What Is the Refrigerant Charge Calculator?
This tool estimates the total refrigerant charge for a split-system HVAC unit or heat pump. Manufacturers ship condensing units pre-charged for a standard line set length (often 15 or 25 ft). When the installed liquid line is longer, additional refrigerant must be added based on a per-foot rate from the equipment data plate. This calculator adds the factory base charge, the line-set adjustment, and any other corrections, then reports the result in ounces, pounds, and grams.
How to Use It
Enter the liquid line length in feet, the manufacturer charge-per-foot rate (commonly \(0.6\,\text{oz/ft}\) for 3/8" liquid line), the factory base charge if you want a complete total, and any other adjustment. The base charge and rate come from the unit nameplate or installation manual — always defer to those numbers.
The Formula
The total charge is:
$$Q_{total} = Q_{base} + (L \times r) + Q_{adj}$$where \(Q_{base}\) = factory base charge in oz, \(L\) = liquid line length in ft, \(r\) = charge per foot in oz/ft, and \(Q_{adj}\) = any other adjustment in oz. Conversions use \(Q_{lb} = Q_{oz}/16\) and \(Q_{g} = Q_{oz}\times 28.3495\).
Worked Example
A unit ships with a \(64\,\text{oz}\) base charge and the data plate specifies adding \(0.6\,\text{oz/ft}\) beyond the standard set. For a \(25\,\text{ft}\) line:
$$Q_{total} = 64 + (25 \times 0.6) + 0 = 79\,\text{oz}$$That equals \(79 / 16 = 4.94\,\text{lb}\) or about \(2240\,\text{g}\).
FAQ
What charge-per-foot value should I use? Use the value from the manufacturer installation manual. A typical figure is \(0.6\,\text{oz/ft}\) for a 3/8" liquid line, but it varies by line diameter and refrigerant.
Do I subtract for shorter line sets? Some manuals require removing refrigerant when the line is shorter than the factory-charged length. Enter a negative value in "Other Adjustment" to model that.
Is this a substitute for weighing in charge? No. This is an estimate. Always verify with a scale, subcooling, and superheat readings per the manufacturer procedure.
