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Refrigerants are working fluids that transfer heat from a cold environment to a warm environment. For example, the refrigerant in an air conditioner moves heat from a cool indoor environment to a hotter outdoor environment. Similarly, the refrigerant in a kitchen refrigerator moves heat from the inside the refrigerator out to the surrounding room. A wide range of fluids are used as refrigerants, with the specific choice depending mainly upon the temperature range needed.
Refrigerants are the basis of vapor compression refrigeration systems. The refrigerant is circulated in a loop between the cold and warm environments. In the low-temperature environment, the refrigerant absorbs heat at low pressure, causing it to evaporate. The gaseous refrigerant then enters a compressor, which raises its pressure and temperature. The pressurized refrigerant circulates to the warm environment, where it releases heat and condenses to liquid form. The high-pressure liquid is then depressurized and returned to the cold environment as a liquid-vapor mixture.
Refrigerants are also used in heat pumps, which work like refrigeration systems. In the winter, a heat pump absorbs heat from the cold outdoor environment and releases it into the warm indoor environment. In summer, the direction of heat transfer is reversed.
Refrigerants include naturally occurring fluids, such as ammonia or carbon dioxide, and synthetic fluids, such as chlorofluorocarbons. Many older synthetic refrigerants are banned to protect the Earth’s ozone layer or to limit climate change. Newer synthetic refrigerants do not contribute to those problems. Some refrigerants are flammable or toxic, making careful handling and disposal essential.
In thermodynamic terms, refrigerants carry thermal energy as enthalpy, which greatly increases or decreases during evaporation or condensation. The difference between the enthalpy of the vapor and liquid phase is called the latent heat of vaporization. The latent heat of vaporization allows substantial energy to be absorbed or released, with minimal temperature change, in the evaporator or condenser. Engineers control the temperatures in the evaporator and condenser by changing the fluid’s pressure.
The operating pressures of refrigerants range from roughly 280–2,500 kPa (40–360 psi). Operating temperatures can be as low as −50 °C (−58 °F) or higher than 100 °C (212 °F). Different refrigerants work best for specific temperature intervals.
A refrigerant must achieve a boiling point below the desired temperature of the cold environment. Heat will then flow from the cold environment into the refrigerant, causing it to evaporate. The boiling point is lower if the refrigerant pressure is lower. For this reason, refrigerant in the evaporator (cold side) will have a reduced pressure.
Similarly, the refrigerant must achieve a boiling point above the temperature of the warm environment, so that heat will flow out of the refrigerant as it condenses. Since boiling point rises with increasing pressure, the refrigerant in the condenser (warm side) will have an elevated pressure.
Therefore, the first requirement of any refrigerant is to achieve the needed cold and warm temperatures within a practical range of pressure. The highest pressure used should ideally be containable by copper tubing or less expensive aluminum tubing. Extremely high pressures may require stronger and more costly tubing.
Refrigerants should also have a high latent heat of vaporization, a moderate density in liquid form, and a relatively high density in gaseous form. For most refrigeration systems, a high critical point temperature is desirable. Below the critical point, the refrigerant can condense from vapor to liquid at nearly constant temperature in the condenser. A few refrigerants, like carbon dioxide, may operate in warm environments hotter than the critical point temperature. Then, the condenser must be replaced by a gas cooler operating over a wider temperature range.
Refrigerants should be non-corrosive to the components in the system. To protect the compressor, lubricants and shaft seals compatible with the refrigerant must also be available.
Finally, an ideal refrigerant should be non-toxic and non-flammable, with no ozone depletion potential and very low global warming potential.
 | This article is missing information about the historical development of refrigerants during the 19th and early 20th centuries. (August 2025) |
Vapor compression refrigeration was invented in the early 1900s, with seminal patents filed by Oliver Evans (1805) and Jacob Perkins (1809). Ice making and meat packing were early applications. Refrigerants used during the 19th century included ethyl ether, dimethyl ether, ammonia, carbon dioxide, sulfur dioxide, and methyl chloride. Several of those refrigerants faded from use quickly, owing their flammability or toxicity. By the end of the century, ammonia had achieved a dominant position in industry.[1]
Household use of vapor compression refrigerators and air conditioners emerged in the early 20th century, with early systems using ammonia, isobutane, methyl chloride, propane, and sulphur dioxide. Each of these had drawbacks for household use, such as odor, toxicity, or flammability. (Despite their flammability, propane and isobutane had good safety records.) [1]
In 1928 Thomas Midgley Jr. invented a non-flammable, non-toxic chlorofluorocarbon gas, Freon (R-12). Freon is a trademark name owned by DuPont (now Chemours) for any chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), or hydrofluorocarbon (HFC) refrigerant. Following the discovery of better synthesis methods, CFCs including R-11,[2] R-12,[3] R-123[2] and R-502[4] dominated the market for half a century.
In the mid-1970s, scientists discovered that CFCs were causing substantial damage to the ozone layer that protects the earth from ultraviolet radiation, and to the ozone holes over polar regions.[5][6] This led to the signing of the Montreal Protocol in 1987 which aimed to phase out CFCs and HCFC[7] but did not address the contributions that HFCs made to climate change. The adoption of HCFCs such as R-22,[8][9][10] and R-123[2] was accelerated and so were used in most U.S. homes in air conditioners and in chillers[11] from the 1980s as they have a dramatically lower Ozone Depletion Potential (ODP) than CFCs, but their ODP was still not zero which led to their eventual phase-out.
The environmental organization Greenpeace provided funding to a former East German refrigerator company to research alternative ozone- and climate-safe refrigerants in 1992. The company developed a hydrocarbon mixture of propane and isobutane, or pure isobutane,[12] called "Greenfreeze", but as a condition of the contract with Greenpeace could not patent the technology, which led to widespread adoption by other firms.[13][14][15] Policy and political influence by corporate executives resisted change however,[16][17] citing the flammability and explosive properties of the refrigerants,[18] and DuPont together with other companies blocked them in the U.S. with the U.S. EPA.[19][20]
Beginning on 14 November 1994, the U.S. Environmental Protection Agency restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act.[21] In 1995, Germany made CFC refrigerators illegal.[22]
In 1996 Eurammon, a European non-profit initiative for natural refrigerants, was established and comprises European companies, institutions, and industry experts.[23][24][25]
In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change.
In 2000 in the UK, the Ozone Regulations[26] came into force which banned the use of ozone-depleting HCFC refrigerants such as R22 in new systems. The regulations also banned the use of virgin R22 as a "top-up" fluid for maintenance from 2010 and from 2015 for recycled R22.[citation needed]
Hydrofluorocarbons (HFCs) such as R-134a,[27][28] R-407A,[29] R-407C,[30] R-404A,[4] R-410A[31] (a 50/50 blend of R-125/R-32) and R-507[32][33] were promoted as replacements for CFCs and HCFCs in the 1990s and 2000s. HFCs were not ozone-depleting but did have global warming potentials (GWPs) thousands of times greater than CO2 with atmospheric lifetimes that can extend for decades. Consequently, starting from the 2010s, new equipment used hydrocarbon and HFO (hydrofluoroolefin) refrigerants including R-32,[34] R-290 (propane),[35] R-600a (isobutane),[35] R-454B,[36] R-1234yf,[37][38] R-514A,[39] R-744 (CO2),[40] R-1234ze(E)[41] and R-1233zd(E).[42] These refrigerants have an ODP of zero and a low GWP. The hydrocarbon refrigerants and CO2 are sometimes called natural refrigerants because they can be found in nature.
In 2004, Greenpeace worked with multinational corporations like Coca-Cola and Unilever, and later Pepsico and others, to create a corporate coalition called Refrigerants Naturally!.[22][43] This organization promoted the use of in natural refrigerants as alternatives to the synthetic refrigerants. Four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S.[44] It is estimated that almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.[45]
In 2006, the EU adopted a Regulation on fluorinated greenhouse gases (FCs and HFCs) to encourage to transition to natural refrigerants (such as hydrocarbons).
From 2011 the European Union started to phase out refrigerants with a global warming potential (GWP) of more than 150 in automotive air conditioning (GWP = 100-year warming potential of one kilogram of a gas relative to one kilogram of CO2) such as the refrigerant HFC-134a (known as R-134a in North America) which has a GWP of 1526.[46] In the same year the EPA decided in favour of the ozone- and climate-safe refrigerant for U.S. manufacture.[13][47][48]
A 2018 study by the nonprofit organization "Drawdown" put proper refrigerant management and disposal at the very top of the list of climate impact solutions, with an impact equivalent to eliminating over 17 years of US carbon dioxide emissions.[49]
In 2019 it was estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of direct radiative forcing from all long-lived anthropogenic greenhouse gases.[50] and in the same year the UNEP published new voluntary guidelines,[51] however many countries have not yet ratified the Kigali Amendment.
By early 2020 HFCs (including R-134a, R-404A, and R-410A) were being superseded: Residential air-conditioning systems and heat pumps were increasingly using R-32. This still has a GWP of more than 600. Other devices adopted refrigerants with almost no climate impact, namely R-290 (propane), R-600a (isobutane), or R-1234yf (less flammable, in cars). In commercial refrigeration, ammonia (R-717) and CO2 (R-744) can be used.
 | This section needs to be updated. (August 2025) |
With increasing regulations, refrigerants with a very low global warming potential are expected to play a dominant role in the 21st century,[52] in particular, R-290 and R-1234yf. Starting from almost no market share in 2018,[53] low GWPO devices are gaining market share in 2022.
| Code | Chemical | Name | GWP 20yr[54] | GWP 100yr[54] | Status | Commentary |
|---|---|---|---|---|---|---|
| R-290 | C3H8 | Propane | 3.3[55] | Increasing use | Low cost, widely available, and efficient. They also have zero ozone depletion potential. Despite their flammability, they are increasingly used in domestic refrigerators and heat pumps. In 2010, about one-third of all household refrigerators and freezers manufactured globally used isobutane or an isobutane/propane blend, and this was expected to increase to 75% by 2020.[56] | |
| R-600a | HC(CH3)3 | Isobutane | 3.3 | Widely used | See R-290. | |
| R-717 | NH3 | Ammonia | 0 | 0[57] | Widely used | Commonly used before the popularisation of CFCs, it is again being considered but does suffer from the disadvantage of toxicity, and it requires corrosion-resistant components, which restricts its domestic and small-scale use. Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. |
| R-1234yf HFO-1234yf | C3H2F4 | 2,3,3,3-Tetrafluoropropene | <1 | Widely used | Less performance but also less flammable than R-290.[52] Used in most new US vehicles by 2021. | |
| R-744 | CO2 | Carbon dioxide | 1 | 1 | In use | Was used as a refrigerant prior to the discovery of CFCs (this was also the case for propane)[1] and now having a renaissance due to it being non-ozone depleting, non-toxic and non-flammable. It may become the working fluid of choice to replace current HFCs in cars, supermarkets, and heat pumps. Coca-Cola has fielded CO2-based beverage coolers and the U.S. Army is considering CO2 refrigeration.[58][59] Due to the need to operate at pressures of up to 130 bars (1,900 psi; 13,000 kPa), CO2 systems require highly resistant components, however these have already been developed for mass production in many sectors. |
| Code | Chemical | Name | Global warming potential 20yr[54] | GWP 100yr[54] | Status | Commentary |
|---|---|---|---|---|---|---|
| R-32 HFC-32 | CH2F2 | Difluoromethane | 2430 | 677 | Widely used | Promoted as climate-friendly substitute for R-134a and R-410A, but still with high climate impact. Has excellent heat transfer and pressure drop performance, both in condensation and vaporisation.[60] It has an atmospheric lifetime of nearly 5 years.[61] Currently used in residential and commercial air-conditioners and heat pumps. |
| R-134a HFC-134a | CH2FCF3 | 1,1,1,2-Tetrafluoroethane | 3790 | 1550 | Widely used/being phased out | Most used in 2020 for hydronic heat pumps in Europe and the United States in spite of high GWP.[53] Commonly used in automotive air conditioners prior to phase out which began in 2012. |
| R-410A | 50% R-32 / 50% R-125 (pentafluoroethane) | Between 2430 (R-32) and 6350 (R-125) | > 677 | Still widely used, but slowly being phased out | Most used in split heat pumps / AC by 2018. Almost 100% share in the USA.[53] Being phased out in the US starting in 2022.[62][63] |
| Code | Chemical | Name | Global warming potential 20yr[54] | GWP 100yr[54] | Status | Commentary |
|---|---|---|---|---|---|---|
| R-11 CFC-11 | CCl3F | Trichlorofluoromethane | 6900 | 4660 | Banned | Production was banned in developed countries by Montreal Protocol in 1996 |
| R-12 CFC-12 | CCl2F2 | Dichlorodifluoromethane | 10800 | 10200 | Banned | Also known as Freon, a once widely-used chlorofluorocarbon halomethane (CFC). Production was banned in developed countries by Montreal Protocol in 1996, and in developing countries (Article 5 countries) in 2010.[64] |
| R-22 HCFC-22 | CHClF2 | Chlorodifluoromethane | 5280 | 1760 | Being phased out | A once widely-used hydrochlorofluorocarbon (HCFC) and powerful greenhouse gas with a GWP equal to 1810. Worldwide production of R-22 in 2008 was about 800 Gg per year, up from about 450 Gg per year in 1998. R-438A (MO-99) is a R-22 replacement.[65] |
| R-123 HCFC-123 | CHCl2CF3 | 2,2-Dichloro-1,1,1-trifluoroethane | 292 | 79 | US phase-out | Used in large tonnage centrifugal chiller applications. All U.S. production and import of virgin HCFCs will be phased out by 2030, with limited exceptions.[66] R-123 refrigerant was used to retrofit some chiller that used R-11 refrigerant Trichlorofluoromethane. The production of R-11 was banned in developed countries by Montreal Protocol in 1996.[67] |
| Code | Chemical | Name | Global warming potential 20yr[54] | GWP 100yr[54] | Commentary |
|---|---|---|---|---|---|
| R-152a HFC-152a | CH3CHF2 | 1,1-Difluoroethane | 506 | 138 | As a compressed air duster |
| R-407C | Mixture of difluoromethane and pentafluoroethane and 1,1,1,2-tetrafluoroethane | A mixture of R-32, R-125, and R-134a | |||
| R-454B | Difluoromethane and 2,3,3,3-Tetrafluoropropene | HFOs blend of refrigerants Difluoromethane (R-32) and 2,3,3,3-Tetrafluoropropene (R-1234yf).[68][69][70][71] | |||
| R-513A | An HFO/HFC blend (56% R-1234yf/44%R-134a) | May replace R-134a as an interim alternative[72] | |||
| R-514A | HFO-1336mzz-Z/trans-1,2- dichloroethylene (t-DCE) | An hydrofluoroolefin (HFO)-based refrigerant to replace R-123 in low-pressure centrifugal chillers for commercial and industrial applications.[73][74] |
Refrigerants are classified by several international safety regulations and, depending on their classification, may only be handled by qualified personnel due to risks associated with pressure, flammability,[75] or toxicity. Further regulations address the contribution of CFC and HCFC refrigerants to ozone depletion[76] and the contribution of HFC refrigerants to climate change.[77]
ASHRAE Standard 34, Designation and Safety Classification of Refrigerants, assigns safety classifications to refrigerants based upon toxicity and flammability.[78] ASHRAE assigns a capital letter to indicate toxicity and a number to indicate flammability. The letter "A" is lower toxicity and "B" is higher toxicity. A number indicates flammability: 1 is the least flammable, and 3 is the most flammable.[79] A1 class are non-flammable, A2/A2L class are flammable, and A3 class are extremely flammable and/or explosive. (Flammability classifications relate to situations in which refrigerants are accidentally leaked into the atmosphere, not while circulated.[80]) Similarly, a class B1 refrigerant is toxic but not flammable. Other classifications applied to refrigerants include ISO 817/5149 and BS EN 378.
In view of these risks, many refrigerants may only be handled by qualified/certified engineers for the relevant classes. In the UK, C&G 2079 is legally required for working with fluorinated gases and ozone-depleting substances[81], while C&G 6187-2 is a recognized qualification for handling hydrocarbon and flammable refrigerants (Classes A2, A2L, and A3).
Non-toxic refrigerants (A class) are used in open systems, where they are expended rather than circulated. For consumer goods, the quantity of refrigerant is generally small. In 2025, open-system examples included fire extinguishers using HCFCs or HFCs, gas dusters using HFC-152a or hydrocarbon propellants, computer rooms using HFC fire suppressants, and inhalers using HFC propellants. In addition, disposable lighters contain the class A3 refrigerant butane (R-600).
Coolant and refrigerants are found throughout the industrialized world, in homes, offices, and factories, in devices such as refrigerators, window air conditioners, central air conditioning and systems (HVAC), freezers, and dehumidifiers. When these units are serviced, refrigerant gas may be vented into the atmosphere either accidentally or intentionally. To avoid such discharge, technician training and certification programs have been developed. Mismanagement of synthetic refrigerants (such as CFCs, HCFCs, and HFCs) can deplete the ozone layer or contribute to global warming.[82]
With the exception of the natural refrigerants ammonia (R717), CO2 (R744), isobutane (R600a), propane (R290), or the hydrocarbon mixture HCR188C (R441a), it is illegal to knowingly release any refrigerants into the atmosphere under Section 608 of the United States' Clean Air Act.[83][84]
Refrigerant reclamation is the act of processing used refrigerant gas that has previously been used in some type of refrigeration loop such that it meets specifications for new refrigerant gas. In the United States, the Clean Air Act of 1990 requires that used refrigerant be processed by a certified reclaimer, which must be licensed by the United States Environmental Protection Agency (EPA), and the material must be recovered and delivered to the reclaimer by EPA-certified technicians.[85]
Refrigerants may be divided into three classes according to their manner of absorption or extraction of heat from the substances to be refrigerated:[citation needed]
The R- numbering system was developed by DuPont (which owned the Freon trademark), and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon. ASHRAE has since set guidelines for the numbering system as follows:[86]
R-X1X2X3X4
For example, R-134a has 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving 1,1,1,2-Tetrafluoroethane. R-134 (without the "a" suffix) would have a molecular structure of 1,1,2,2-Tetrafluoroethane.
The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix (e.g., "Propellant 12") for the same chemical used as a propellant for an aerosol spray, and with trade names for the compounds, such as "Freon 12". Recently, a practice of using abbreviations HFC- for hydrofluorocarbons, CFC- for chlorofluorocarbons, and HCFC- for hydrochlorofluorocarbons has arisen, because of the regulatory differences among these groups.[citation needed]
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