A refrigerant is a chemical substance that absorbs heat from one place and releases it somewhere else, making cooling possible in air conditioners, refrigerators, freezers, and heat pumps. It works by cycling between liquid and gas states inside a closed loop of tubing, picking up warmth when it evaporates and dumping that warmth when it condenses back into a liquid. Every cooling system you interact with, from your car’s AC to the freezer aisle at the grocery store, relies on this basic principle.
How Refrigerants Actually Cool Things
A refrigerant doesn’t create cold. It moves heat. Inside a refrigerator or air conditioner, the refrigerant flows through four stages in a continuous loop. First, it enters the evaporator (the cold side) as a low-pressure liquid mixture. The warmth from the surrounding space, whether that’s your kitchen or a room full of air, provides enough energy for the refrigerant to evaporate into a gas. That phase change from liquid to gas is what absorbs the heat. It’s the same reason sweat cools your skin: evaporation pulls energy away.
A compressor then pressurizes that gas, raising its temperature significantly. The hot, high-pressure gas flows into the condenser (the warm side, usually outside your house or on the back of your fridge), where it releases its stored heat into the outdoor air or surrounding environment and condenses back into a liquid. A small expansion valve drops the pressure again, and the cycle starts over. The refrigerant never gets “used up.” It just keeps circulating, shuttling heat from inside to outside.
What makes a substance useful as a refrigerant is its boiling point. At atmospheric pressure, many refrigerants boil below negative 40°C, which means they can absorb heat even from very cold environments. That’s why refrigeration systems can maintain freezer temperatures well below zero or pull heat from cold outdoor air for a heat pump.
Types of Refrigerants and How They’ve Changed
Refrigerants have gone through several generations, each phased out or phased down because of environmental damage caused by the previous one.
The first widely used synthetic refrigerants were chlorofluorocarbons, or CFCs. Introduced in the 1930s, they were stable, non-toxic, and non-flammable, which made them seem ideal. The most famous was R-12, commonly called Freon. By the 1980s, scientists discovered that CFCs were destroying the ozone layer, the atmospheric shield that blocks harmful ultraviolet radiation. The Montreal Protocol, an international treaty, began phasing them out in the late 1980s.
Next came hydrochlorofluorocarbons (HCFCs), like R-22, which still contained chlorine but broke down faster in the atmosphere and did less ozone damage. They served as a bridge, but the Montreal Protocol was eventually amended to phase them out too. R-22 has been banned in new equipment in the United States since 2010, and production ended in 2020.
The current dominant class is hydrofluorocarbons (HFCs). These contain no chlorine and don’t harm the ozone layer. R-410A became the standard residential air conditioning refrigerant, and R-134a became standard in car AC systems. The problem: HFCs are potent greenhouse gases. R-410A has a global warming potential (GWP) of 2,088, meaning one kilogram traps as much heat over 100 years as 2,088 kilograms of carbon dioxide. R-134a comes in at 1,430. Some commercial refrigerants are even worse: R-404A has a GWP of 3,922.
The newest generation includes hydrofluoroolefins (HFOs) and lower-GWP HFCs like R-32, which has a GWP of 675, roughly a third of R-410A’s. These are where the industry is heading.
Natural Refrigerants
Before synthetic refrigerants existed, early cooling systems used substances found in nature. Those same substances are making a comeback. Carbon dioxide (R-744), ammonia (R-717), and hydrocarbons like propane (R-290) and isobutane (R-600a) all work as refrigerants and have minimal climate impact. Propane’s GWP is just 3.3. Isobutane’s is 1, essentially the same as CO2 itself.
Ammonia is widely used in large industrial and commercial refrigeration, particularly in food processing and cold storage. Carbon dioxide is gaining ground in supermarket refrigeration systems, sometimes paired with propane in cascade systems that use one refrigerant for the low-temperature side and another for the medium-temperature side. The first supermarket in North America to use a commercial propane/CO2 cascade system has already been built. Propane and isobutane are common in household refrigerators and small commercial units, especially in Europe and increasingly worldwide.
The tradeoff is that natural refrigerants come with handling challenges. Ammonia is toxic. Propane and isobutane are flammable. CO2 operates at very high pressures. These aren’t dealbreakers, but they require careful system design.
Safety Classifications
Every refrigerant gets an alphanumeric safety rating under ASHRAE Standard 34, which communicates two things: toxicity and flammability. The letter indicates toxicity: “A” means lower toxicity, “B” means higher toxicity. The number indicates flammability: “1” means no flame propagation, “2” means mildly flammable, “2L” means mildly flammable with a slow burning velocity, and “3” means highly flammable.
- A1 (lower toxicity, non-flammable): This is the most common group for traditional HVAC refrigerants. R-410A and R-134a fall here.
- A2L (lower toxicity, mildly flammable): R-32 and many newer blends carry this rating. The “L” means they burn slowly enough to reduce explosion risk.
- B2L (higher toxicity, mildly flammable): Ammonia (R-717) sits in this category, which is why it’s typically limited to industrial settings with trained operators.
- A3 (lower toxicity, highly flammable): Propane (R-290) falls here, which is why charge sizes in consumer equipment are kept small.
Health Risks of Exposure
Refrigerants are generally safe when contained inside a sealed system, but leaks or intentional misuse can be dangerous. Breathing in refrigerant gas can cause throat and lung irritation, breathing difficulty, and throat swelling. At higher concentrations, it can trigger irregular heart rhythms and collapse. Liquid refrigerant that contacts skin or eyes can cause burns and tissue damage similar to frostbite.
The most serious risk comes from intentional inhalation, sometimes called “huffing.” Sniffing refrigerant, particularly older Freon-type products, can cause long-term brain damage and sudden death, even on a first attempt. The chemicals can sensitize the heart to adrenaline, triggering a fatal cardiac arrest with no warning.
Where Regulations Are Heading
The ozone layer is on track for near-complete recovery by the middle of this century, a direct result of the Montreal Protocol’s CFC and HCFC phaseouts. But the climate impact of their HFC replacements created a new problem, and governments are now addressing it.
In the United States, the AIM Act mandates an 85 percent reduction in HFC production and consumption from historic baseline levels by 2036. The phasedown is already underway: a 10 percent cut took effect in 2022, followed by a drop to 60 percent of baseline levels in 2024. By 2029, that falls to 30 percent. Starting January 1, 2025, restrictions took effect on using higher-GWP HFCs in new aerosols, foams, and refrigeration and air conditioning equipment.
Phasedown Schedule
- 2020 to 2023: 90 percent of baseline allowed
- 2024 to 2028: 60 percent
- 2029 to 2033: 30 percent
- 2034 to 2035: 20 percent
- 2036 and beyond: 15 percent
For homeowners, this means the next air conditioner or heat pump you buy will likely use a lower-GWP refrigerant like R-32 or R-454B instead of R-410A. Existing equipment using older refrigerants can still be serviced, but as supply tightens, costs for those refrigerants will rise. Car AC systems are transitioning too, moving away from R-134a toward alternatives with GWP values under 150.