R290 Refrigerant Explained: Propane and the Charge Limit

R290 is propane carrying a refrigerant designation. It is a hydrocarbon already at work in heat pumps and commercial refrigeration, described on producer technical sheets. The molecule was never engineered for the role: it was available, moves heat well, and warms the atmosphere by almost nothing.

That warming figure is why the name keeps surfacing. A Green Cooling Initiative paper on safety standards places hydrocarbons at 1 or below. The limit written for household aircon here sits at 750, and propane sits hundreds of times below that ceiling.

The pressure reshaping refrigerant supply barely touches it. The HFC phase-down shrinks fluorinated gas entering the country each year, and propane is not fluorinated. Whatever the schedule does to the current generation, it does not reach this one.

If the warming problem is answered outright, something else holds propane back: a letter and a digit.

Propane is graded A3. ASHRAE Standard 34 defines three flammability classes, and ASHRAE's own fact sheet describes class 3 as covering highly flammable refrigerants such as hydrocarbons. The letter grades toxicity, where A means lower toxicity. The digit parts propane from every household split here.

R32 sits at A2L, and what that classification means inside a flat has its own page. Propane belongs to a different class. Reading across the grades gives the wrong picture in both directions.

Two published figures describe class 3 in practice. A producer sheet gives propane a lower flammability limit of 2.1 percent by volume, or 0.038 kilograms per cubic metre of air. Below that concentration nothing ignites. The autoignition temperature is 470 degrees Celsius.

A third property on that sheet is easy to miss. Propane sold for domestic burning is odourised deliberately, so a leak announces itself. The refrigeration grade is not, and the producer states the consequence: no added smell means a release is not easily detected.

None of this makes propane exotic or new. It has run sealed inside domestic fridges for years. What changes as equipment grows is how much of the gas there is, and which side of a wall it sits on.

A flammability limit stated as a concentration becomes a weight once the room is named. That producer figure is a density, meaning mass per unit of air. Multiply it by a bedroom's volume and the answer carries that room to the threshold; take off a margin and a charge limit appears.

IEC 60335-2-40 does that sum for air conditioners and heat pumps. The International Institute of Refrigeration reads its 2022 edition this way: escaped charge must not take the room past half the flammability limit.

The standards constrain quantity two ways at once. An upper charge limit is a flat cap tied to the application and where the system sits. An allowable charge limit is a function of room size, and a design must satisfy both.

For propane under that standard the shape is precise. Below 0.15 kilograms there is no room-size dependency. Above it the allowable charge climbs with floor area, stopping at an upper limit of around 1 kilogram. Beyond that a larger room permits nothing further.

Where the circuit sits moves the ceiling most. The same summary allows roughly 1 kilogram indoors against about 5 kilograms outside or inside an enclosure. Occupied space is what gets protected, so taking the refrigerant out of it multiplies the permitted quantity.

The same paper plots capacity against charge for a propane air conditioner, with curves separated by seasonal efficiency. A higher efficiency rating needs more refrigerant for the same capacity, as does a larger capacity at any efficiency. The cap is quietly a cap on the machine, on both axes.

Nothing about propane cools badly; what limits it is a number written to keep a room below a threshold.

Design follows the ceiling. Once the permitted quantity is tied to the room, a machine must need less refrigerant or hold it where the cap is looser. Both routes exist on the market.

Keeping the circuit outdoors is cleaner. A sealed unit standing outside, sending water or air into the building, puts the whole charge beyond occupied space. Self-contained and monobloc designs exist for that reason, and chilled water systems apply the same separation at building scale.

Where the circuit comes indoors, the standard trades allowance for engineering. The Green Cooling Initiative paper lists four measures: tighter construction, housing shaped to disperse a leak, guaranteed airflow so refrigerant cannot settle at floor level, and valves that limit how much charge reaches the room.

Materials change too, which is why a machine built for one gas will not take another. A propane producer sheet rules out EPDM rubber, natural rubber and silicone, and warns that polyolester oil dissolves too readily in hydrocarbons. Mineral and alkylbenzene lubricants suit it better.

Those measures are why the ceiling moved. Older formulas assumed the entire charge emptied into the room instantly, forcing the mass down. Guarantee a slow or well-mixed release, and more refrigerant is tolerated before the mixture reaches the threshold. Recent standards work prices that in.

The effect is uneven across machine types, which is where a Singapore household comes in. The paper sets out how much cooling propane delivers in each system, straight out of the charge limits above.

Propane is not waiting for permission. It has run in domestic fridges for years under the 150 gram cap in IEC 60335-2-24, and in plug-in cabinets under roughly 500 grams. Producers list heat pumps and commercial refrigeration as its ordinary territory.

Split air conditioners are harder, and one market got there first. The International Institute of Refrigeration credits India, where a manufacturer put propane splits into the local market from 2012 with trained installers. China, Southeast Asia and South America have converted production lines since, but beyond small and portable units, market introduction has stayed limited.

The installer network earns its place. Charge limits govern what may be built, but a service visit decides whether the design survives the field. A class 3 refrigerant asks more of whoever opens a circuit, so shipping equipment without training does half the job.

Producers warn hydrocarbon refrigerant must arrive very pure, because sulphur or water in the cylinder degrades the oil and reaches the compressor. Impure product is often cut with other hydrocarbons, shifting behaviour in the circuit. Counterfeit refrigerant is not built to respect that tolerance.

Locally, the visible movement is commercial. NEA announced in May 2026 that refrigerants above a warming figure of 150 will be barred from commercial refrigeration from July 2027, and from car air conditioning from July 2028. Neither measure names a refrigerant; a ceiling that low sits under today's household split gas, so those categories must move elsewhere.

For household splits here, no published instrument mentions propane at all. It clears the domestic ceiling by a wide margin, which is a permission rather than a plan. Which formats manufacturers engineer, what the standards allow in HDB room sizes, and whether the trade is equipped for servicing are three separate questions.

• •Start from what your own machine holds. The rating plate will not read propane on a household split sold here.
• •Read a charge limit as a condition on the room, not a rating on the product. Identical equipment can be permitted in one space and refused in another.
• •Weigh the format ahead of the gas. Bedrooms hanging off one condenser spread a single charge across long pipe runs, where a ceiling binds first.
• •Discount any date given for propane reaching household splits here. No published instrument sets one, and no schedule implies one.
• •Judge a technician on whether they know the class of the gas in front of them. That question separates more people than any certificate.