Target Superheat Calculator

Target superheat is the superheat a fixed-orifice (piston or capillary-tube) air conditioner should read for the current operating load. It is set by two things: the indoor return-air wet-bulb temperature and the outdoor dry-bulb temperature entering the condenser. You add or recover refrigerant until the measured superheat matches the target. It applies to fixed-orifice metering only; TXV and EXV systems are charged by subcooling, not target superheat.

Target superheat is read from a charging chart indexed by indoor return-air wet-bulb and outdoor dry-bulb, not from a formula you keep in your head. The reverse-engineered field shortcut is [(3 x indoor wet-bulb) - 80 - outdoor dry-bulb] / 2, but it drifts up to about 7 degrees at the corners, so a chart is more accurate. This calculator interpolates the California Title 24 CEC RA3.2-2 target superheat table. Example: at 66F indoor wet-bulb and 90F outdoor dry-bulb, target superheat is about 13F.

Target superheat does not depend on the refrigerant. It is set by the load (indoor wet-bulb and outdoor dry-bulb), so the target for R-410A, R-454B, R-22, or R-32 on a fixed orifice is the same at the same conditions. What changes per refrigerant is how you read the measured superheat, because saturated suction temperature comes from that refrigerant's pressure-temperature chart. A chart labeled 410A target superheat is really the same load-based table with an R-410A PT scale attached.

There is no single good number: target superheat ranges from about 5F on a hot, dry day into the low 30s in mild, humid conditions with a high indoor wet-bulb, as the chart on this page shows. It rises as indoor wet-bulb rises (more latent load) and falls as outdoor dry-bulb rises. That is why a fixed-orifice system charged to a flat number like 12F is often wrong for the conditions. Charge to the chart target for the wet-bulb and dry-bulb you actually measure.

Actual (measured) superheat is what the system is doing right now: suction line temperature minus the saturated suction temperature from the refrigerant PT chart. Target superheat is what it should be doing for the current load. You compare the two: if measured superheat is more than about 5F above target the charge is low (add refrigerant after confirming airflow); if it is more than 5F below target the system is overcharged (recover).

No. A thermostatic or electronic expansion valve actively holds superheat near a fixed value on its own, so superheat tells you almost nothing about the charge on a TXV or EXV system. Charge those by subcooling instead. Target superheat is the charging method for fixed-orifice metering (pistons and capillary tubes), where superheat floats with the charge and the load.

As you add refrigerant the evaporator gets colder and pulls more moisture out of the indoor air, so the indoor return-air wet-bulb drops. A lower wet-bulb means a lower target superheat. Re-measure the wet-bulb and re-read the target after each addition rather than charging to the first number you looked up, or you will end up overcharged.

When the outdoor dry-bulb is high and the indoor wet-bulb is low, evaporator load is too low to set a charge by superheat. The CEC RA3.2-2 table stops giving a value because the target would fall below 5F, that close to floodback. Manufacturers draw the same line and some draw it wider: Goodman IOG-4048C dashes those cells and says do not attempt to check or charge the unit by the superheat method there, and to weigh the charge in instead. This calculator refuses in both cases rather than printing a low target you would chase by adding refrigerant. Weigh in to the nameplate, or return when conditions are closer to design.

Target values come from the California Energy Commission Title 24 Reference Appendix RA3, Table RA3.2-2, the state HERS charging reference. Cells are machine-parsed from the CEC's published Reference Appendices rather than hand-typed, and the shipped table is spliced from two printings (the 2019 appendices for the milder outdoor rows, the 2022 for the hot ones) and re-checked against the 2025 edition. Those are all one publisher, so agreement between them catches a transcription slip and is not an independent confirmation of the values. For an outside check, 168 of this table's 1054 cells were compared against manufacturer piston charging grids on 2026-08-04, which is about a sixth of it, and the rest carry no manufacturer check at all. ICP's R-410A air-conditioner grid (421 01 5103 00, Figure 12) agrees on all 115 cells it shares with this table, a mean of 0.08F and never more than 1F apart. Goodman's grid (IOG-4048C) does not: across the 53 cells it shares, this table runs a mean 4.77F and a worst 10F ABOVE Goodman's, and 15 of those 53 cells are further apart than the whole plus or minus 5F band a fixed-orifice charge is graded against. The gap is not flat: it widens from about 3F at mild outdoor temperatures to about 8F at 100F and above, so it is worst in the hot humid weather when most charging calls happen. Do not read the ICP agreement as proof this table is right. Agreement shows two publishers print the same targets, and both may inherit one lineage; on these cells the CEC and ICP grids both track the classic trade shortcut closely while Goodman's does not, so Goodman may be the genuinely independent chart here rather than the outlier. The two manufacturer grids share no cell directly, since ICP publishes even wet-bulb columns and Goodman odd ones, though that rests on reading one ambiguous ICP column label as 66 rather than 67, a reading confirmed by interpolating its neighbours rather than by fitting it to this table. Interpolating ICP's own grid onto Goodman's columns reproduces the same 4.77F gap with this table nowhere in the path, so the disagreement is between the manufacturers and is not an artifact of ours. The direction matters in the field: this table asks for MORE superheat than Goodman's, and charging to a higher superheat target leaves LESS refrigerant in the system. So on a Goodman piston unit charged exactly to Goodman's own chart, this tool can still read low and call for recovery. Where the manufacturer publishes a charging chart for the exact unit in front of you, that chart governs and this one does not. The CEC prints one decimal; this calculator rounds to whole degrees, half up, because the trade charges to whole-degree targets. The fixed-metering superheat pass tolerance is plus or minus 5F of the target per Table RA3.2-1.