ASHRAE Standard 15 classifies refrigerants on two axes: toxicity (A = lower toxicity, B = higher toxicity) and flammability (1 = no flame propagation, 2L = lower flammability, 2 = flammable, 3 = higher flammability). The class determines charge limits, ventilation, and install conditions. Here is what each class means and what code in Florida requires.
Toxicity: A or B. Based on Occupational Exposure Limit (OEL) and chronic toxicity data. A is OEL ≥ 400 ppm. B is OEL < 400 ppm. Most common refrigerants are A.
Flammability: 1, 2L, 2, or 3. Based on Lower Flammability Limit (LFL), heat of combustion, and burning velocity.
The two letter combine into a class: A1 (low tox, no flame), A2L (low tox, lower flammability), A2 (low tox, flammable), A3 (low tox, higher flammability), B1 / B2L / B2 / B3 likewise.
R-22, R-410A, R-404A, R-134a, R-407A/C/F, R-448A, R-449A, R-507A. All A1 — lower toxicity, no flame propagation.
A1 refrigerants have no flammability charge limit under ASHRAE 15. Equipment design and install conditions follow standard mechanical code without flammability-specific provisions.
A1 refrigerants are largely on the AIM Act phase-down curve due to GWP, not safety. R-410A is gone from new equipment because of GWP, not because it’s flammable (it isn’t).
R-32, R-454A, R-454B, R-454C, R-455A, R-1234yf, R-1234ze, R-513A. All A2L — lower toxicity, lower flammability than A2/A3.
A2L refrigerants have lower flame propagation velocity and higher minimum ignition energy than A2 or A3 hydrocarbons. Burning velocity is small enough that ASHRAE 15 treats them as a distinct class with their own charge limits.
Charge limits for A2L equipment depend on the equipment category, refrigerant LFL, and room volume. ASHRAE 15-2022 introduced specific Refrigerant Concentration Limits (RCL) and charge calculation methods for A2L — different from A2 and A3.
Florida Mechanical Code 2023 amendments incorporated A2L install requirements consistent with ASHRAE 15. Tampa Bay AHJ interpretation has been consistent with FMC.
R-290 (propane), R-600a (isobutane), R-1270 (propylene). All A3 — lower toxicity, higher flammability.
A3 refrigerants have hydrocarbon-class burning velocity and ignition energy. Charge limits are tight — typically 150g per circuit for self-contained commercial refrigeration, with revised UL/IEC standards allowing up to 500g for some categories.
Equipment using A3 refrigerants must be UL-listed (UL 60335-2-89 for commercial refrigerating appliances, UL 60335-2-40 for HVAC). Field-built or field-charged A3 systems are not legal under typical Florida AHJ interpretation.
R-123, R-1233zd, R-514A. B1 (low-pressure chiller refrigerants) or B2L (newer low-pressure replacements). Higher toxicity — OEL below 400 ppm.
Used in centrifugal chillers and some industrial process applications. Equipment ventilation, leak detection, and personnel exposure controls are different from A-class systems.
Out of scope for most of our work — we don’t service low-pressure centrifugal chillers as a primary line.
A1: no flammability charge limit. RCL applies for room concentration in case of leak.
A2L: charge limit by application, by room volume, by equipment category. ASHRAE 15-2022 calculation method is the working reference. Most commercial walk-ins and rooftop units sit comfortably under the limits with normal-volume mechanical rooms.
A3: 150g per self-contained refrigeration circuit (some categories now up to 500g under updated UL/IEC). Built-up systems with A3 refrigerants are tightly constrained and not typical in commercial buildings.
B-class: refrigerant-specific RCL and machine-room ventilation requirements per ASHRAE 15.
Florida Mechanical Code 2023 (FMC 2023) is the working install code. ASHRAE 15-2019 / 15-2022 is incorporated by reference for A2L and other class-specific requirements.
Equipment listings (UL 60335-2-40, UL 60335-2-89) are the second authoritative reference. The listing limits where and how the equipment can be installed.
Tampa Bay AHJs (Hillsborough County, City of Tampa, Pinellas County, City of St. Petersburg, Pasco County, etc.) have been interpreting FMC 2023 consistently. Confirm current AHJ position for any non-standard installation.
For technicians: tools rated for the refrigerant class. A2L tools (gauges, hoses, recovery, leak detection) for A2L work. A3 tools (hydrocarbon-rated leak detection, ignition controls) for A3 work. Many modern multi-class tools cover both.
For operators: install conditions, ventilation, and equipment locations agreed at design and install time. Field changes — moving equipment, modifying ventilation, adding equipment to a mechanical room — require re-evaluation against the equipment’s charge and the room’s RCL.
For specifiers and engineers: Refrigerant class is a design input alongside capacity, GWP, and capex. The class affects the mechanical room, the gas piping, the relief venting, and the service procedures over the equipment’s life.
For typical commercial mechanical rooms with normal volumes and standard ventilation, R-454B equipment installs cleanly under FMC 2023 / ASHRAE 15. Confined spaces and basement use require specific evaluation.
A2L is a subset of A2 with lower burning velocity and higher minimum ignition energy. ASHRAE 15 treats A2L as a distinct class with its own charge calculation methods. R-32, R-454-family, R-1234yf, R-1234ze are all A2L.
Yes — self-contained R-290 equipment under the 150g charge limit (or higher under updated UL standards) is listed for installation in standard commercial kitchens. The equipment listing addresses worst-case-leak scenarios.
They have low burning velocity and high minimum ignition energy. They will burn under specific conditions; they are unlikely to ignite from typical kitchen ignition sources. ASHRAE 15 charge limits and equipment listings address the realistic risk.
For most installations, no — typical rooms with normal ventilation and the calculated charge limit accommodate A2L equipment. Specific installations (large central plants, basement use, high-density mechanical rooms) require engineering evaluation.
Suncoast Cold Systems services commercial refrigeration and HVAC across Tampa, St. Petersburg, Clearwater, Brandon, Riverview, Temple Terrace, and Wesley Chapel. 24/7 dispatch. Specific response targets are agreed in writing for service-contract customers, by site tier and severity. State Certified Class A Air Conditioning Contractor (FL #CAC1824642), EPA 608 Universal, OSHA 30 Construction.
The A2L blend family.
A3 hydrocarbon refrigerant in self-contained equipment.
The two A2L paths in commercial HVAC.