Automatic Leak Detection Is Now Mandatory on Big Systems — Is Your Customer's Covered? (§ 84.108)

Most of the equipment you touch will never trigger this rule.

But some of it will — and if you're the contractor on a supermarket rack, a cold-storage warehouse, an ice rink, or an industrial process chiller, you need to know that the EPA now requires those systems to have an automatic leak detection (ALD) system bolted on and running. This isn't an optional upgrade or a "best practice." It's a federal mandate under 40 CFR § 84.108, and the systems that were already in the ground have a hard deadline coming: January 1, 2027.

Here's exactly who's covered, what an ALD system has to do to satisfy the rule, and — the part contractors actually ask about — what having one gets you out of.

Who Actually Has to Have One

The trap here is assuming "big system = covered." The rule is narrower than that, and the boundary matters.

Read that again, because the wording does real work:

It names two end uses: industrial process refrigeration and commercial refrigeration. Comfort cooling is not on the list. A 1,600-pound centrifugal chiller cooling an office tower is a comfort-cooling appliance — it does not fall under the § 84.108 ALD mandate, even though it's well over 1,500 pounds. The same 1,600 pounds in a supermarket's low-temp rack or a cold-storage system does. If you can't answer "is this comfort cooling or refrigeration?" for a given unit, that's the first question to settle.

The 1,500-pound line is the full charge of a single appliance. This is the same "full charge" figure you already determine for leak-rate math — the amount of refrigerant the appliance holds when operating at design conditions. It's not a facility total. A grocery store with three separate 700-pound systems has zero appliances over the ALD threshold; a single 1,800-pound rack next door has one.

GWP greater than 53 is the same substance test that gates all of Subpart C — the same one that pulls R-410A, R-404A, R-407A, and the rest of the HFC field into the 15-pound rule. If it's regulated for leak repair, it's regulated for ALD once you cross 1,500 pounds in the right end use.

Two Deadlines, Depending on When It Went In

The rule splits on install date, and both dates are already live or nearly so.

For the new-install case, this is already the rule of the land — every qualifying system you commission this year needs detection online within a month of startup. Bake it into the commissioning checklist so it isn't an afterthought that slips past day 30.

For the existing case, the runway looks generous until you count backwards. January 1, 2027 is roughly six months out. On a supermarket or cold-storage system, sourcing the right sensors, running wiring to the compressor room and case lines, integrating with the building's alarm or refrigeration controller, and getting it commissioned is not a same-week job — and you are not the only contractor whose customers all hit the same deadline. The shops that get burned here are the ones that treat "January 2027" as a January 2027 problem.

What Counts as an ALD System

The rule recognizes two fundamentally different ways to catch a leak, and lets you use either. Knowing which one a given install uses tells you what it has to be capable of.

Option 1 — Sense the refrigerant in the air

This is the sensor-in-the-room approach: fixed detectors watching the air near where leaks happen.

• Sensors must continuously monitor refrigerant concentration in the air near the compressor, evaporator, condenser, and other areas with high leak potential (§ 84.108(f)(1)).
• They must accurately detect a concentration of 10 parts per million of vapor (§ 84.108(f)(2)).
• They must alert the owner or operator at 100 parts per million (§ 84.108(f)(3)).

If a supplier is quoting you a "leak detector" that can't resolve down to 10 ppm and throw an alert at 100 ppm, it doesn't meet the rule — it's a shop-safety sniffer, not a compliant ALD sensor.

Option 2 — Monitor the appliance's own condition

This is the performance-monitoring approach: instead of sniffing air, the system watches the appliance's operating data (pressures, levels, run behavior) and infers loss.

• It must alert the owner or operator when measurements indicate a loss of 50 pounds of refrigerant, or 10 percent of the full charge — whichever is less (§ 84.108(g)).

On a 1,500-pound system, 10 percent is 150 pounds, so the 50-pound floor is what governs — it has to alarm at a 50-pound loss. On a 400-pound portion, 10 percent is 40 pounds, so 40 governs. "Whichever is less" always pulls the trigger to the tighter number.

What Having One Gets You Out Of — and What It Doesn't

This is the question every owner asks once they hear the price of installing detection on a big rack: what do I get for it?

The real payoff is inspection relief. Under Subpart C, once an appliance blows a leak rate you're on the hook for a follow-up inspection cadence — quarterly for systems 500 pounds and up, annually for smaller ones — that runs until the unit demonstrates a clean stretch (§ 84.106(g)). That's boots-on-the-roof labor, repeated, on every chronic system. (We walk through that whole cadence in the leak-rate-exceeded workflow post.)

So a properly maintained ALD system replaces the recurring manual inspection on the portion it watches. On a large system that would otherwise be climbing back onto a quarterly inspection treadmill, that's the whole economic argument for the sensors.

But read the fine print, because it's where contractors get tripped up:

It only covers the portion the ALD actually monitors. If your detection watches the machine room but not the far end of a distributed case line, and that appliance is found leaking above the applicable rate, § 84.108(h) says the remainder of the appliance stays subject to the inspection requirements. Partial coverage buys partial relief.

It does not touch anything else in the rule. ALD exempts you from the periodic inspection — full stop. It does not exempt the owner from:

• Calculating the leak rate every time refrigerant is added.
• The 30-day repair clock once a threshold is exceeded.
• The retrofit-or-retirement path, or the March 1 chronic-leaker report.
• Any of the recordkeeping the rest of Subpart C demands.

An ALD alarm, in fact, is often the event that starts those clocks. The detector tells you refrigerant is escaping; everything you already know about leak rate, repair deadlines, and documentation kicks in from there. The sensor doesn't make the compliance obligation go away — it just makes sure you find out in time to meet it.

The Records the ALD Itself Has to Generate

Installing the system creates its own recordkeeping line item. Under § 84.108(i), the owner or operator must keep, for at least three years:

1. Records of the installation of the ALD system.
2. Records of the annual audit and calibration.
3. Each date the ALD system triggered an alert.
4. The location of the leak(s) that caused the alarms.

That third and fourth item are the ones people forget. Every alarm is a dated, locatable event that has to live in the file for three years — the same three-year retention that governs the rest of your Subpart C records. If the EPA ever asks how a chronic system was being watched, "we had sensors" isn't the answer; the alert log is.

An ALD alarm doesn't end a compliance obligation. It's usually the event that starts one — and it has to be logged, dated, and located for three years.

One Note for Contractors Working in California

If your qualifying systems are in California, the federal 1,500-pound line is now the stricter trigger. California's CARB refrigerant management program sets its automatic leak detection threshold at 2,000 pounds, so a system in the 1,500–2,000-pound band that CARB left alone is now pulled in by the federal rule. You comply with the tighter of the two — which, on ALD, is federal. We cover the full state-versus-federal overlap in the state refrigerant rules post; the short version is that Subpart C has quietly become the floor everyone has to clear.

What to Do This Week

You don't need to solve this for every customer at once. You need to know where the exposure is:

Inventory your ≥1,500-pound refrigeration and process systems. Comfort-cooling chillers come off the list. Supermarket racks, cold-storage plants, ice rinks, and industrial process refrigeration stay on it. For each one, note the install date — that decides whether it's already-due (new) or January-1-2027-due (existing).

Calendar the 2027 deadline backwards. For every existing qualifying system, put January 1, 2027 on the schedule and work back from it for sensor lead time, wiring, controller integration, and commissioning. Six months disappears fast when every contractor is chasing the same date.

Spec the right detection, not the cheapest. The sensor has to detect 10 ppm and alarm at 100 ppm, or the condition-monitor has to alarm at the 50-pound-or-10% floor — and either way it needs an annual calibration plan, or the § 84.106(g)(4) inspection exemption evaporates.

Wire the alarm log into your records now. When the detection goes live, every alert becomes a three-year record with a date and a location. Decide where that lives before the first alarm, not after.

The contractor who gets ahead of this turns a looming deadline into a straightforward add-on sale with a clear compliance payoff for the customer. The one who waits is quoting the same job in December 2026 with no lead time and a room full of competitors doing the same.

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Automatic leak detection is mandatory now on the big systems — but the sensor is only half the job. The alarms it throws feed straight into the leak-rate, 30-day-repair, and recordkeeping machinery of Subpart C, and those are the parts an inspector actually audits.