Refrigerant Charge Calculator (Line Set Length)
The factory charge in a new condenser covers a set length of line, usually 15 feet. Enter the length your line set actually runs, the liquid line size and the factory charge from the data plate, and get the refrigerant to add or remove in ounces and the total charge to weigh in.
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How it works
Adjustment (oz) = (actual length − base length) × ounces per foot. A positive result is refrigerant to add; a negative one is refrigerant the manufacturer may tell you to remove. Total charge = factory charge + adjustment, which is the number to set on the scale.
The per-foot value depends on the liquid line diameter because almost all of the extra refrigerant sits in the liquid line; the suction line carries vapor and adds very little. Typical R-410A values are 0.2 oz per ft for 1/4 in., 0.4 for 5/16 in., 0.6 for 3/8 in. and 1.2 for 1/2 in. liquid line, but manufacturers publish their own tables and they vary, so enter the manual's figure when you have it. R-454B and R-32 equipment uses different, generally lower, per-foot values.
Weighing in gets you close. Finish the job by checking subcooling on a TXV or EEV system or superheat on a fixed-orifice system against the charging chart on the unit, with the system at steady state.
Worked example
A condenser with a 7 lb 8 oz factory charge covering 15 ft, installed on a 40 ft line set with 3/8 in. liquid line: 25 extra feet × 0.6 oz = 15 oz to add. The factory charge is 120 oz, so the total charge to weigh in is 135 oz, or 8 lb 7 oz.
Frequently asked questions
Do I measure the suction line or the liquid line?
Use the one-way length of the line set; the liquid and suction lines run together. The per-foot value is chosen by the liquid line diameter because that is where the added refrigerant sits.
What if the line set is shorter than the factory allowance?
Some manufacturers tell you to remove the difference, others say to leave the factory charge and let subcooling be the guide. Follow the installation manual for the unit.
Does this work for R-454B or R-32?
The math is the same, but the ounces per foot are different because those refrigerants have a lower liquid density. Enter the per-foot value from the manual instead of the R-410A defaults.
Does elevation between the condenser and the coil matter?
Not for the charge. For long vertical rises the manual may call for oil to be added and for traps in the suction line; check the line-set limits before you run it.
Can I just charge by subcooling and skip the math?
You can, but weighing in the calculated charge first gets you to the right neighborhood quickly and avoids overcharging while the system is still settling. Subcooling or superheat is the final check either way.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.