Natural refrigerants, explained.

Natural refrigerants are gases used in cooling and heating applications (and in foam-blowing and propellants) as an environmentally friendly alternative to laboratory-developed halogenated refrigerants, which use chlorine and/or fluorine. (Fluorinated gases are often called f-gases.) Natural refrigerants are found in nature and consequently do not damage the environment upon escaping into the atmosphere. By contrast, halogenated refrigerants, upon escaping into the atmosphere, deplete the ozone layer (CFCs and HCFCs), contribute to global warming (CFCs, HCFCs and HFCs) or add to PFAS pollution (some HFOs and HFCs). Natural refrigerants have none of those effects.

Natural refrigerants also have very favorable thermodynamic properties, making them extremely efficient gases, typically more efficient than f-gases. Because they are efficient and environmentally benign, natural refrigerants are not subject to phase downs or phase outs under government regulations; thus, they are considered future-proof. F-gases are patented while natural refrigerants are not; as a result of that and supply-demand issues, natural refrigerants are much less expensive than f-gases.

There are generally thought to be five natural refrigerants: carbon dioxide/CO₂ (R744); hydrocarbons such as propane (R290), isobutane (R600a), n-butane (R600) and propylene (R1270); ammonia (R717); water (R718); and air (R729). The most common natural refrigerants are R744, R290, R600a and R717.

Refrigerant-grade CO₂ (R744) is a byproduct of the industrial production of ammonia, alcohol and fertilizer. The gas is purified, compressed, and liquefied for use as a refrigerant. A greener way of producing CO₂ is anaerobic digestion, where organic waste is naturally broken down by bacteria in an enclosed space and without oxygen. This process produces biogas, which typically consists of 60% biomethane and 40% CO₂.

The traditional way of making ammonia (R717) is to strip hydrogen from natural gas using steam (producing CO₂ as a by-product). The hydrogen is then combined with nitrogen from the air at high pressure and temperatures of hundreds of degrees Celsius. This procedure is called the Haber-Bosch process. A greener approach is to make hydrogen by splitting water with electricity sourced from renewables; the rest of the Haber-Bosch process remains the same.

Italian-based gas manufacturer GTS produces the hydrocarbons propane (R290), isobutane (R600a), n-butane (R600) and propylene (R1270) by extracting refrigerant-grade hydrocarbons from raw liquid petroleum gas obtained from companies that own oil refineries and extractive wells. GTS has successfully tested the performance of the 1MW solar photovoltaic (PV) plant at its hydrocarbon manufacturing facility.

Global warming potential (GWP) is a way to compare the global warming impacts of different greenhouse gases (GHGs) in the atmosphere, where they absorb thermal energy and slow the rate at which this energy escapes to space. Specifically, GWP measures how much energy the emissions of 1 metric ton of a gas will absorb over a given period of time (usually 100 or 20 years), relative to the emissions of 1 metric ton of CO₂, which has a GWP of 1. The larger the GWP, the more that a gas warms the Earth compared to CO₂ over that time period. While the 100-year GWP is the most common measure, the 20-year GWP is gaining increasing usage as a more relevant measure of climate impact and is the standard still used by New York State in its f-gas regulations. (The GWPs listed here are from the IPCC’s AR6 listing in 2021.)

F-gases have traditionally had extremely high GWPs relative to CO₂. R12, the most popular CFC, has a 100-year GWP of 12,500 and a 20-year GWP of 12,700 in addition to depleting the ozone layer; thus, it is 12,700 times as powerful as CO₂ in warming the Earth over 20 years. R22, the most popular substitute for R12, has a 100-year GWP of 1,960 and a 20-year GWP of 5,690 in addition to also depleting the ozone layer.

The replacements of ozone-depleting gases, HFCs, do not deplete the ozone layer (as required by the Montreal Protocol treaty enacted globally in 1987), but they still possess very high GWPs. Thus, HFCs R134a, R32, R404A and R410 have GWPs (100 year/20 year) of 1,530/4,140, 771/2,690, 4,728/7,208 and 2.255/4,715, respectively. As a result, HFCs are being phased down globally per the Kigali Amendment to the Montreal Protocol.

The latest iteration of f-gases, HFOs, have very low GWPs (both 100- and 20-year), such as 0.501 (100-year) and 1.81 (20-year) for the commonly used HFO-1234yf; however, HFO-1234yf is a PFAS and converts 100% in the atmosphere over about 12 days into trifluoroacetic acid (TFA), another PFAS, which descends in rain.

The GWPs (both 100- and 20-year) of natural refrigerants are very low: 1 for CO₂, less than 1 for propane and isobutane, and zero for ammonia, water and air.

In the 1970s, scientists discovered the depletion of ozone in the stratosphere, which created a hole in the ozone layer around Earth’s polar regions. The main cause of ozone depletion and the ozone hole was found to be the escape into the atmosphere of halogenated refrigerants CFCs (such as R11 and R12) and HCFCs (notably R22). Once in the stratosphere, their chlorine atoms catalyze ozone (O₃) into oxygen (O₂). These are ozone-depleting substances (ODS).

The ozone layer limits the amount of ultraviolet light that can pass through the Earth’s atmosphere, thereby preventing skin cancer, sunburn, cataracts and other ailments. To protect the ozone layer, virtually all nations in 1987 passed the Montreal Protocol, which bans CFCs, HCFCs and other ozone-depleting chemicals. Since then the ozone hole has begun to close, though it has many decades to go.

The ozone-depletion potential (ODP) measures the amount of damage a substance does to the ozone layer, relative to that of CFC-11, which is given an ODP of 1. R22 has an ODP of 0.04, according to the WMO (World Meteorological Organization), as of 2011. Natural refrigerants have a zero ODP.

Per- and polyfluoroalkyl substances (PFAS) are a group of more than 14,000 synthetic chemicals that have been used in consumer products around the world since the 1950s. They are commonly used to prevent food from sticking to packaging or cookware, make clothes and carpets resistant to stains, improve firefighting foam, among numerous other applications. Many f-gases such as HFC-134a and HFO-1234yf are also PFAS according to the widely accepted and scientifically endorsed definition published by the OECD (Organisation for Economic Co-operation and Development) in 2021. Under this definition, supported by more than 150 PFAS scientists and used throughout the world, PFAS essentially includes “at least one fully fluorinated carbon atom.” (The U.S. Environmental Protection Agency does not use this definition, though many U.S. states do.)

This definition also covers trifluoroacetic acid (TFA), which is formed by some f-gases when they leak into the atmosphere. Notably, HFO-1234yf, used in car air-conditioning and many refrigeration blends, breaks down 100% into TFA over about 12 days; the TFA comes down to Earth in rainfall, infiltrating waterways and land throughout the world.

PFAS molecules include carbon linked to fluorine atoms.

Because the carbon-fluorine bond is one of the strongest, PFAS are extremely durable and have been dubbed “forever chemicals.” A key feature in PFAS is the number of carbon atoms it has. The first PFAS to be found, PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid), have eight carbon atoms. TFA has two carbon atoms and is categorized as an ultrashort-chain PFAS.

While the decomposition of f-gases is considered the largest generator of TFA, other chemicals, such as certain pesticides and pharmaceuticals, also degrade into TFA, making it the most prevalent PFAS in the environment.

Natural refrigerants are very efficient due to their thermodynamic properties.

Ammonia is well-known to be an extremely energy-efficient refrigerant. According to the IIAR (International Institute for All-Natural Refrigeration), ammonia is 3–10% more efficient than competitive refrigerants; as a result ammonia systems use less electricity.

Hydrocarbons like propane are also highly efficient. According to Carel, the latent heat of vaporization of propane is almost two times higher than that of the most common HFC refrigerants: this means a higher cooling/heating effect for the same refrigerant mass flow.

Early transcritical CO₂ booster systems ran less efficiently than f-gas systems in warm climates. However, that issue was resolved by the development of technologies that increase the efficiency of CO₂ like adiabatic gas coolers, ejectors, parallel compression, subcooler systems, and Epta’s FTE and ETE technologies. Depending on a store’s geographic location, source of power (e.g., utility power cost) and degree of implementation of technological advances, a supermarket can save on average 5% to 18% on energy bills with transcritical CO₂ compared with a traditional commercial refrigeration systems, according to Hillphoenix. In addition, taking into account the robust heat reclaim offered by CO₂, transcritical systems become highly efficient and save end users a considerable amount of energy.

Isobutane was first used in residential fridges in the 1990s and is now present in billions of these units worldwide, including now in the U.S.

Commercial refrigeration is probably the application where natural refrigerants have been most widely employed. ATMOsphere research showed that, as of December 2025, 106,000 stores in Europe, 5,120 in North America and 14,350 (13,500 convenience stores) in Japan were using transcritical CO₂ refrigeration, while millions of self-contained propane units were also installed in stores worldwide. In Europe, transcritical CO₂ has become the primary refrigeration system for new and remodeled stores, with some stores using only propane cases.

Ammonia has been the dominant refrigerant for industrial refrigeration (cold-storage and food processing) for more than 100 years, with low-charge central and packaged systems emerging in recent years to improve safety and reduce regulatory oversight. Over the past five years, transcritical CO₂ refrigeration has become an increasingly viable and popular natural option for industrial applications that want to avoid ammonia. In Europe there were 4,100 industrial sites using low-charge ammonia systems and 5,650 using transcritical CO₂ as of December 2025, according to ATMOsphere research. In North America, the numbers were 1,480 for low-charge ammonia and 1,240 for transcritical CO₂.

In Europe, CO₂, propane and ammonia chillers are widely used for process cooling in the food and beverage industry, while in the U.S., these chillers are increasingly being employed.

CO₂, ammonia and propane can all be used in heat pumps in a variety of applications. For example, CO₂ is employed in many hot-water heat pumps, both residential (especially in Japan) and commercial. In Europe, CO₂ heat pumps are capable of generating space heat and domestic hot water. CO₂ is also seen in large heat pumps supporting district heating as well as in industrial process applications.

Ammonia is a well-known refrigerant used in large-capacity heat pump systems for industrial applications and district heating.

Propane is increasingly seen in outdoor monobloc residential heat pumps in Europe deployed for space heating and hot water generation. In the U.S., efforts are underway to raise the charge limit of propane for monobloc residential heat pumps.

Air-conditioning is an application with a relatively small percentage of natural refrigerant installations, but has great potential for growth. Chillers using CO₂, propane or ammonia are being used for comfort cooling in commercial settings. And there is a small but growing market in Asia and Europe for split ACs using propane. As with heat pumps, in the U.S., the charge limit for propane has to be raised for this application to become available.

ATMOsphere research has determined that as of December 2025 there were approximately 27,000 commercial propane chillers and heat pumps installed in Europe, along with 1,000 commercial CO₂ chillers and heat pumps.

In Europe, a small but growing market for CO₂-based heat pumps, which provide comfort cooling and heating, is developing for electric vehicles from manufacturers such as Volkswagen and Ford; Volkswagen has sold more than 1.5 million vehicles with a CO₂ MAC system. Manufacturer ZF is offering an electric vehicle with a propane heat pump. Overall, manufacturers of plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) are moving toward opting for natural refrigerants like CO₂ or propane.