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The liquid line as installed, measured along the route rather than point to point.
The liquid line is the one that matters for charge, because it is the only part of the circuit that runs full of liquid. Its length, not the suction line's and not the pair's, is what the manufacturer's rate is written against.
The line length already covered by the factory charge, from the model's own document.
Commonly stated as 25 ft (7.62 m) on North American residential split systems and as 5, 7 or 10 m on many ducted and multi-split products. Some units ship charged for the outdoor section only, in which case this figure is zero and the whole run is added.
The refrigerant mass the manufacturer adds for each unit of liquid line beyond the standard length.
Printed in the installation instructions against the liquid line size. The default here corresponds to 0.6 oz per foot (0.0375 lb/ft, 0.0558 kg/m), which is of the order published for a 3/8 in liquid line — it is a placeholder for the shape of the answer, not a specification, and the model's own figure replaces it.
The bore of the liquid line, used to report the volume of the extra run as a cross-check.
Subtract twice the wall thickness from the outside diameter: 3/8 in OD with a 0.030 in wall gives a 0.315 in bore, about 8 mm. The volume this produces is a sanity check on the charge rate entered — multiply it by the refrigerant's liquid density at line temperature and the two should be close.
Additional charge to weigh in
1.537 lb
- Line length beyond the factory-charge standard
- 41 ft
- Internal volume of the run beyond standard
- 37.13 in³
- Charge rate applied
- 0.04 lb/ft
They open the calculator with your figures already in it
Refrigerant Line Length Charge Adjustment Calculator: 1.54 lb — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Manufacturer installation instructions: additional charge = (measured liquid line length − the standard line length the unit ships charged for) × the published charge rate per unit of liquid line. Both the standard length and the rate are model-specific and are entered here from that document
- AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment — split systems are rated with a standard length of interconnecting tubing, which is why a longer field run needs charge added rather than being an equivalent installation
- The default charge rate and standard length are PLACEHOLDERS of the right order, not published values. Replace both with the figures printed for the model being installed
Inputs used
- Measured Liquid Line Length
- 66 ft
- Standard Line Length the Model Ships Charged For
- 25 ft
- Published Charge Rate per Unit of Liquid Line
- 0.04 lb/ft
- Liquid Line Inside Diameter
- 0.31 in
Intermediate steps
- Line length beyond the factory-charge standard
- 41 ft
- Internal volume of the run beyond standard
- 37.13 in³
- Charge rate applied
- 0.04 lb/ft
What this calculation does not cover
- This is a weigh-in figure, not a commissioning verdict. Subcooling and superheat measured at operating conditions are what confirm the charge is right, and they can disagree with the arithmetic when the metering device, the line insulation or the indoor airflow is not as assumed.
- Assumes the liquid line runs full of liquid. A line with a long lift, a sight glass showing flash gas, or a badly insulated run in a hot roof space will not.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0
Regulatory standards & verification citations3
- Manufacturer installation instructions: additional charge = (measured liquid line length − the standard line length the unit ships charged for) × the published charge rate per unit of liquid line. Both the standard length and the rate are model-specific and are entered here from that document
- AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment — split systems are rated with a standard length of interconnecting tubing, which is why a longer field run needs charge added rather than being an equivalent installation
- The default charge rate and standard length are PLACEHOLDERS of the right order, not published values. Replace both with the figures printed for the model being installed
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