How to calculate a refrigerant leak rate, with examples.

When you need a leak rate.

Under EPA’s Section 608 and AIM Act rules, a leak rate must be calculated every time refrigerant is added to a covered system: 15 lb or more of HFC, or 50 lb or more of an ozone-depleting refrigerant such as R-22. For commercial refrigeration, a result above 20% means the leak must be repaired within 30 days.

EPA allows two methods. Use one method consistently for all covered systems at a facility.

Method 1: annualizing.

The annualizing method projects the latest addition over a full year.

Worked example: annualizing.

A rack has a full charge of 1,200 lb. A technician adds 60 lb. The last addition to this rack was 90 days ago.

60 ÷ 1,200 = 0.05. Then 0.05 × 365 ÷ 90 = 0.203. The leak rate is 20.3%, above the 20% commercial refrigeration trigger. The leak must be repaired within 30 days.

Notice that a modest 60 lb top-up produces a failing leak rate because it came only three months after the last one. Frequent small additions add up quickly under this method.

Method 2: rolling average.

The rolling-average method looks back instead of projecting forward. Add up all the refrigerant added in the past 365 days, or since the last successful follow-up verification test if that was more recent. Divide by the full charge and multiply by 100.

Worked example: rolling average.

The same 1,200 lb rack received 45 lb eight months ago, 30 lb 90 days ago and 60 lb today: 135 lb in the past 365 days.

135 ÷ 1,200 × 100 = 11.3%. That is below the 20% trigger.

The same rack gives different answers under the two methods, which is why the method must be applied consistently and recorded.

The chronic-leak check.

Separately from the leak rate, add up everything added to each system during the calendar year. If the total reaches 125% of the full charge, the system is a chronically leaking appliance and must be reported to EPA by March 1 of the following year. For our 1,200 lb rack, that line is 1,500 lb.

Don’t just calculate it. See it coming.

A leak rate is calculated after the refrigerant is already gone. Continuous monitoring can flag a rack that is losing charge weeks before the next top-up, while the leak is smaller and the leak rate is still low.