The A2L numbers California just fixed — and your heat-pump plan check

Here's the thing: the refrigerant in a heat pump you permit today is almost certainly A2L — mildly flammable. That's not a fringe case anymore. It's the mainstream. And in January 2026, California corrected the two numbers in the Mechanical Code that decide how much of that refrigerant you can put in a room, and when a detector has to trip.

Why your heat pumps went A2L

Federal HFC phasedown did this, not California. Under the AIM Act, EPA's Technology Transitions program set a 700 global-warming-potential (GWP) limit for most new comfort-cooling equipment. R-410A — the old standby — sits well above that line, so manufacturers moved residential and light-commercial air conditioners and heat pumps to lower-GWP blends. The two that won the market, R-454B and R-32, are both classified A2L.

A2L means lower toxicity and lower flammability — but flammable. Which is exactly why the Mechanical Code's refrigerant tables suddenly matter on jobs that never used to think about them.

What Table 1102.3 actually is

CMC Table 1102.3 is the master refrigerant table. For every refrigerant it lists the safety group, the Occupational Exposure Limit (OEL) in ppm, the Refrigerant Concentration Limit (RCL), and the Lower Flammability Limit (LFL) — the last two in pounds per 1,000 cubic feet (lb/Mcf).

Section 1103.1.1 treats A2L as its own distinct safety group, separate from A1 and A2. So R-454B and R-32 don't inherit the old A1 rules your office may run on muscle memory. They get the A2L path — and that path is driven by the RCL and LFL numbers in this table.

Verified against the live CMC Chapter 11 text: Section 1104.2 ties the maximum refrigerant charge in a high-probability system directly to "the amounts shown in Table 1102.3," and §1106.11.9 requires machinery-room detector set points "in accordance with Table 1102.3." The table is load-bearing, not reference trivia.

What the errata changed

The January 2026 CMC errata — effective and enforceable January 1, 2026 — revised the RCL and LFL values for the Safety Group A2L blends, R-444A through R-455A, to correct errors carried in from 2019 ASHRAE Standard 34 and its addenda, aligning the table with the IAPMO TIA (UMC 003-24). This correction was flagged as safety-critical — not filed under housekeeping — and it's easy to see why: these aren't editorial typos in a preface. They're the safety limits on a flammable gas.

If a designer pulled an RCL or LFL off the first printing of the 2025 table, the number on the plans may be the uncorrected one. The exact corrected figures live in the errata packet itself — pull them from the source below rather than from any earlier copy.

The two numbers do real work

This is the part to internalize, because RCL and LFL aren't trivia. They feed calculations you sign off on:

• Maximum charge per occupied space (§1104.2). The refrigerant in a complete discharge from one independent circuit of a high-probability system shall not exceed the RCL amount in Table 1102.3, measured against the volume of the occupied space. Get the RCL wrong and the largest legal charge for that room is wrong.
• Detector set points (§1106.2.5 and §1106.11.9). Machinery-room refrigerant detectors must alarm and start ventilation at a set point not more than the OEL, and for A2L the detector set point is also held not more than the RCL — both read straight from Table 1102.3.
• The de-energize trip (§1106.11.6.2, §1107.1.7.2). Detection above 25 percent of the LFL must automatically de-energize compressors, pumps, and normally-closed automatic refrigerant valves. That trip point is a fraction of the LFL number in the table.
• The electrical break (§1107.1.7). An A2L machinery room can avoid Class I, Division 2 hazardous-location electrical classification only if mechanical ventilation and that LFL-based detection are in place. The relief depends on the same numbers.

So one corrected row can move a maximum-charge calc, a detector set point, and a ventilation trip — all at once.

What to check Monday morning

Pull the corrected Table 1102.3 from the 2025 CMC errata packet, find the A2L blend on the job — most commonly R-454B — and re-run two things against the corrected RCL and LFL: the maximum-charge-per-space calculation in §1104.2, and the detector and ventilation set points for any required machinery room. If the plans cite a value that doesn't match the corrected table, that's your correction. As always, confirm the governing numbers with your local authority having jurisdiction; this is a plan-check pointer, not legal advice.

What CrossBeam does with it

CrossBeam reviews refrigerant and machinery-room submittals against the current Mechanical Code — Table 1102.3 as corrected by the January 2026 errata, not the first printing. So an A2L charge calculation or detector set point is measured against the values that are actually enforceable today.