R290 refrigerant explained: propane and the charge limit

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

That last property is why the name keeps surfacing. A Green Cooling Initiative paper on safety standards places hydrocarbons at 1 or below on the warming scale. The gwp limit written for household aircon here sits at 750. Propane does not squeeze under that ceiling. It sits hundreds of times below it.

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

One question survives all of that. If the warming problem is answered outright, and the chemistry is cheap and understood, something else must be holding it back. That something is 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 the hydrocarbons. The letter grades toxicity, and an A means lower toxicity. The digit is where propane parts company with everything in a household split here.

R32 sits at A2L, and what the a2l classification means inside a flat has its own page. Propane belongs to a different class, and the whole of this article concerns that one. Reading across from one grade to the other gives the wrong picture in both directions.

Two published figures describe class 3 in practical terms. A producer technical sheet gives propane a lower flammability limit of 2.1 percent by volume, which works out to 0.038 kilograms per cubic metre of air. Below that concentration nothing ignites. The autoignition temperature on the same sheet is 470 degrees Celsius.

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

None of this makes propane exotic or new. It has been running in kitchens for years, sealed inside the fridge. What changes as equipment grows is not the gas at all. It is how much of it there is, and which side of a wall it sits on.

A flammability limit stated as a concentration becomes a weight the moment you name the room. That producer figure is a density, meaning mass of propane per unit of air. Multiply it by the volume of a bedroom and the answer is the quantity that would carry that bedroom to the threshold. Take a margin off the answer and the shape of a charge limit appears.

IEC 60335-2-40 is the standard doing that sum for air conditioners and heat pumps. The International Institute of Refrigeration reads its 2022 edition this way. Whatever charge can escape must not take the room past half the flammability limit. The rest of the rules describe how that one condition gets met.

Safety standards constrain the quantity two ways at once, and the Green Cooling Initiative paper separates them cleanly. An upper charge limit is a flat cap, tied to the application and to where the system sits. An allowable charge limit is a function of room size. A design has to satisfy both.

For propane under the air conditioner standard, that paper describes the shape precisely. Below 0.15 kilograms there is no room-size dependency at all. Above 0.15 kilograms the allowable charge climbs with floor area. It stops climbing at an upper limit of around 1 kilogram, past which a larger room permits nothing further.

Where the circuit sits moves the ceiling more than any other factor. The same summary gives roughly 1 kilogram of hydrocarbon for the part of a system indoors, against about 5 kilograms outside or inside an enclosure. Occupied space is the thing being protected. Take the refrigerant out of it and the permitted quantity multiplies.

One consequence of capping the charge is rarely stated out loud. The same paper plots cooling capacity against charge for a propane air conditioner, and the curves separate by seasonal efficiency. A higher efficiency rating needs more refrigerant to reach the same capacity, as does a larger capacity at any efficiency. So a cap on the quantity is quietly a cap on the machine, on both axes at once.

That is the honest cost of the trade, and it is why the standards work matters more than the chemistry. Nothing about propane cools badly. What limits it is a number written to keep a room below a threshold, and every kilowatt of capacity and every point of efficiency has to be found underneath that number.

Design follows the ceiling. Once the permitted quantity is tied to the room, a machine has to be engineered to need less refrigerant, or to hold it where the cap is looser. Both routes are already visible in equipment on the market.

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

Where the circuit has to come indoors, the standard trades allowance for engineering. The Green Cooling Initiative paper lists four measures. Construction tighter than standard practice. Housing shaped to disperse a leak. Guaranteed airflow so refrigerant cannot settle at floor level. Valves that limit how much of the charge can reach the room at all.

The materials change too, which is the ordinary reason a machine built for one gas will not take another. A producer sheet for propane rules out EPDM rubber, natural rubber and silicone in the circuit, and warns that polyolester oil dissolves too readily in hydrocarbons. Mineral and alkylbenzene lubricants suit it better. Seals and oil are chosen against the refrigerant, and they stay chosen.

Those measures are why the ceiling moved at all. Older formulas assumed the entire charge emptying into the room instantly, which forced the mass down. Guarantee that a release is slow or well mixed, and more refrigerant can be tolerated before the mixture reaches the threshold. Recent standards work has largely been about pricing that in.

The effect is uneven across machine types, and that is where a Singapore household comes in. The same paper sets out how much cooling propane can deliver in each kind of system. Those figures come straight out of the charge limits above.

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

Split air conditioners are the harder case, and one market got there ahead of everyone. The International Institute of Refrigeration credits India, where a manufacturer put propane split units into the local market from 2012, supported by a network of trained installers. China, Southeast Asia and South America have been converting production lines since. Beyond small and portable units, market introduction has stayed limited.

The installer network earns its place in that account. Charge limits govern what may be built. What happens on a service visit governs whether the design survives contact with the field, and a class 3 refrigerant asks more of whoever opens a circuit. Shipping the equipment without the training does half the job.

Purity is the second thing a trade has to be ready for. Producers warn that hydrocarbon refrigerant has to arrive very pure, because sulphur or water in the cylinder degrades the oil and reaches the compressor. Impure product also tends to be cut with other hydrocarbons, which shifts the physical behaviour of what goes into the circuit. That is not a tolerance the counterfeit refrigerant trade is built to respect.

Locally, the visible movement is on the commercial side. 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 well under the gas in household splits today, so those categories have to move somewhere else entirely.

For household splits here, no published instrument mentions propane at all. It clears the domestic ceiling by a wide margin, and that is a permission, not a plan. Which formats manufacturers choose to engineer, what the standards allow in the room sizes an HDB flat actually has, and whether the trade is equipped for the servicing are three separate questions. Chemistry answers none of them.

• •Start from what your own machine holds. That answer is printed on the aircon rating plate, and it 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. Several bedrooms hanging off one condenser spread a single charge across long pipe runs, and a ceiling binds there first.
• •Discount any date you are given for propane reaching household splits in Singapore. No published instrument sets one, and no schedule implies one.
• •Judge a technician on whether they know which class the gas in front of them belongs to. That question separates more people than any certificate does.