R-454B charge limit and minimum room area
R-454B became mandatory for new US residential systems on 1 January 2026 — and it is a mildly flammable A2L fluid, so the first engineering question is not "how big is the compressor" but "is this charge even allowed in this room?". Size the safety cap before you size anything else.
Why this tool exists
R-454B is the mainstream R-410A replacement for new residential and light-commercial equipment.
It is classified A2L (lower flammability) — so charge quantity is capped by room volume and ventilation, not by the equipment alone.
Standards govern the cap: ISO 5149 / EN 378 and ASHRAE 15/34 minimum-room-area rules. Getting this wrong is a code failure, not a comfort complaint.
Legacy teaching tools (CoolPack-era) and OEM selectors do not cover the A2L-era fluids, which is exactly the gap this free tool fills.
Fluid facts (from the app's refrigerant database)
Single-sourced from the same dataset the calculators use — not retyped for this page.
GWP values are the database's cited values (IPCC AR5). Safety classes follow ASHRAE 34.
Charge-limit calculator
Enter the room and the refrigerant. The tool applies the fluid's LFL and the EN 378 / ISO 5149 room model to return the maximum allowable charge and the minimum room area — the number that decides whether an A2L system can go in this space at all.
A2L/A3 Charge Limit — ISO 5149 / EN 378
Maximum refrigerant charge allowed in a machine/occupied room for flammable fluids. Decides fluid + layout before you size anything. Deterministic table (LFL per fluid) + EN 378 simplified models.
How to read the result
Floor area and height set the room volume. A2L limits scale with volume: the same system that passes in a plant room fails in a small bedroom.
People factor reflects occupancy, which tightens the permitted concentration in occupied spaces.
Air changes per hour (ACH) accounts for ventilation or a leak-detection-and-ventilation system; more air changes buys more permitted charge.
If your design charge exceeds the cap, the fix is one of: add ventilation/leak detection, split the circuit, or change fluid. The tool tells you which lever is available before you commit to a layout.