HVAC Compliance Calculator
A2L Refrigerant Charge Limit Calculator
R-454B and R-32 systems have a maximum charge for every room size, set by UL 60335-2-40 and ASHRAE 15.2. Enter the room and the mounting height to get the maximum charge, or enter the charge to get the minimum room area, with the math shown.
This tool implements the standards math for understanding and sanity-checking limits. The equipment listing, the manufacturer's installation manual, and your AHJ govern every real installation.
Release Heights by Installation Type
| Installation | h0 | Source |
|---|---|---|
| Floor-mounted (console, floor coil) | 0.6 m (2.0 ft) | FETA TB04, Daikin tables |
| Window-mounted | 1.0 m (3.3 ft) | IEC/EN 378 convention (FETA TB04) |
| Wall-mounted (high-wall mini split) | 1.8 m (5.9 ft) | FETA TB04, Daikin tables |
| Ceiling / cassette / supply register | 2.2 m (7.2 ft) | FETA TB04, Daikin tables, ASHRAE 15.2 Table 9-3 basis |
Lower release height means less air column for a leak to disperse into, so floor-mounted units have far stricter limits than ceiling cassettes at the same room size.
LFL Values and Key Thresholds by Refrigerant
| Refrigerant | Class | LFL used here | ASHRAE 34 LFL | m1 (no restriction) | m2 ceiling |
|---|---|---|---|---|---|
| R-32 | A2L | 0.306 | 0.306 | 4.05 lb | 35.1 lb |
| R-454B | A2L | 0.296 | 0.3526 (WCFF) | 3.91 lb | 33.9 lb |
| R-452B | A2L | 0.3105 | 0.3105 | 4.11 lb | 35.6 lb |
| R-454A | A2L | 0.294 | 0.2939 (WCFF) | 3.89 lb | 33.7 lb |
| R-454C | A2L | 0.290 | 0.2895 (WCFF) | 3.84 lb | 33.2 lb |
| R-455A | A2L | 0.432 | 0.4321 | 5.71 lb | 49.5 lb |
| R-1234yf | A2L | 0.289 | 0.289 | 3.82 lb | 33.1 lb |
| R-1234ze(E) | A2L | 0.303 | 0.303 | 4.01 lb | 34.7 lb |
| R-290 (propane) | A3 | 0.038 | 0.038 | n/a | n/a |
Sources: ASHRAE 34-2019 Addendum f Tables 4-1/4-2; UL 60335-2-40 Table BB.1DV per the York/JCI R-454B whitepaper; EN 378 values per the FETA A2L guide. m1 and m2 shown for the UL 4th edition / ASHRAE 15.2 regime (6 x LFL and 52 x LFL).
Which Edition Applies to Your Equipment
The charge limit math changed between standard editions, and both regimes are live in the field in 2026. UL 60335-2-40 3rd edition (published 2019, harmonized to IEC edition 6) was EPA's SNAP certification baseline for A2L residential equipment and uses the gravity equation alone. The 4th edition (published December 2022, harmonized to IEC edition 7) added the concentration cap, raised the tier thresholds (m1 from 4 x LFL to 6 x LFL, m2 and m3 doubled), and introduced the airflow factor; ASHRAE 15.2-2022 Addendum a aligned the residential standard to it, and 2025+ US equipment documentation (York, Trane, Carrier) is written against it.
| Tier | IEC ed 6 / UL 3rd ed / EN 378 | IEC ed 7 / UL 4th ed / ASHRAE 15.2 |
|---|---|---|
| m1: no room-size restriction at or below | 4 x LFL (R-32: 1.224 kg / 2.70 lb) | 6 x LFL (R-454B: 1.776 kg / 3.91 lb) |
| m2: room-area formula applies up to | 26 x LFL | 52 x LFL (R-454B: 33.9 lb) |
| m3: mitigation territory ends, machinery room rules | 130 x LFL | 260 x LFL |
Between m1 and m2, the minimum-room-area math on this page governs unventilated installations. Above m2, circulation airflow, ventilation, or other mitigation per Annex GG (GG.3, GG.8, GG.10) is required, and above m3 the system belongs in machinery room territory. This calculator shows both regimes so the number you compute matches the edition your equipment is certified to.
Worked Examples, Verified Against Published Tables
Example 1: R-32 wall-mounted mini split, 1.8 kg (IEC ed 6 regime)
A 4 lb (1.8 kg) R-32 charge on a high-wall unit (h0 = 1.8 m). Minimum area = (1.8 ÷ (2.5 × 0.3061.25 × 1.8))² = (1.8 ÷ 1.024)² = 3.09 m² = 33.3 ft². Daikin's published R-32 installation table lists exactly 3.09 m² for this row, which is one of the checks this engine is validated against. Almost any real bedroom passes; the limit starts to bite on floor-mounted units, where the same charge needs 27.8 m² (299 ft²).
Example 2: R-454B ducted system, 6 lb (ASHRAE 15.2 regime)
A 6 lb (2.72 kg) R-454B system with a supply register at 9 ft (2.74 m), no circulation credit. Gravity area = (2.72 ÷ (2.5 × 0.2961.25 × 2.74))² = 3.31 m², concentration-cap area = 2.72 ÷ (0.5 × 0.296 × 2.74) = 6.71 m². The larger one governs: 6.71 m² = 72 ft². The York/JCI R-454B whitepaper publishes the same 6.7 m² figure for this case. Since 6 lb exceeds the 4 lb releasable-charge line, this system also ships with a factory refrigerant detection system per ASHRAE 15 section 7.6.2.3.
Example 3: How much R-32 fits a 200 ft² room (ASHRAE 15.2 Table 9-3)
Ceiling supply at 7.2 ft (2.2 m), 200 ft² (18.58 m²). Without circulation: gravity term = 2.5 × 0.3061.25 × 2.2 × √18.58 = 5.40 kg, cap = 0.5 × 0.306 × 2.2 × 18.58 = 6.25 kg, so 5.4 kg (11.9 lb) governs. With continuous circulation the gravity term doubles to 10.79 kg and the 6.25 kg cap governs instead: 6.3 kg (13.8 lb). Both numbers match ASHRAE 15.2-2022's published Table 9-3 row for 200 ft².
Frequently Asked Questions
What is the maximum R-454B charge with no room-size restriction?
3.91 lb (1.776 kg). UL 60335-2-40 4th edition sets the no-restriction threshold m1 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. Manufacturer literature rounds this to 4 lb. Trane's residential documentation uses the same 3.91 lb line for when factory leak detection becomes required. Below that charge, the room-area formula does not restrict the installation.
What is the maximum R-32 charge with no room-size restriction?
Under the UL 60335-2-40 4th edition and ASHRAE 15.2 regime, m1 = 6 x 0.306 = 1.84 kg (4.05 lb). 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.
What formula sets A2L refrigerant charge limits?
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.
What release height h0 do I use?
0.6 m for floor-mounted units, 1.0 m for window units, 1.8 m for wall-mounted units, and 2.2 m for ceiling or cassette units, per the IEC/UL 60335-2-40 Annex GG convention. For US ducted systems the height is the supply-air discharge point into the room, clamped between 2.0 and 9.0 ft (0.6 to 2.74 m) per ASHRAE 15.2. Height above the room inside ductwork does not count.
Why do R-454B LFL values differ between sources?
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.
Does this calculator apply to R-290 (propane) systems?
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.
When is a refrigerant detection system (RDS) required?
Per ASHRAE 15 section 7.6.2.3, ducted systems with a releasable charge over 4.0 lb (1.8 kg) and duct openings below 7.2 ft need a factory-installed refrigerant detection system. That is why most 2025+ R-454B ducted systems ship with a leak detection sensor from the factory. When the RDS initiates circulation airflow, the charge limit math also improves: the airflow factor AF doubles the gravity term, and under the UL ducted-system rules the dispersal height becomes a constant 7.2 ft (a detail this calculator leaves to the manufacturer's installation tables).
Is there a maximum A2L charge for houses regardless of room size?
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 caps the A2L charge of an individual system at 34.5 lb in dwellings and requires equipment listed to UL/CSA 60335-2-40. Multiple systems can serve a large house, each under the cap.
Can I use this instead of the manufacturer's installation tables?
No. This calculator implements the standards math and reproduces published manufacturer tables (Daikin R-32, York R-454B, ASHRAE 15.2 Table 9-3) 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.
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Room checks out? Charge it right.
Once the charge limit clears, verify the actual charge with superheat and subcooling. The calculator handles PT interpolation for R-454B and R-32 with bubble and dew point glide, TXV targets, and a four-quadrant diagnostic.