Leak repair rules, leak rates and verification

Back at the shop after the chiller leak search, Dana pulled up the chiller's history on the screen. The seniors' residence chiller holds 210 lb of R-134a. The previous contractor had added 13 lb in February and 20 lb in early September. "Before we talk about the repair," Dana said, "tell me how fast it was leaking. That number decides how quickly we have to act, what we have to test and what we have to write down." Theo had never calculated a leak rate. By the end of the afternoon he could do it two ways, and he understood why the regulations care about it.

This lesson covers how leak rates are calculated, the rules that require leaks to be repaired, how repairs are verified, and what happens when a system cannot be repaired. It builds on the leak detection methods of Lesson 10.

Why leak rates matter

A leak rate expresses how fast a system loses refrigerant as a percentage of its full charge per year. It turns a series of top-ups into a single number that can be compared with a limit and tracked over time. A system with a large charge that loses a few pounds a year has a low leak rate; a small system that loses the same amount is leaking badly. Owners use leak rates to manage refrigerant budgets and to decide when to repair or replace equipment, and in the United States the leak repair rules are built on them.

The full charge is the amount of refrigerant the system needs to operate normally, not the amount it happens to hold today. It can be taken from the manufacturer's data, calculated from the sizes of the components and piping, determined by recording how much is needed to bring the system to normal operating conditions, or estimated by a combination of these. The full charge should be recorded so that every technician uses the same number.

Calculating a leak rate

Two methods are used. The annualizing method takes the amount just added and scales it to a year, based on the time since refrigerant was last added:

where d is the number of days since refrigerant was last added, or 365 if more than a year has passed. The rolling average method adds up all the refrigerant added over the past year, or since the last time all leaks were repaired and verified if that was less than a year ago, and divides by the full charge:

The two methods can give quite different answers for the same system. The annualizing method reacts quickly: a large addition after a short interval gives a high rate. The rolling average smooths over a year. Under the US rules an owner may choose either method for an appliance, but must use it consistently, with switching allowed only under set conditions.

# Leak rate by the annualizing and rolling average methods
from datetime import date

def annualizing(added, full, last_add, this_add):
    days = min((this_add - last_add).days, 365)
    return added / full * 365 / days * 100

def rolling(additions, full, on):
    total = sum(lb for d, lb in additions if 0 <= (on - d).days < 365)
    return total / full * 100

systems = {
    "seniors' residence chiller (comfort cooling, 10 %)": (210.0, 10, [(date(2026, 2, 10), 13.0), (date(2026, 9, 2), 20.0)]),
    "old grocery rack (commercial refrigeration, 20 %)": (100.0, 20, [(date(2025, 6, 1), 9.0), (date(2025, 11, 20), 7.5), (date(2026, 3, 5), 5.5)]),
}
for name, (full, limit, adds) in systems.items():
    for (d0, _), (d1, lb) in zip(adds, adds[1:]):
        a = annualizing(lb, full, d0, d1)
        r = rolling(adds, full, d1)
        flag = "OVER" if max(a, r) > limit else "under"
        print(f"{name}: {d1}  annualizing {a:5.1f} %  rolling {r:5.1f} %  -> {flag} {limit} %")

seniors' residence chiller (comfort cooling, 10 %): 2026-09-02  annualizing  17.0 %  rolling  15.7 %  -> OVER 10 %
old grocery rack (commercial refrigeration, 20 %): 2025-11-20  annualizing  15.9 %  rolling  16.5 %  -> under 20 %
old grocery rack (commercial refrigeration, 20 %): 2026-03-05  annualizing  19.1 %  rolling  22.0 %  -> OVER 20 %

The grocery rack's history shows the two methods disagreeing. Its first two additions give annualized rates near the 20 percent line, while its rolling average climbs as additions accumulate within a year. Owners who track both see the trend early.

When leaks must be repaired

Under the US rules, an owner whose equipment is covered by leak repair must calculate the leak rate each time refrigerant is added, with limited exceptions. If the rate exceeds the threshold for its type, 30 percent for industrial process refrigeration, 20 percent for commercial refrigeration, or 10 percent for comfort cooling and other equipment, the owner must have the leaks identified and repaired within 30 days of the addition, or 120 days where an industrial process shutdown is needed. Repairs must bring the leak rate below the threshold. Covered equipment is equipment with 50 pounds or more of ozone-depleting refrigerant under Section 608, and, from January 1, 2026, equipment with 15 pounds or more of an HFC or substitute with a GWP above 53 under the AIM Act rule, except residential and light commercial air conditioning and heat pumps.

Time limits can be suspended if the system or the leaking component is isolated and evacuated, and extensions are available in set circumstances, such as when a part is unavailable or the repair would violate other safety rules. The owner must document the reasons and, in many cases, notify EPA. Federal, military and some industrial facilities have additional extension provisions.

Repairing leaks properly

A good repair fixes the cause, not just the symptom. Tightening a leaking flare may stop the leak for a month; replacing it with a brazed joint, or remaking it properly with the right flare tool and torque, and supporting the tubing so it does not vibrate, stops it for good. The repair options depend on the leak:

• Mechanical joints: remake flares with proper tools and torque, replace worn fittings, and where suitable replace flare connections with brazed joints.
• Access fittings and valves: replace leaking cores, install and tighten caps with their seals, repack or replace valve stems, and replace relief valves that weep.
• Vibration damage: replace damaged tubing, add clamps and isolators, and correct rubbing points.
• Corroded coils: repair is rarely lasting; replace the coil, and look for the cause, such as chemicals in the space for formicary corrosion.
• Brazed joints: recover, open and rebraze with nitrogen flowing, rather than adding braze over a leaking joint.

Sealants that are added into the refrigerant circuit to stop leaks are controversial. Some equipment manufacturers prohibit them, they can damage recovery machines and contaminate recovered refrigerant, and they hide the leak instead of fixing it. Northfield does not use them, and many reclaimers will reject refrigerant that contains them.

Verification tests

A repair is not finished until it has been shown to work. Verification is done in two stages.

• An initial verification test, made after the repair and before the system is fully recharged, or as soon as it is safe to test, confirms that the repaired joint does not leak. It may be a bubble test or electronic detector test of the repaired joint under nitrogen or refrigerant pressure, or a standing pressure test of the repaired section.
• A follow-up verification test, made after the system has returned to normal operating conditions, confirms that the repair holds under real temperatures, pressures and vibration. Under the US rules, this follow-up must be done within 10 days of a successful initial test or of the system returning to normal operation.

If either test shows the repair failed, more repairs are made and the tests repeated. Every test is recorded with the date, method, result and the technician's name. Theo's follow-up visit to the chiller, a week after the repair, found no leaks at either repaired joint or anywhere else, and that visit closed the repair record.

When repair is not the answer

Some systems cannot be made tight at a reasonable cost: old equipment with widespread corrosion, systems that have been repaired many times, or equipment for which parts no longer exist. Under the US rules, if an owner decides to retrofit or retire covered equipment instead of repairing it, or if the leak rate is still above the threshold after repair attempts, the owner must create a retrofit or retirement plan within 30 days and generally complete it within one year. Equipment covered by the AIM Act rule that leaks 125 percent or more of its full charge in a calendar year is chronically leaking, and the owner must report it to EPA by March 1 of the following year. The decision is often easier than it seems: a system leaking a large share of its charge each year wastes refrigerant, energy and money.

Large systems increasingly use automatic leak detection: fixed sensors in machinery rooms and refrigerated spaces, or monitoring of receiver levels, that alert the owner to leaks between service visits. Under the AIM Act rule, new commercial refrigeration and industrial process refrigeration systems with 1,500 pounds or more of HFC refrigerant installed from 2026 must have automatic leak detection, and similar existing systems installed from 2017 must add it by 2027; it can also be used in place of periodic leak inspections.

After the repair: watching the system

A system that has exceeded its leak rate threshold must also be inspected for leaks afterwards. Under the AIM Act rule, commercial refrigeration and industrial process refrigeration systems with 500 pounds or more must be inspected quarterly until they have shown four consecutive quarters below the threshold; smaller covered systems, and comfort cooling and other systems, must be inspected annually until they have shown a year below the threshold. Automatic leak detection can take the place of these inspections where it is installed. Northfield books the chiller's annual inspection with its seasonal start-up and records the result in the owner's register.

Explaining leak rates to owners is part of the job. A facility manager may see only the cost of a repair. Showing the refrigerant added over the past year, its cost at current prices, its carbon dioxide equivalent, and the efficiency lost while the system ran short of charge usually makes the case for a proper repair, or for replacement, more clearly than any regulation.