The short answer
Natural refrigerants such as propane (R290) and carbon dioxide occur in nature and have a very low global warming potential. R290 is efficient but highly flammable, which limits how much can be used in room-sized systems.
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As rules on high-GWP refrigerants tighten, more equipment is being designed around natural refrigerants: substances that occur in nature and have little effect on the climate if they escape. In home cooling and heating, the one you're most likely to come across is R290, which is refrigerant-grade propane.
What counts as a natural refrigerant
| Refrigerant | What it is | Global warming potential | Where it's used |
|---|---|---|---|
| R290 | Propane | 3 | Some portable units and heat pumps |
| R600a | Isobutane | Very low | Many domestic fridges and freezers |
| R744 | Carbon dioxide | 1 | Some water-heating heat pumps, commercial refrigeration |
| R717 | Ammonia | 0 | Large industrial refrigeration |
Ammonia and carbon dioxide need very different equipment from a home air conditioner: ammonia is toxic, and carbon dioxide works at very high pressures. Of the natural refrigerants, propane is the one most used in small air conditioners and heat pumps.
R290: the advantages
- Very low global warming potential. At 3, a leak has a tiny effect on the climate compared with R32 at 675.
- No ozone depletion.
- Good efficiency. Propane carries heat well, and equipment designed around it can be very efficient.
- Smaller amounts. Systems often need less refrigerant by weight than similar systems using synthetic refrigerants.
R290: the catch
Propane is highly flammable, safety class A3. Equipment designed, installed and serviced for R290 isn't unsafe, but the flammability shapes where and how it can be used.
- Safety standards limit how much R290 can be used, depending on the size of the room and how the equipment is installed.
- Those limits are why R290 is most common in portable air conditioners and in self-contained outdoor units, where the refrigerant circuit is small or stays outside. It is less common in split systems, which carry refrigerant through pipes into the room.
- Engineers working on R290 need training and tools for flammable refrigerants, and must keep sources of ignition away.
Handling and the rules
The F-gas rules in Great Britain cover fluorinated gases, and R290 isn't one. That doesn't make R290 equipment DIY work. Opening a refrigerant circuit, recovering refrigerant and working with a flammable gas all need a trained engineer, and refrigerant should be recovered rather than released.
For you, the practical points are simple. Follow the manufacturer's instructions for where a portable R290 unit can be used, keep it upright and away from sources of ignition, and have any repair involving the refrigerant done by a trained engineer.
What comes next for split systems
For small appliances, natural refrigerants are already normal: many fridges and portable units use them. For wall-mounted split systems in homes, R32 is still the usual refrigerant, largely because of the limits on how much flammable refrigerant can be used in a room.
How quickly that changes depends on how the rules develop and how manufacturers design around those limits. The direction is clear, though: rules on high-GWP refrigerants are tightening, and the industry is moving to lower-GWP options. Global warming potential explained shows how refrigerants compare.
Related guides
- Refrigerants explainedA refrigerant is the fluid that carries heat around an air conditioner, boiling to absorb it and condensing to release it. Refrigerants differ in their pressures, efficiency, flammability and effect on the climate, which is why the choice matters.
- Global warming potential explainedGlobal warming potential (GWP) compares how much a gas warms the climate with the same mass of carbon dioxide, usually over 100 years. A refrigerant's GWP shows how much harm a leak would do, and it underpins the rules on refrigerants.
- R32 refrigerantR32 is the refrigerant in most new wall-mounted systems. It carries heat efficiently, usually needs less of it than R410A, and has about a third of R410A's global warming potential. It is mildly flammable, so it's handled with specific precautions.
- Portable air conditionersA portable air conditioner is a self-contained unit on wheels that cools a room and sends the heat outside through a hose, usually out of a window. It needs no professional installation, but it is noisier and less effective than a fixed split system.