1]. Higher indoor WB and lower outdoor DB both raise the target[1]. The interactive matrix below computes the target with the field formula round((3 × WB − 80 − DB) / 2); Title 24 Table RA3.2-2 governs where they differ, and the chart or label on the specific unit always takes precedence.
Measured in the return plenum with a wet-bulb sensor[1]. Title 24's table covers 50–76°F return-air wet-bulb[1].
Shaded thermometer near the condenser. Design condition: 95°F, the outdoor temperature of the AHRI 210/240 full-load "A" rating test[6].
| WB \ DB | 55°F | 60°F | 65°F | 70°F | 75°F | 80°F | 85°F | 90°F | 95°F | 100°F | 105°F | 110°F | 115°F |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 50°F | 8 | 5 | — | — | — | — | — | — | — | — | — | — | — |
| 52°F | 11 | 8 | 6 | — | — | — | — | — | — | — | — | — | — |
| 54°F | 14 | 11 | 9 | 6 | — | — | — | — | — | — | — | — | — |
| 56°F | 17 | 14 | 12 | 9 | 7 | — | — | — | — | — | — | — | — |
| 58°F | 20 | 17 | 15 | 12 | 10 | 7 | — | — | — | — | — | — | — |
| 60°F | 23 | 20 | 18 | 15 | 13 | 10 | 8 | 5 | — | — | — | — | — |
| 62°F | 26 | 23 | 21 | 18 | 16 | 13 | 11 | 8 | 6 | — | — | — | — |
| 64°F | 29 | 26 | 24 | 21 | 19 | 16 | 14 | 11 | 9 | 6 | — | — | — |
| 66°F | 32 | 29 | 27 | 24 | 22 | 19 | 17 | 14 | 12 | 9 | 7 | — | — |
| 68°F | 35 | 32 | 30 | 27 | 25 | 22 | 20 | 17 | 15 | 12 | 10 | 7 | — |
| 70°F | 38 | 35 | 33 | 30 | 28 | 25 | 23 | 20 | 18 | 15 | 13 | 10 | 8 |
| 72°F | 41 | 38 | 36 | 33 | 31 | 28 | 26 | 23 | 21 | 18 | 16 | 13 | 11 |
| 74°F | 44 | 41 | 39 | 36 | 34 | 31 | 29 | 26 | 24 | 21 | 19 | 16 | 14 |
| 76°F | 47 | 44 | 42 | 39 | 37 | 34 | 32 | 29 | 27 | 24 | 22 | 19 | 17 |
— = target below 5°F: Title 24 says a valid charge test can't be performed at these conditions[1].
Field formula, not the Title 24 table; Table RA3.2-2 governs where they differ.[1]
Heat pumps: American Standard's installation instructions approve checking the charge only in cooling mode[5].
Target superheat ranges across HVAC applications. Title 24's targets are read on the suction line near the outdoor unit's service valve[1].
Real service problems solved with the superheat measurement
8 field scenarios spanning residential AC charging (fixed-orifice and TXV), walk-in commercial refrigeration with wide-glide zeotropic blends, and slugging-risk pattern recognition. Each shows what gets measured, the PT chart lookup that converts suction pressure to saturation temperature, the superheat derivation, and a verdict on what to do.
Charging a new R-410A residential AC by superheat target
Scenario · Brand-new R-410A residential AC, piston metering device, 95°F outdoor dry bulb, 63°F indoor wet bulb (75°F return air, 50% RH). You need to set the charge by superheat per the manufacturer's charging instructions, cross-checked against the fixed-orifice charging chart.
Verifying TXV operation on a commissioned R-410A system
Scenario · R-410A TXV-equipped residential AC, just commissioned. Charge was set by subcooling (10°F target). You want to verify the TXV is regulating superheat correctly before signing off.
High superheat — diagnosing undercharge vs restriction
Scenario · Same R-410A TXV system, two months later. Customer reports poor cooling on a 95°F day. Suction pressure looks low and the suction line feels warmer than expected.
Low superheat — overcharge or TXV flooding the evaporator
Scenario · R-410A TXV system after a service add by a previous tech. The compressor is running noticeably louder than normal and you suspect liquid floodback.
Zero superheat — emergency slugging shutdown
Scenario · Legacy R-22 split system reported as 'making knocking noise'. You arrive on-site, hook up gauges, and find concerning numbers. The compressor sound is consistent with hydraulic events.
R-407C medium-temp commercial — why curve selection matters
Scenario · R-407C retrofit on a medium-temp commercial unit (reach-in deli case), 25°F evaporator target. R-407C is zeotropic with ~11°F glide, so the bubble vs dew distinction is significant for superheat calculation.
R-454C low-temp walk-in freezer superheat charging
Scenario · R-454C walk-in freezer (low-temp commercial), −20°F target evaporator temperature, 95°F ambient. R-454C is a wide-glide zeotropic blend used as a low-GWP replacement for R-404A in commercial refrigeration.
R-32 vs R-454B superheat targets — same as R-410A?
Scenario · New installation choosing between R-32 (pure) and R-454B (zeotropic ~2°F glide) for residential AC. Field tech asks: do these A2L refrigerants need different superheat targets than R-410A?
Glide-aware curve selection — why dew is the right curve for superheat
Zeotropic blends boil across a temperature range at constant pressure. As liquid refrigerant enters the evaporator (bubble point) and progresses to fully vaporized (dew point), the saturation temperature rises by the glide value, even though the pressure is unchanged.
Suction-line superheat is measured downstream of the evaporator, where refrigerant is fully vaporized. The relevant saturation reference is the dew point: the temperature at which the last drop of liquid disappeared. Using the bubble point would treat the entry-side saturation as if it were the exit-side reference, overstating superheat by the glide value (bubble sits below dew, so subtracting it inflates the result).
R-407C bubble and dew saturation curves over the service range, showing the consistent 11°F glide between the two. Use the dew curve at suction pressure for superheat (suction line); use the bubble curve at discharge pressure for subcooling (liquid line). Source: CoolProp 7.2.0 saturation data for R-407C.
Glide values across common HVAC blends: R-454B ≈ 2°F, R-448A ≈ 10°F, R-449A ≈ 10°F, R-407C ≈ 11°F, R-454C ≈ 14°F, R-455A ≈ 22°F. Wrong-curve selection on R-455A would shift superheat by 22°F, easily enough to invalidate a charging decision or trigger an unnecessary compressor protection shutdown.
Six common superheat measurement mistakes
- Wrong curve on zeotropes. Using bubble pressure for saturation temperature on R-407C / R-454C / R-455A overstates superheat by the glide value (11–22°F at a 40°F dew point). This calculator uses the dew curve automatically — verify any paper PT chart you reference shows both columns and use the dew column for SH.
- Sensor in the wrong place. Title 24 clamps it to the suction line near the outdoor unit's suction service valve[1]; follow your equipment's literature where it says otherwise.
- No insulation on the probe. An uninsulated clamp-on probe reads partly the line temperature and partly the ambient air temperature. Use closed-cell foam tape or insulation putty over the probe.
- Reading before steady state. Run the system at least 15 minutes before measuring[1]; American Standard asks for 20 minutes after start-up or any charge change[5]. Brief after-start spikes or transient values during defrost / cycle changes are not charging-decision data.
- Confusing total vs evaporator superheat. Total superheat, measured at the compressor, is higher than evaporator superheat because the suction line picks up heat on the way. Sporlan's worked example reads 10°F at the bulb and 30°F at the compressor inlet[7]. Title 24's fixed-orifice targets are read near the outdoor unit's service valve[1].
- PSIG vs PSIA mix-up. Service gauges read PSIG (gauge pressure above atmospheric); some refrigerant property software wants PSIA (absolute). PSIA = PSIG + 14.6959 at sea level. Mixing them up moves the R-410A saturation temperature by about 7°F at a 40°F coil.
When to use this calculator vs the others
- Superheat Calculator (this page) — suction-line measurement. Charge fixed-orifice systems; verify TXV operation; diagnose evaporator-side issues (undercharge, restriction, flooding).
- Subcooling Calculator — liquid-line measurement. Charge TXV / EEV systems; diagnose condenser-side issues (fouling, overcharge, low ambient airflow). Always pair with SH.
- Combined SH / SC / PT — both sides plus pattern-matching diagnostic banner. Use for full system commissioning or comprehensive diagnostic.
- PT Calculator — raw saturation lookup, no measurement input. Reference tool for cross-checking or comparing refrigerants.
- System Pressure Diagnostic — high-low pressure × high-low SH / SC pattern matcher. Use when you have all four values and want a quick fingerprint identification (undercharge, overcharge, restriction, airflow problem, compressor issue).
Primary sources behind the calculator and content
Saturation temperatures come from CoolProp 7.2.0 (50 refrigerants), CoolProp 8.0.0 (5) and Chemours’ charts for R-514A (1).
- [1]California Energy Commission, Reference Appendices for the 2025 Building Energy Efficiency Standards (Reference Appendix RA3.2), CEC-400-2025-010-AP. California Energy Commission. July 2025 (in effect January 1, 2026). https://www.energy.ca.gov/sites/default/files/2025-07/CEC-400-2025-010-AP.pdf (accessed October 19, 2026)
- [2]Sporlan Bulletin 10-9, Thermostatic Expansion Valves: Theory of Operation, Application, and Selection. Sporlan (Parker). March 2011. https://www.parker.com/content/dam/Parker-com/Literature/Sporlan/Sporlan-pdf-files/Sporlan-pdf-010/10-9.pdf (accessed October 19, 2026)
- [3]Sporlan Bulletin 10-11, Thermostatic Expansion Valves: Installation, Field Service, and Assembly. Sporlan (Parker). June 2011. https://www.parker.com/content/dam/Parker-com/Literature/Sporlan/Sporlan-pdf-files/Sporlan-pdf-010/10-11.pdf (accessed October 19, 2026)
- [4]Heatcraft Unit Coolers Installation and Operations Manual, H-IM-UC. Heatcraft Refrigeration Products. June 2026. https://heatcraftrpd.com/dA/372b2b9e1e/H-IM-UC.pdf (accessed October 19, 2026)
- [5]American Standard, Installation Instructions: Split System Air Conditioner & Heat Pump, 1.5–5 Tons, R410A, 14 SEER (©2020), section 14.2. American Standard (Trane Technologies). 2020. https://www.tranetechnologies.com/content/dam/common/oxbox/heat-pumps/pre-doe_14_seer_(j4hp4)/InstallationManual_J4HP4_14SEER.pdf (accessed October 19, 2026)
- [6]AHRI Standard 210/240-2023 (2020), Performance Rating of Unitary Air-conditioning and Air-source Heat Pump Equipment. AHRI. 2023 (2020). https://www.ahrinet.org/system/files/2023-09/AHRI%20Standard%20210.240-2023%20%282020%29.pdf (accessed October 19, 2026)
- [7]Sporlan Form 10-135, Using P-T Analysis As A Service Tool. Sporlan (Parker). 2013. https://www.parker.com/content/dam/Parker-com/Literature/Sporlan/Sporlan-pdf-files/Sporlan-pdf-Miscellanous/Form-10-135_52013.pdf (accessed October 19, 2026)
- [8]Copeland Discus K/L/S Series Semi-Hermetic Compressors: Application Guidelines (section 7.4), D6.3.4/0715-0716/E. Copeland. 2016. https://s1-live.copeland.com/documents/discus-k-l-s-series-semi-hermetic-compressors-application-guidelines-en-gb-4209402.pdf (accessed October 19, 2026)
- [9]Emerson Climate Technologies (Copeland) AE4-1400 R2, 1 to 5 Ton ZP*K6 R-410A Copeland Scroll Compressors. Copeland. February 2015. https://emerson.com/documents/commercial-residential/1-to-5-ton-zp-k6-r-410a-copeland-scroll-compressors-en-us-160824.pdf (accessed October 19, 2026)
- [10]Danfoss, Thermostatic Expansion Valve Troubleshooting, AC307572949567. Danfoss. 2017.12. https://assets.danfoss.com/documents/90976/AC307572949567en-010101.pdf (accessed October 19, 2026)
- [11]Sporlan Form 10-143, 12 Solutions for Fixing Common TEV Problems. Sporlan (Parker). 06/2012. https://www.parker.com/Literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20010/10-143.pdf (accessed October 19, 2026)
How to read your results
- Superheat (°F or °C)
- How many degrees the suction-line vapor sits above its saturation temperature; this is the vapor margin that keeps liquid out of the compressor. Compare it with your system's target: the chart value for a fixed orifice, or the manufacturer's figure for a TXV.
- Saturation temperature at suction pressure
- The temperature the entered suction pressure corresponds to on the PT chart; it is the baseline the superheat is measured from (superheat = line temp − this value). For zeotropic blends the tool reads the dew curve (labeled as such), which is the correct boundary for suction-line superheat; using the bubble curve would overstate superheat by the refrigerant's glide.
How to use this calculator
- Pick the refrigerant in the system. Defaults to R-410A.
- Read the suction-line pressure from the low-side manifold gauge; most service gauges read PSIG by default.
- Measure the suction-line temperature with a clamp-on probe on the suction line near the outdoor unit's service valve, insulated from the air, after the system has run at least 15 minutes[1].
- Enter both values. The calculator returns superheat in °F (or °C if you toggle the unit) plus a diagnostic banner.
- Compare against your equipment's target superheat (OEM charging chart, TXV spec, or the fixed-orifice charging-chart reference below).
Common errors
- Reading the discharge pressure instead of the suction pressure. The suction is the LOW side; discharge is the HIGH side.
- Probing the suction line without insulating: ambient air pulls the reading toward room temperature, inflating apparent superheat.
- On zeotropic blends, using the bubble pressure for saturation temperature overstates superheat by the temperature glide (11°F for R-407C, 14°F for R-454C, 22°F for R-455A). This calculator does dew-curve math automatically.
- Forgetting that fixed-orifice and TXV systems have very different target ranges.
- Reading SH before steady state. Run at least 15 minutes after start before reading[1].
Underlying math
Formula
Superheat (°F) = T_suction_line − T_sat(P_suction) T_sat is read off the DEW curve at the measured suction pressure for zeotropic blends. For pure refrigerants and azeotropes, bubble ≡ dew, so the curve choice is moot.
Source
Saturation temperatures come from CoolProp 7.2.0 (50 refrigerants), CoolProp 8.0.0 (5) and Chemours' charts for R-514A (1). Fixed-orifice targets: California Title 24 Table RA3.2-2[1]. TXV and refrigeration ranges: Sporlan Bulletins 10-9 and 10-11 and Heatcraft H-IM-UC[2][3][4].
Worked example
R-410A residential AC, 95°F outdoor, TXV metering: Suction pressure (gauge): 130 PSIG Suction-line temperature: 60°F Saturation temperature at 130 PSIG: 45°F (CoolProp 7.2.0) Superheat = 60 − 45 = 15°F Within the typical 8-15°F TXV target range and comfortably above the slugging threshold. For a fixed-orifice system, cross-check against the fixed-orifice charging chart for the specific indoor wet-bulb / outdoor dry-bulb combination.
Related tools
Subcooling Calculator
Companion to superheat on the liquid line. Together they pin down a system's charge state.
Combined PT / SH / SC
All three measurements on one form with pattern-matching diagnostic banner.
PT Calculator
Raw saturation-pressure lookup for any refrigerant.
System Diagnostic
Pattern matcher for high/low pressure × high/low SH/SC fingerprints.
Target Superheat Chart
Fixed-orifice target lookup by indoor WB × outdoor DB. Refrigerant-independent method.
R-410A Superheat Chart
Target matrix + R-410A saturation quick table for fixed-orifice residential AC.
R-22 Superheat Chart
Target matrix + R-22 saturation quick table for legacy fixed-orifice service.
High Suction Low Head
Diagnostic tree for the specific pattern where both pressures converge — internal leakage.
AC Low Side Pressure Too High
Diagnostic tree for suction above normal.
Low Suction Pressure
Broad diagnostic tree for suction below normal — undercharge, restriction, or airflow.
AC Compressor Short Cycling
Cycling patterns and their root causes on residential and automotive systems.
R-410A reference
Full PT chart, operating pressures, and lubricant guidance for the dominant residential AC refrigerant.
Frequently asked
›What is superheat?
Superheat is the temperature of refrigerant vapor above its saturation temperature at the same pressure. On a split system, Title 24 measures it on the suction line near the outdoor unit's service valve: suction-line temperature minus the saturation temperature at the suction pressure[1]. Positive superheat means the refrigerant has fully boiled; zero or negative superheat means liquid is reaching the compressor (slugging), which Copeland links to valve-plate and connecting-rod damage and to bearing wear from diluted oil[8][9].
›What is the target superheat for an HVAC system?
Depends on the metering device. Fixed-orifice systems: a target from 5 to 45°F, read from Title 24's chart of indoor wet-bulb and outdoor dry-bulb[1]. TXV systems: typically 8–12°F, up to 15°F on high-TD coils; the valve holds a nearly constant superheat[2][3]. Walk-in coolers: 6–8°F (Sporlan) or 6–10°F at a 10°F design TD (Heatcraft); walk-in freezers: 4–6°F (Sporlan)[2][4]. For heat pumps, American Standard approves checking the charge only in cooling mode[5]. Always cross-check against the manufacturer's service literature for the specific equipment[2].
›How do I measure superheat in the field?
Connect a manifold gauge to the suction service port and read the pressure in PSIG. Measure the suction-line temperature with a clamp-on probe on the suction line near the outdoor unit's service valve, insulated from the air, after the system has run at least 15 minutes[1]. Convert the suction pressure to saturation temperature using a PT chart for your refrigerant; use the dew curve for zeotropic blends. Subtract: superheat = T_line − T_sat. This calculator does the conversion and dew-curve selection automatically.
›What does low superheat indicate?
Low superheat means the evaporator is close to flooding. Sporlan lists a TXV that overfeeds and lost air movement from dirt or ice among the causes[11]; on a fixed-orifice system, compare with the chart target before adjusting the charge[1]. Liquid reaching the compressor damages it: Copeland lists valve-plate, piston and connecting-rod damage, and bearing wear from diluted oil[8][9]. Cross-check with subcooling and verify indoor airflow before adjusting charge.
›What does high superheat indicate?
High superheat means the evaporator is starved: above the chart target on a fixed-orifice system, or above the manufacturer's figure (Title 24's default limit is 25°F) on a TXV system[1]. A low charge raises superheat and lowers subcooling and evaporator pressure, and a liquid-line restriction such as a clogged filter-drier can starve the valve even with a proper charge[10]. Check subcooling first. Low subcooling alongside high superheat strongly suggests undercharge[10]. Verify indoor airflow and check the liquid line and filter-drier for a restriction[10] before adding refrigerant.
›Why does superheat math differ for zeotropic blends?
Zeotropic blends (R-407C, R-454C, R-455A, R-448A, R-449A) condense and evaporate across a temperature range at constant pressure. On the suction line the refrigerant has already passed through evaporation, so the relevant saturation boundary is the dew temperature, not the bubble temperature. This calculator uses the dew curve automatically for zeotropic blends. Using the bubble curve for R-407C would overstate superheat by approximately 11°F; for R-455A by approximately 22°F (bubble sits below dew at a given pressure, so subtracting it inflates the result).
›Is this the same as Total Superheat versus Evaporator Superheat?
This calculator computes superheat wherever you measure it; Title 24's fixed-orifice procedure measures on the suction line near the outdoor unit's service valve[1]. A TXV controls superheat at its bulb, at the evaporator outlet[2]; Title 24's fixed-orifice targets are read near the outdoor unit[1]. The distinction matters most on systems with long suction line sets exposed to warm spaces. Sporlan's worked example reads 10°F at the bulb and 30°F at the compressor inlet[7].
›Does this calculator work with R-1234yf and R-454B?
Yes. R-1234yf and R-454B are both in the calculator's list of 56 refrigerants.