The Growing Importance of Refrigerant Choice in Ductless Air Conditioning

As ductless mini-split and multi-zone air conditioning systems become a staple in residential and commercial buildings worldwide, the conversation around their environmental footprint has intensified. While these systems are celebrated for their energy efficiency and zoned cooling flexibility, the refrigerants they rely on carry significant environmental consequences. The global push to curb climate change has placed refrigerants under a regulatory microscope, making it essential for contractors, building owners, and homeowners to understand the differences between the chemicals circulating inside their units. Choosing the right refrigerant is no longer just a technical specification—it is a direct factor in reducing a building’s contribution to global warming.

Refrigerants in ductless AC systems are responsible for moving heat from indoors to outdoors, but when leaks occur (or at end of life), they can escape into the atmosphere. The impact of these emissions depends on the chemical properties of the refrigerant. Older compounds like R-22 (a hydrochlorofluorocarbon, or HCFC) have been largely phased out due to their ozone-depleting effects, but current refrigerants like R-410A still carry a high global warming potential (GWP). Newer alternatives, including R-32, R-290 (propane), and HFO-based blends, promise much lower GWP values, but each comes with trade-offs in efficiency, safety, and system design. This article provides a detailed comparison of the most common ductless AC refrigerants, their environmental impacts, and the trends shaping the future of cooling.

Understanding the Key Environmental Metrics

Before comparing specific refrigerants, it is important to grasp the two primary metrics used to measure their environmental harm: Ozone Depletion Potential (ODP) and Global Warming Potential (GWP). A third metric, Total Equivalent Warming Impact (TEWI), provides a more complete picture by including both direct emissions from refrigerant leaks and indirect emissions from energy consumption.

Ozone Depletion Potential (ODP)

ODP measures a substance’s ability to destroy stratospheric ozone. Chlorine-containing refrigerants, such as CFCs and HCFCs (e.g., R-22), have high ODP values and were banned under the Montreal Protocol. Modern refrigerants used in ductless AC systems have zero ODP, meaning they do not deplete the ozone layer. This was a major achievement, but it shifted the focus to global warming.

Global Warming Potential (GWP)

GWP compares the amount of heat trapped by a given mass of refrigerant to the same mass of carbon dioxide (CO₂) over a 100-year period. CO₂ has a GWP of 1. Refrigerants like R-410A have a GWP of 2,088, meaning one kilogram of R-410A released into the atmosphere is equivalent to over two tonnes of CO₂. Lower-GWP refrigerants, such as R-32 (GWP 675) or R-290 (GWP 3), dramatically reduce that impact.

Total Equivalent Warming Impact (TEWI)

TEWI combines the direct effect of refrigerant emissions with the indirect effect of the energy used to run the system over its lifetime. A highly efficient system using a high-GWP refrigerant might have a lower TEWI than a less efficient system using a low-GWP refrigerant, because the indirect emissions from grid electricity often dominate. However, as power grids decarbonize, the direct refrigerant emissions become relatively more important.

Common Refrigerants in Ductless AC Systems

The ductless AC market today features several refrigerants, each with distinct characteristics. Below we examine the most widely used options, their environmental profiles, and practical considerations.

R-410A (HFC Blend)

R-410A has been the dominant refrigerant in ductless systems for over two decades. It is a blend of R-32 and R-125, with zero ODP but a very high GWP of 2,088. It operates at higher pressures than older refrigerants, which allowed manufacturers to design more compact, efficient compressors. Despite its excellent thermodynamic performance and non-flammable classification (ASHRAE A1), R-410A is being phased down globally under the Kigali Amendment to the Montreal Protocol. The European Union’s F-Gas Regulations and the U.S. EPA’s AIM Act are accelerating the transition away from high-GWP HFCs. New installations using R-410A are still permissible in many regions but are increasingly discouraged, and many manufacturers are shifting to lower-GWP alternatives.

R-32 (Pure HFC)

R-32 is a single-component refrigerant that has gained significant traction in ductless systems, especially in Japan, India, and parts of Europe. It has a GWP of 675, roughly 68% lower than R-410A, and offers better energy efficiency in many applications. R-32 is classified as mildly flammable (ASHRAE A2L), which requires specific handling and safety measures, but it has a good safety record when systems are designed properly. Because R-32 is a pure fluid, it is easier to recover and recycle than blends, and its lower GWP makes it a strong candidate for meeting future regulatory limits. Many major ductless AC brands now offer R-32 models as standard.

R-290 (Propane, Natural Refrigerant)

R-290, also known as propane, is a natural refrigerant with a GWP of just 3 and zero ODP. It has excellent thermodynamic properties, providing high energy efficiency and capacity. However, R-290 is highly flammable (ASHRAE A3), which limits its use to systems with small refrigerant charges—typically a few hundred grams. In ductless AC, that constraint often restricts R-290 to smaller split units or portable systems. Regulatory standards like IEC 60335-2-40 and UL 484 allow higher charge limits under strict safety conditions, but adoption remains limited in larger ductless applications. Nonetheless, R-290 is widely used in refrigeration and is growing in the AC market as safety standards evolve.

R-1234yf (HFO)

R-1234yf is a hydrofluoroolefin developed primarily for automotive air conditioning but has been adapted for stationary applications. It has an extremely low GWP of 4 and zero ODP. R-1234yf is mildly flammable (A2L) and has thermodynamic properties similar to R-134a. In ductless AC, it is sometimes used in blends (e.g., R-454B) rather than as a pure refrigerant. While R-1234yf is not yet widespread in ductless systems, it is part of the next generation of low-GWP alternatives. Concerns about its long-term environmental degradation products (like trifluoroacetic acid) are being studied, but it is generally considered a major improvement over HFCs.

R-454B (HFC/HFO Blend)

R-454B is a blend of R-32 and R-1234yf, designed as a drop-in replacement for R-410A in many ductless and ducted systems. It has a GWP of around 466, a 78% reduction from R-410A. R-454B is mildly flammable (A2L) but offers performance close to R-410A. Several major HVAC manufacturers are adopting R-454B for future product lines. It combines the efficiency of R-32 with the very low GWP contribution from R-1234yf.

R-32 / R-410A Comparison Table (for reference)

  • GWP: R-410A = 2,088; R-32 = 675
  • Flammability: R-410A = A1 (non-flammable); R-32 = A2L (mildly flammable)
  • Efficiency: R-32 often 5-10% higher SEER in optimized systems
  • Charge size: Typically 10-20% less refrigerant required with R-32
  • Regulatory outlook: R-410A being phased down; R-32 widely accepted

Environmental Impact in Detail

Direct Emissions: Leaks and Service

The largest direct environmental impact from a ductless AC system comes from refrigerant leaks during operation, maintenance, and end-of-life disposal. A 2018 study by the Lawrence Berkeley National Laboratory estimated that average annual leakage rates for ductless mini-splits range from 3% to 8% of the total charge. Over a 15-year lifespan, a 3-ton system charged with R-410A (approx. 3.5 kg refrigerant) could release the equivalent of over 6 tonnes of CO₂ through leaks alone. Switching to R-32 reduces that warming impact by nearly 70%, while R-290 reduces it by over 99%.

Indirect Emissions: Energy Efficiency

Refrigerant choice also influences system energy efficiency. R-32 and R-290 both offer superior thermodynamic properties compared to R-410A, resulting in higher COP (coefficient of performance) in many conditions. A more efficient system consumes less electricity, reducing indirect CO₂ emissions from power plants. According to a 2020 report by the Japan Refrigeration and Air Conditioning Industry Association (JRAIA), R-32 systems achieve SEER values up to 12% higher than comparable R-410A models. Over the system life, these energy savings can double the overall greenhouse gas reduction compared to just lowering GWP alone.

End-of-Life and Reclamation

Improper disposal of ductless AC units often leads to the venting of refrigerant into the atmosphere. Regulations under the U.S. Clean Air Act and similar laws in other countries require recovery and recycling, but enforcement remains inconsistent. Low-GWP refrigerants like R-290 and R-32 are easier to recover and reuse because they are single-component fluids, whereas blends like R-410A and R-454B can change composition if partially leaked, making reclamation less effective. Investing in proper recovery equipment and training technicians in low-GWP handling is critical to minimizing end-of-life emissions.

Regulatory Landscape and Phase-Down Schedules

International and national regulations are driving the shift away from high-GWP refrigerants. The Kigali Amendment to the Montreal Protocol requires a phasedown of HFCs, with developed nations cutting consumption by 85% by 2036. The United States implemented this through the AIM Act, which mandates an 85% reduction in HFC production and use by 2036. The European Union’s F-Gas Regulation sets even stricter targets, banning the use of refrigerants with a GWP above 750 in new stationary air conditioning equipment from 2027 (with some exceptions).

These regulations effectively phase out R-410A for new installations in many markets. R-32 (GWP 675) and R-454B (GWP 466) both meet the EU threshold and are widely accepted in the U.S. under EPA’s SNAP program. R-290 is allowed in small charges (up to 1.5 kg in some regions) for residential use, subject to safety standards. Contractors and specifiers should check local building codes and environmental regulations before selecting refrigerants.

Safety Considerations for Low-GWP Refrigerants

The primary safety concern with lower-GWP alternatives is flammability. R-32 and R-454B are classified as A2L (mildly flammable with a low burning velocity), while R-290 is A3 (highly flammable). A2L refrigerants can be used in most applications with minimal additional precautions—standard ventilation and leak detection are usually sufficient. A3 refrigerants require more stringent measures: maximum allowable charge limits, use in well-ventilated areas, and prohibition in systems connected to indoor units in sleeping areas (unless specifically designed).

Despite the risks, millions of R-32 systems have been installed globally without major incidents. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has updated its Standard 34 to include A2L classification, and building codes are evolving to accommodate these refrigerants. Training technicians in proper handling, labeling, and leak detection is essential to maintain safety as the industry transitions.

Lifecycle Cost and Environmental Payoff

Switching to a low-GWP refrigerant like R-32 or R-290 can reduce a ductless AC system’s total carbon footprint by 30-80%, depending on the existing refrigerant and energy efficiency gains. The upfront cost of modern low-GWP systems is comparable to R-410A models—sometimes slightly higher due to new components (e.g., electronic expansion valves, R-32 compatible compressors), but this premium is often recovered within a few years through lower electricity bills. A lifecycle analysis published by the International Institute of Refrigeration found that R-290 systems in small units have the lowest total equivalent warming impact among available options, with a break-even period of less than five years.

  • Ultra-low GWP HFO/HFC blends: New blends like R-466A (non-flammable, GWP 675) and R-471A (GWP <150) are being developed to match R-410A performance without flammability.
  • Natural refrigerants expansion: Larger safe R-290 charges (up to 5 kg) are being considered in revised international standards, which could open up multi-split ductless systems to propane.
  • CO₂ (R-744) in ductless: While currently used mainly in commercial refrigeration, transcritical CO₂ systems could appear in specialized ductless applications in the future, offering GWP of 1.
  • Smart leak detection: Integration of refrigerant sensors and electronic leak detection in ductless units can reduce emission rates, making even high-GWP refrigerants less harmful if used temporarily before transition.
  • Circular economy for refrigerants: Mandatory refrigerant management programs and reclamation infrastructure improvements will make it easier to reuse refrigerants, reducing demand for virgin production.

Practical Guidance for Decision-Makers

For homeowners purchasing a new ductless AC, selecting a model using R-32 or R-454B is the best available choice today—balancing low GWP, high efficiency, and reasonable safety. For commercial projects, consider multi-split systems with R-32 or evaluate the feasibility of small independent units using R-290. Always work with certified technicians who follow recovery procedures and understand the specific requirements of the refrigerant in use.

For contractors and installers, investing in training for A2L and A3 refrigerants is not optional; it is a business imperative as R-410A declines. The U.S. EPA’s Significant New Alternatives Policy (SNAP) program provides up-to-date lists of acceptable and unacceptable refrigerants for each end-use. Refer to it regularly.

Conclusion

The refrigerants used in ductless air conditioning systems have a profound and direct impact on the climate. While R-410A served the industry well for many years, its high GWP makes it incompatible with global climate goals. The transition to lower-GWP alternatives like R-32, R-454B, and natural refrigerants such as R-290 is not just a regulatory requirement—it is an environmental necessity. By choosing systems with lower GWP, ensuring proper handling and recovery, and staying informed about evolving regulations, stakeholders across the supply chain can significantly reduce the cooling sector’s contribution to climate change. The technology is available, the economics are favorable, and the planet demands it.