Refrigerant Charge Calculator

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Factory Charge Only Covers So Much Line

Split-system air conditioners and heat pumps ship pre-charged with refrigerant for a standard line set length — typically 15 or 25 feet. Run a longer line between the outdoor and indoor units, as almost every real installation does, and additional refrigerant has to be added to make up the difference. This calculator applies the manufacturer factory-charge method to work out exactly how much.

The Formula

Extra Line Length = max(0, Actual Length − Included Length)
Additional Charge = Extra Length × Charge per Foot
Total Charge = Base Charge + Additional Charge

The base (factory) charge already accounts for the manufacturer's included line length. Only footage beyond that included length requires additional refrigerant, at the manufacturer-specified rate per foot for the line set diameter in use.

A Worked Example

54 oz factory charge, 15 ft included, 40 ft actual run, 0.6 oz/ft additional
StepValue
Extra Line Length (40 − 15)25 ft
Additional Charge (25 × 0.6)15.0 oz
Total Charge69.0 oz (4.313 lb)
Note: This uses the standard manufacturer factory-charge approach. Always verify against the specific unit's nameplate and installation manual, and confirm final charge with superheat/subcooling measurements rather than the calculated figure alone.

Where This Calculation Matters

  • New split-system installation — determining how much additional refrigerant to add before start-up, based on the actual line set run.
  • Line set replacement — recalculating required charge when a longer or shorter line set is installed during a repair.
  • Multi-story and long-run installations — outdoor units placed far from the indoor coil, common in retrofits, often exceed the factory-included length by a wide margin.
  • Pre-installation material planning — estimating refrigerant needs before a job to avoid a mid-installation supply run.

How to Use This Calculator

  1. Enter the Factory (Base) Charge in ounces, from the unit's nameplate.
  2. Enter the Line Length Included in the Base Charge, in feet.
  3. Enter the Actual Installed Line Length, in feet.
  4. Enter the Additional Charge per Foot, in oz/ft, from the manufacturer's specifications.
  5. Select Calculate to see the total refrigerant charge required.

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Confirm the system is sized correctly for the space before charging it, using the HVAC Load Calculator or Heat Pump Sizing Calculator.