A2L Refrigerant Charge Limit Calculator

3.91 lb (1.776 kg). Two documents publish an m1 for R-454B and this calculator works to the LOWER of them. UL 60335-2-40 4th edition sets its threshold at 6 times the LFL, and R-454B's LFL is 0.296 kg/m3 in UL Table BB.1DV, so 6 x 0.296 = 1.776 kg, which is 3.91 lb rounded down. ASHRAE 15.2-2024 Table 9-1 publishes 4.0 lb. For R-454B the UL figure is the lower one, so 3.91 lb is the answer. At or below it, ANSI/ASHRAE 15.2-2024 Figure 9-1 routes the system straight to 'system charge in compliance' with no room-area step at all. ⚠ The two figures are close because both derive from the same LFL, and they are not interchangeable: Table 9-1's own title calls its values charge levels for MITIGATION, and above that figure ASHRAE 15.2-2024 section 5.3 requires an integral refrigerant detection system unless an exemption applies. Which figure is lower flips per refrigerant: for R-32, R-454A and R-1234yf the ASHRAE value is the lower one and it is what this calculator uses.

4 lb (1.81 kg), and R-32 is the case where the two published figures disagree in the direction that matters. UL 60335-2-40 4th edition's 6 x LFL gives 6 x 0.306 = 1.836 kg, which is 4.04 lb rounded down, but ANSI/ASHRAE 15.2-2024 Table 9-1 publishes 4 lb, and 15.2 is the residential standard this calculator follows. The lower figure governs, so this calculator uses 4 lb and applies the room-area math above it: between 4 and 4.04 lb the UL figure would clear the install and ASHRAE sends it to the area math, and the area math is what this tool follows. Separately, equipment certified to the 3rd edition or IEC edition 6 (which includes most published R-32 mini split installation tables, like Daikin's) uses the older m1 = 4 x LFL = 1.224 kg (2.70 lb). Check which edition your equipment is listed to; the installation manual's table is the binding one.

The gravity dispersal equation from UL/IEC 60335-2-40 Annex GG: m_max = 2.5 x LFL^(5/4) x h0 x sqrt(A), where LFL is the lower flammability limit in kg/m3, h0 is the release height in meters, and A is the room area in square meters. The 4th edition and ASHRAE 15.2-2022 (Addendum a) add two more constraints: a concentration cap of 0.5 x LFL x h x A and an absolute ceiling of 52 x LFL. With continuous air circulation, or circulation started by a refrigerant detection system, the gravity term (and only that term) is doubled with an airflow factor AF = 2; the cap and the ceiling are not.

0.6 m for floor-mounted units, 1.8 m for wall-mounted units, and 2.2 m for ceiling or cassette units, per the UL 60335-2-40 Annex GG convention. The 1.0 m window-unit height is an EN 378 / FETA TB04 convention, not an Annex GG value. For US ducted systems the height is the supply-air discharge point into the room, clamped to 2.0 to 9.0 ft (0.6 to 2.74 m) per ANSI/ASHRAE 15.2-2024 Table 9-3 footnote a. Height above the room inside ductwork does not count. That discharge-point basis is UL 60335-2-40 Annex GG's, which is what this calculator computes with. ANSI/ASHRAE 15.2-2024 section 9.4.3.3 sets a ducted dispersal height on a different basis, the mean of the actual ceiling heights of the spaces served with no height above 9.0 ft counted, and this calculator does not compute it. For ordinary ceilings the Annex GG figure is the lower and therefore the stricter of the two; where a mean capped ceiling height falls below about 7.2 ft it is the higher, by up to about 3 percent on the charge.

Test basis. ASHRAE 34-2019 lists 0.3526 kg/m3 using the worst-case fractionated formulation at 23 C, while UL 60335-2-40 Table BB.1DV uses the worst-case formulation at 25 C, which gives 0.296 kg/m3. Manufacturer installation math (York/JCI, Trane) uses the UL value, and it is the more conservative choice for charge limits, so this calculator computes with 0.296.

No. R-290 is class A3 (higher flammability), not A2L. The Annex GG room-area formula on this page applies to A2L refrigerants only. A3 charge limits come from different clauses with far smaller allowances (on the order of hundreds of grams for comfort cooling), and US model codes had not adopted A3 comfort-cooling splits as of 2026. Follow the equipment listing exactly.

Above m1, the charge level ANSI/ASHRAE 15.2-2024 Table 9-1 publishes for that specific refrigerant. m1 is not one number: it is 4.0 lb for R-32, R-454B and R-454C, 4.2 lb for R-452B, 3.8 lb for R-1234yf, 3.7 lb for R-454A and 2.9 lb for R-457A. A single 4.0 lb figure is widely quoted from ASHRAE Standard 15 section 7.6.2.3, but Standard 15 and Standard 15.2 are different documents, and 15.2 is the residential one this calculator follows. Section 5.3 of 15.2 is written as a set of exemptions rather than a trigger. Above m1 an integral detection system is required unless the system meets one of three, and every one of them requires the system charge to stay below the maximum charge first: (a) a ducted system with the equipment and all duct openings at least 5.9 ft (1.8 m) above the finished floor, where the maximum is computed on the smallest-room area of 9.4.2.2 and not on the aggregate; (b) a ducted system with the indoor equipment at least 3.9 ft (1.2 m) above the finished floor; or (c) any other system, ducted or not, under the maximum charge. Exemption (a) naming 9.4.2.2 specifically is the trap: you cannot claim the aggregate area under 9.4.2.1 and the mounting-height exemption at the same time. That is why most 2025+ R-454B ducted systems ship with a leak detection sensor from the factory. What the detection system buys you is the dispersal area itself: with one fitted, or with continuous circulation, section 9.4.2.1 lets you use the aggregate floor area of every space on the same supply ductwork; without one, section 9.4.2.2 makes you use the smallest single room on that ductwork. Keep the two ducted heights apart: the 5.9 ft duct-opening figure above is a test on where your openings sit, while under the UL ducted-system rules the dispersal height becomes a constant 7.2 ft (2.2 m), a different quantity that this calculator leaves to the manufacturer's installation tables. They print a few lines apart in the same source and swapping them is how the wrong number reached this page once before.

Two ceilings apply. The standard's own ceiling is m2 = 52 x LFL (33.9 lb for R-454B, 35.1 lb for R-32) for the room-area path; above that, mitigation requirements take over. Separately, IRC 2024 section M1411.6 caps the A2L charge of an individual refrigeration system at 34.5 lb, and M1411.2 requires that equipment be listed and labeled to UL/CSA 60335-2-40. The IRC governs detached one- and two-family dwellings and townhouses not more than three stories (R101.2), so an apartment building or a commercial job falls under whichever mechanical code your jurisdiction applies instead. State adoption of the 2024 I-codes is uneven in 2026, so confirm the edition your jurisdiction has adopted. Multiple systems can serve a large house, each under the cap.

No. This calculator implements the standards math and reproduces ANSI/ASHRAE 15.2-2024's published Table 9-3 (76 cells) and Table 9-4 (80 cells) as a check, but the equipment listing and installation manual are the binding documents, and they reflect the exact edition, ventilation, and mitigation features of your unit. Use this tool to understand and sanity-check the limits, then follow the manual and your AHJ.

Yes, and this calculator computes it. ASHRAE 15.2-2024 Equation 9-2 is m_max = C x (M + MV): M is the dispersal-volume term the room-area math gives you, and MV is an additional charge earned by mechanical ventilation, read from published Table 9-4. Enter the airflow serving the dispersal space and the limit rises. Three limits are worth knowing before you count on it. Table 9-4 publishes no row below 20 cfm, so below that no credit is given rather than a small one. It stops crediting at 400 cfm, so a bigger fan earns nothing beyond that point. And the ventilation must run continuously or start automatically on the leak detection system to be claimed at all. Between published rows the standard's own footnote permits interpolation, which is what this calculator does; it never evaluates the informative appendix formula, which reads higher than the published table on a majority of the low-airflow cells where residential ventilation actually sits.

It depends on one thing, and getting it backwards is the most common way this calculation goes wrong. ANSI/ASHRAE 15.2-2024 section 9.4.2 splits on whether the system has a refrigerant leak detection system or continuous air circulation. With one, section 9.4.2.1 lets you use the aggregate floor area of every space connected to the same supply ductwork, though you must leave out any space whose airflow a zone damper can cut off. Without one, section 9.4.2.2 makes you use the smallest single room served by that ductwork, which is usually a far smaller number and a far stricter limit. The difference between the two is frequently the whole question of whether an install complies. Select the system type in the calculator and it relabels the area field to tell you which figure to enter, and names the clause its answer rests on.

Enter the charge actually in the system and the calculator returns a pass or fail plus the four routes back under the limit it can derive by inverting the same terms the limit came from, rather than offered as advice. A larger dispersal area, with the specific square footage that would admit the charge. A greater release height, with the height required, though the standard stops crediting height at its own clamp. On a ducted system without detection, fitting a refrigerant detection system or running continuous circulation, which moves you from section 9.4.2.2 to 9.4.2.1 and can change the area you are entitled to use by an order of magnitude without moving any equipment. And mechanical ventilation, with the smallest published airflow that covers the shortfall. Two further routes exist in the standard and this calculator does not compute either, so the list above is not the whole of ANSI/ASHRAE 15.2-2024: section 9.6 allows safety shut-off valves that reduce the releasable charge, which is then compared against the limit instead of the full system charge, and it applies only where the manufacturer's installation instructions specify those valves; and section 9.4.2.3 allows spaces joined by an open passageway to be aggregated into one dispersal floor area, which changes the area and therefore the limit. Where the charge is beyond everything the published tables can reach, the tool says so rather than naming a route nobody can take.

Enter the charge and the room and the calculator names the smallest airflow that covers the gap, interpolated from ANSI/ASHRAE 15.2-2024 Table 9-4 as its own footnote permits. The rate it names is a requirement rather than a suggestion, and it is sized against what the room actually supplies rather than against the ceiling, so re-entering it clears the limit. Two boundaries bind the answer: nothing is credited below 20 cfm because the table publishes no row there, and nothing further is credited above 400 cfm because that is where the published table stops. Entering a rate replaces whatever rate is already in the calculation rather than stacking on top of it, so the figure shown is the total the space needs. The manufacturer's installation instructions still govern the installed system.