Why add charge per foot of line?

Manufacturers pre-charge the outdoor unit for a standard line length, often 15 or 25 feet. Each extra foot of liquid line holds more refrigerant, so installers add a per-foot amount based on the liquid-line diameter. The vapor line holds very little liquid and is usually ignored.

How much refrigerant per foot of liquid line?

It depends on liquid-line diameter and refrigerant density. Common figures are about 0.6 ounces per foot for 3/8-inch line and 0.4 ounces per foot for 1/4-inch, with larger 1/2-inch lines around 1.2 ounces per foot. Always confirm against the equipment installation manual.

Does line length beyond the pre-charge subtract or add?

You add charge only for length beyond the manufacturer's included pre-charge length. If the actual line is shorter than the included length, some manufacturers have you remove charge, though many simply leave the factory charge in place for short runs.

What is the receiver and why add for it?

A receiver is a vessel that stores liquid refrigerant on systems with variable charge, such as those with head-pressure control. Its holding volume must be filled, so its rated charge is added on top of the line and coil charges for a complete system charge.

Should I still verify by superheat or subcooling?

Yes. This estimate gets you close for pre-charging or a starting weight, but final charge must be trimmed by the manufacturer's method, typically subcooling for TXV systems or superheat for fixed-orifice systems, under stable operating conditions.

Refrigerant System Charge Weight Calculator

When a line set runs longer than the manufacturer’s standard pre-charge length, the system needs extra refrigerant for the additional liquid-line volume plus any field-added components. This calculator sums the per-foot line charge and component adders onto the factory nameplate charge to give a starting total for pre-charging a new installation.

How it works

Total charge is the factory charge plus field additions:

line charge   = max(line length − included length, 0) × oz-per-foot
total charge  = factory nameplate charge
               + line charge
               + component adders (receiver, extra coil, etc.)

The per-foot figure depends on the liquid-line diameter and the refrigerant’s liquid density — larger lines and denser refrigerants hold more per foot. Only the liquid line is counted; the suction (vapor) line holds negligible liquid.

Example and tips

A condenser pre-charged for 25 ft with 6 lb (96 oz) of R-410A, connected by a 60 ft run of 3/8-inch liquid line at about 0.6 oz/ft, needs roughly 21 extra ounces for the 35 ft beyond the pre-charge — about 117 oz, or 7.3 lb total, before any receiver adder. Treat this as a pre-charge starting point, then trim to the manufacturer’s target subcooling or superheat once the system is running and stable.