Target Superheat Calculator — Free Online Calculator
Fixed-orifice (piston) air conditioners are charged to a target superheat that changes with indoor humidity and outdoor temperature. Enter the indoor wet-bulb and outdoor dry-bulb readings and this tool returns the chart target — so you know exactly what superheat to aim for before adding or removing refrigerant.
Have measured superheat already? Compare it with the Superheat Calculator — or screen airflow first with the Delta T Calculator.
Enter wet-bulb and dry-bulb temperatures
Return-air wet-bulb with system running
Ambient at the condenser
Target superheat
Chart range
5–25°F
Metering type
Fixed orifice
Charging note
Charge a fixed-orifice (piston) system to this target superheat at the outdoor conditions shown.
See the breakdown
Chart approximation only — always follow the manufacturer's charging chart for your refrigerant type and verify airflow before adjusting charge.
Target superheat quick reference
Common outdoor dry-bulb (85°F) at varying indoor wet-bulb readings.
| Indoor wet-bulb | Outdoor dry-bulb | Target superheat |
|---|---|---|
| 58°F | 85°F | 5°F (chart min) |
| 62°F | 85°F | 10.5°F |
| 64°F | 85°F | 13.5°F |
| 62°F | 95°F | 5.5°F |
| 64°F | 75°F | 18.5°F |
Sources & standards: HVAC School — superheat charging procedures · EPA Section 608 refrigerant handling · Manufacturer fixed-orifice charging charts (R-410A / R-22) · ACCA Manual S equipment selection.
The formula, explained in plain English
Manufacturer charging charts map indoor wet-bulb and outdoor dry-bulb to a target superheat. This calculator uses the standard linear approximation those charts follow.
Why wet-bulb, not dry-bulb indoors?
Indoor moisture load changes how much refrigerant the evaporator needs. Wet-bulb captures both temperature and humidity in one number the chart can use.
Fixed orifice only
TXV systems self-regulate flow — charge them by subcooling at the condenser, not superheat at the evaporator.
Confirm airflow first
Wrong airflow makes any superheat target meaningless. Check filter, blower speed, and static pressure before adjusting refrigerant.
Let the system stabilize
Take readings after 10–15 minutes of continuous run time with a clean filter and all supply registers open.
Worked examples
Three common field scenarios for piston-metered systems.
Typical summer day — 62°F WB, 85°F DB
Result: charge to 10.5°F superheat — a common mid-summer target for moderate humidity.
Hot afternoon — 64°F WB, 95°F DB
Result: high outdoor temperature drives the target down — expect a lower superheat on very hot days.
Mild day — 64°F WB, 75°F DB
Result: cooler outdoor air raises the target — don't chase a low superheat number on a mild day.
Frequently asked questions
Common questions about target superheat and fixed-orifice charging.
What is target superheat?
Target superheat is the superheat you should charge a fixed-orifice (piston) system to at a given set of indoor and outdoor conditions. It comes from the manufacturer's charging chart — a table keyed to indoor wet-bulb and outdoor dry-bulb temperatures.
What is the target superheat formula?
This calculator uses the common chart approximation: target superheat = ((3 × indoor wet-bulb °F) − 80 − outdoor dry-bulb °F) ÷ 2, clamped to 5–25°F. At 62°F WB and 85°F DB that gives 10.5°F.
When do I use target superheat vs. subcooling?
Use target superheat for fixed-orifice (piston) metering devices. TXV systems are charged by subcooling at the condenser, not superheat at the evaporator. If you're not sure which device you have, check the indoor coil — a TXV has an external sensing bulb on the suction line.
What wet-bulb and dry-bulb should I enter?
Enter the indoor wet-bulb (return-air moisture level — use a psychrometer or digital hygrometer with wet-bulb mode) and the outdoor dry-bulb (ambient air temperature at the condenser). Both readings should be stable with the system running.
Why is the result clamped to 5–25°F?
Manufacturer charging charts typically cap targets between 5°F and 25°F. Values outside that range usually mean the outdoor temperature is extreme or a probe reading is off — re-check before adding or removing refrigerant.
Does target superheat work for heat pumps?
The same piston-metering logic applies in cooling mode on a heat pump with a fixed orifice. In heating mode, charge verification follows the heat-mode manufacturer chart — use the Heat Pump Sizing Calculator to confirm system capacity first.
How do I measure actual superheat?
Actual superheat = suction line temperature minus saturation temperature at the same pressure. Use the Superheat Calculator to compare your measured value against this target.
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