The short answer
A 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.
On this page
Every air conditioner and heat pump relies on a refrigerant: a fluid sealed inside the pipes that moves heat from one place to another. It isn't used up, so a system in good condition shouldn't need topping up. Which refrigerant a system uses shapes how it's designed, how engineers handle it, and what happens if it ever leaks.
What a refrigerant does
A refrigerant is chosen because it boils at a very low temperature. Inside the sealed circuit the compressor controls its pressure, so it can be made to boil in one coil and condense in the other.
- In the cold coil, it boils and absorbs heat from the air passing over the fins.
- The compressor squeezes the vapour, raising its pressure and temperature.
- In the hot coil, it condenses and gives that heat up to the air.
- An expansion device drops the pressure again, ready for the next loop.
The refrigeration cycle, step by step goes through each stage in detail.
What makes a good refrigerant
No refrigerant is perfect, so designers balance several properties.
| Property | Why it matters |
|---|---|
| Boiling point and pressure | Sets the pressures the pipes and compressor must handle |
| Heat carried per kilogram | Affects efficiency and how much refrigerant a system needs |
| Flammability | Decides safety rules, including how much can be used for a room |
| Ozone depletion | Older refrigerants damaged the ozone layer and have been phased out |
| Global warming potential | How strongly a leak warms the climate compared with carbon dioxide |
Refrigerants are named with an "R" number, such as R32 or R410A. Some are single substances; others, including R410A, are blends of two or more.
The main families
Refrigerants have changed over the decades as their effects on the environment became clear.
- CFCs, such as R12, were used in older equipment. They damage the ozone layer and were phased out under an international agreement, the Montreal Protocol.
- HCFCs, such as R22, did less damage to the ozone layer but still some, and have been phased out too.
- HFCs, such as R410A and R32, don't harm the ozone layer, but many have a high global warming potential, so their use is being reduced.
- HFOs are newer synthetic refrigerants with a very low global warming potential. Many are mildly flammable.
- Natural refrigerants, such as propane (R290) and carbon dioxide (R744), occur in nature and have a very low global warming potential. Some are flammable, and some work at very high pressures.
Most new wall-mounted systems for homes use R32, an HFC with a much lower global warming potential than the R410A it replaced.
Safety classes
Every refrigerant has a safety class made of a letter and a number. The letter describes toxicity: A means lower toxicity. The number describes flammability, from 1 for no flame spread, through 2L for mildly flammable, to 3 for highly flammable.
| Class | Meaning | Example |
|---|---|---|
| A1 | Lower toxicity, no flame spread | R410A |
| A2L | Lower toxicity, mildly flammable | R32 |
| A3 | Lower toxicity, highly flammable | R290 |
A flammable refrigerant isn't unsafe in equipment designed, installed and serviced for it. It does mean safety standards limit how much can be used for a given room, and engineers follow specific procedures when they work on it.
Why refrigerants are regulated
Many refrigerants stay in the air for years once released, warming the climate far more strongly than carbon dioxide. That's why refrigerant must never be vented: when a system is repaired or removed, a qualified engineer recovers it. In Great Britain, installing, servicing or dismantling equipment that contains F-gas refrigerants needs the right F-gas qualification, and the business doing the work needs a company F-gas certificate. F-gas rules for homeowners explains what that means for you.
Related guides
- The refrigeration cycle, step by stepRefrigerant boils in a cold coil, taking in heat; a compressor squeezes the vapour, making it hot; it condenses in a second coil, giving the heat away; and an expansion valve drops its pressure so it can boil again.
- 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.
- 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.
- Natural refrigerants and R290Natural 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.