Why is the fill limit 80 percent?

Liquid refrigerant expands as it warms. DOT 49 CFR 173.301 requires that a refrigerant cylinder hold no more than 80 percent of its water capacity by weight at 70 degrees Fahrenheit, leaving a vapour cushion so the cylinder does not go hydrostatically solid and rupture on a hot day.

How do I find the net refrigerant already in the cylinder?

Subtract the stamped tare weight, marked TW on the cylinder, from the current reading on your scale. The difference is the weight of refrigerant present. Always use a calibrated refrigerant scale rather than estimating from pressure.

What is the rated refrigerant capacity I should enter?

Enter the maximum refrigerant the cylinder may legally hold, which is the 80 percent number. Many recovery cylinders are sold by this figure, for example a 50 pound tank that is rated to hold about 47 pounds of R-410A. Check the cylinder label or the manufacturer's data.

What happens if the charge will not fit?

The tool warns you and you must use a second cylinder. Forcing more refrigerant into a tank already near 80 percent is both unsafe and a violation. Recovery into an overfilled cylinder can cause it to become liquid-full and burst.

Does the refrigerant type change the result?

The 80 percent weight rule applies to all refrigerants, but each one has a different density, so a given cylinder holds a different weight of R-22 than of R-410A. Always match the cylinder's labeled rated capacity to the refrigerant you are recovering and never mix refrigerants in one cylinder.

Refrigerant Recovery Cylinder Capacity Calculator

Technicians recovering refrigerant on EPA Section 608 jobs must never overfill a recovery cylinder. Liquid refrigerant expands sharply with temperature, and a cylinder filled past 80 percent of its capacity can become liquid-full and rupture. This tool checks how much refrigerant is already in a cylinder and whether the next system charge will fit safely.

How it works

The net refrigerant currently in the cylinder is the scale reading minus the stamped tare weight:

net = scale weight - tare (TW)

The fill percentage and remaining room are measured against the cylinder’s rated refrigerant capacity, which is the 80 percent number:

fill %     = net / rated capacity x 100
remaining  = rated capacity - net

To check whether a recovery will fit, the tool adds the system charge to the current net and compares against the rated capacity. If the total exceeds it, you must use another cylinder.

Safety notes

The 80 percent limit comes from DOT 49 CFR 173.301 and exists to leave a vapour cushion for thermal expansion. Always use a calibrated scale, confirm the cylinder is within its hydrostatic test date, and never mix refrigerants or put refrigerant into a cylinder labeled for a different service. When in doubt, stop and use a fresh, empty, in-date recovery cylinder.