Knowledge/Calculators and tables/Minimum room area for mildly flammable A2L refrigerants
Minimum room area for mildly flammable A2L refrigerants
For flammable refrigerants like R32, your legal obligation is to follow the minimum floor area the manufacturer states, not to run a formula. AS/NZS 60335.2.40 makes the manufacturer do the calculation and show the result in the installation instructions. The method on this page is for understanding what the manual tells you, not for compliance.
- What you must follow
- The manualmanufacturer's stated minimum area
- Formula
- 2.5 × LFL^1.25 × h0 × A^0.5max charge in kg. LFL is the lower flammability limit
- h0, wall mounted
- 1.80.6 floor, 1.0 window, 2.2 ceiling
- Old 20% rule
- Deadnot applicable to flammable refrigerants
Read
this
first
The manufacturer runs the calculation, not you
In short, the manufacturer does the maths, the manual tells you the smallest room the unit can go in, and you stay within it. Here's clause 2.3.3 of the Australian Refrigeration Council (ARC) Code of Practice Part 2, word for word.
"Considering the number of variables and the complexity of the required calculations for air conditioners that use flammable refrigerants, AS/NZS 60335.2.40 mandates that the manufacturer performs the calculations and that the installation instructions clearly show the resulting minimum floor area into which the air conditioner can be installed. Air conditioning installations must conform to those application limits."
So the compliant process is simple. Open the manual, find the stated minimum floor area, and install within it. Don't run a formula off a website, including this one.
The old habit from non-flammable A1 refrigerants is explicitly dead, too. "The common rule of thumb calculation of 20 per cent room volume, previously used for A1 refrigerants, is not applicable for systems using a flammable refrigerant."
How does the minimum room area formula work?
The formula comes from ISO 5149-1 and IEC 60335-2-40 Annex GG.
- Maximum charge in kg, m_max = 2.5 × LFL^(5/4) × h0 × A^(1/2)
- Rearranged for minimum area, A_min = ( m / (2.5 × LFL^1.25 × h0) )^2
- m is the charge in kg. LFL is the lower flammability limit in kg/m³, the lowest concentration of refrigerant in air that can catch fire. A is the room floor area in m².
h0 is the installation height factor, and it's the biggest lever in the whole calculation. It's 0.6 floor mounted, 1.0 window mounted, 1.8 wall mounted and 2.2 ceiling mounted.
Under a certain charge, room size doesn't matter at all. For A2L refrigerants (mildly flammable, like R32) that cut-off is 6 times LFL, which is 1.836 kg for R32 and 1.782 kg for R454B, taking R454B as A2L, which is how it's commonly classed - we couldn't confirm that from an Australian primary source, so check the manufacturer's safety data sheet. For A2 and A3 (flammable and highly flammable, like R290 propane) it's 4 times LFL, which is 0.152 kg for R290. That last figure is where the well-known 150 gram limit comes from.
Why does mounting height matter so much?
| Mounting | h0 | R32 max charge at 10 m² |
|---|---|---|
| Ceiling | 2.2 | 3.96 kg |
| Wall | 1.8 | 3.24 kg |
| Window | 1.0 | 1.80 kg |
| Floor console | 0.6 | 1.08 kg |
A floor console gets only about 27 per cent of the allowable charge of a ceiling cassette in the same room. That's the least intuitive thing on this page, and it's worth knowing when a customer asks for a floor unit in a small room.
The logic is simple once you see it. A leaking refrigerant that's heavier than air sinks toward the floor, so the higher the unit, the more air the leak mixes into on the way down before it can build up to a flammable level.
How does a typical bedroom work out, and can you trust the maths?
Take a typical Australian bedroom, 3.0 m by 3.5 m, so 10.5 m², with a wall mounted unit.
| Refrigerant | No-restriction threshold | Max charge at 10.5 m² | Verdict |
|---|---|---|---|
| R32 | 1.836 kg | 3.32 kg | A typical 2.5 to 7 kW hi-wall holds 0.5 to 1.8 kg, so it sits under the threshold and no area calculation is needed. 1.8 kg is close to the line, so check the actual charge on the nameplate |
| R454B | 1.782 kg | 3.20 kg | Same conclusion for most units, if it's A2L as commonly classed. The top of that range, 1.8 kg, is just over 1.782 kg, so check the nameplate |
| R290 | 0.152 kg | 0.245 kg | Only a very small or specially engineered unit fits |
Here's the check, so you can judge whether to trust the arithmetic. A published article says the then-current standard allowed 334 g of an A3 refrigerant in a 20 m² room. Running this formula with LFL 0.0377 and h0 1.8 gives exactly 334 g. That confirms both the formula and the LFL value the standard uses.
What's the trap on ducted systems?
Straight from the ARC code. "For installation of split system ducted air conditioners, the maximum refrigerant charge limits are particularly important. The smallest room the system serves dictates the maximum refrigerant charge in the system that can be safely installed."
Read that twice if you install ducted R32. Not the house area. Not the average room. The smallest room on the system. A powder room or a small study on the same ductwork sets the limit for the whole charge.
There's a second warning attached. Ducted indoor units carry an extra hazard where the indoor unit sits in a confined space, because a leak could pool or get trapped and go over the refrigerant concentration limit.
And one figure we won't publish
We're not publishing a numeric A2L or A3 charge limit as Australian law. Australia adopted the relevant standard with changes (a modified adoption), and the Australian version is behind a paywall. The 988 g and 7.5 kg figures you'll hear quoted describe an international draft. They're not Australian law. That's exactly why everything numeric above is marked computed.
Want a second opinion on a number?
Calculators are only as good as the assumptions under them, and the assumptions are where jobs go wrong.
If a figure looks off against what you see on site, that instinct is usually worth more than the calculator. Ask Kevin.
Who this is for: small and medium HVAC contractors in Victoria. If you're a homeowner after a rebate or a repair, you need a licensed contractor, not us, and yours can point you the right way.
Review date: 1 April 2027. Figures in this area change without much notice and this page carries some that will go stale. Every number above is dated and sourced so you can check it yourself. If you find something out of date here, tell us and we will fix it.