Water heating accounts for 10 to 20 percent of energy use in a typical American home, making it one of the largest single energy expenses for most households. Heat pump water heaters efficient hot water through heat transfer technology have emerged as a leading solution for reducing both energy consumption and carbon emissions. These appliances use a vapor-compression cycle similar to that found in air conditioners, heat pumps, and dehumidifiers. By capturing heat from surrounding air and transferring it to the storage tank, heat pump water heaters achieve efficiencies three or more times higher than conventional electric resistance units.
Like all vapor-compression systems, heat pump water heaters rely on refrigerants to absorb and release heat. The most common refrigerant used in these units today, R-134a, is a hydrofluorocarbon (HFC) with a global warming potential roughly 1,430 times that of carbon dioxide over a 100-year period. Only a small fraction of the refrigerant in consumer appliances is captured during repairs or at end of equipment life; the rest eventually leaks into the atmosphere. Maximizing the climate benefits of heat pump water heaters means finding a replacement for R-134a. Three candidates stand out: R-513A, R-290 (propane), and R-744 (carbon dioxide).
R-134a has served the industry well, but its high GWP makes it a target for phasedown under the Kigali Amendment to the Montreal Protocol and the American Innovation and Manufacturing (AIM) Act. Heat pump water heaters a complete guide to free hot water cooling and dehumidification explores the broader benefits of these appliances. The EPA is implementing stepped reductions in HFC production, and R-134a is squarely in the crosshairs.
R-513A: A Drop-In Transition Refrigerant
R-513A is a blend of R-134a and a hydrofluoroolefin (HFO) called R-1234yf. It was designed as a near-drop-in replacement for R-134a in many applications, including centrifugal chillers, medium-temperature refrigeration, and heat pump water heaters. Its GWP of approximately 573 is roughly 60 percent lower than that of R-134a, a substantial improvement that does not require a complete redesign of the refrigeration system.
Fhb podcast segment all about heat pump water heaters discusses the practical aspects of transitioning to newer refrigerant blends. Because R-513A has similar pressure-temperature characteristics to R-134a, manufacturers can often use the same compressor, expansion valve, and heat exchanger designs with minimal modification. This lowers the barrier to adoption and allows existing production lines to pivot more quickly on a compressed timeline.
The trade-off with R-513A is that it is still a transitional solution. While its GWP is far lower than R-134a, it remains significantly higher than natural refrigerants like propane or CO₂. The HFO component, R-1234yf, breaks down in the atmosphere into trifluoroacetic acid, a persistent compound that can accumulate in water bodies. The long-term ecological impact of widespread HFO use is still under study, and some researchers call for more caution in adopting these chemicals at scale.
| Refrigerant | Type | GWP (100-yr) | Flammability | Status in HPWHs |
|---|---|---|---|---|
| R-134a | HFC | 1,430 | None (A1) | Current standard, being phased down |
| R-513A | HFC/HFO blend | 573 | None (A1) | Available in some models |
| R-290 | Hydrocarbon (propane) | 3 | High (A3) | Emerging in Europe and Asia |
| R-744 | Natural (CO₂) | 1 | None (A1) | Available in split systems |
R-290: Propane as a High-Efficiency Natural Refrigerant
R-290, more commonly known as propane, is a hydrocarbon refrigerant with a GWP of just 3, making it one of the most climate-friendly options available. Its thermodynamic properties are excellent for heat pump water heater applications, often delivering higher coefficient of performance than R-134a in the same system. Propane is also inexpensive, widely available, and compatible with mineral oil lubricants, which simplifies system design.
The single biggest obstacle to adopting R-290 is its flammability. Propane is classified as A3 under ASHRAE Standard 34, meaning it is highly flammable. This triggers safety requirements under building codes and equipment standards. In the United States, the EPA’s SNAP program has approved R-290 for retail food refrigeration and some residential applications, but adoption in heat pump water heaters has been slower due to charge size limits. Current UL and IEC standards limit the propane charge to under 150 grams in occupied spaces without additional ventilation or leak detection, and a typical heat pump water heater may require 200 grams or more to operate efficiently.
European and Asian manufacturers have moved faster on R-290. Several models sold in Europe use propane with charge sizes carefully optimized to stay within regulatory limits. Water heater selection and installation tank type tankless and heat pump water heaters for residential applications covers the broader landscape of available technologies. The International Electrotechnical Commission is currently reviewing proposals to increase the allowable propane charge limit, which would open the door to wider adoption in North America.
R-744: Carbon Dioxide for Higher Output Temperatures
R-744, or carbon dioxide, is a natural refrigerant with a GWP of 1, making it essentially climate-neutral from a direct emissions perspective. Its real advantage lies in the transcritical cycle, which delivers much higher water outlet temperatures than conventional refrigerants. While an R-134a system typically heats water to about 140°F, a CO₂-based system can produce water at 175°F or higher, suiting larger storage tanks and commercial applications.
The transcritical CO₂ cycle differs from subcritical cycles used with R-134a or R-513A. Because CO₂ has a low critical temperature of 88°F, the gas cooler operates above the critical point, meaning there is no condensation phase. Instead of a condenser, CO₂ systems use a gas cooler where the refrigerant releases heat without changing phase. This requires higher operating pressures of 1,300 to 1,800 psi compared to 200 to 300 psi for R-134a, necessitating stronger components and more robust safety certifications. Do heat pumps work in cold climates a technical analysis of cold climate heat pump performance examines how different systems perform under challenging temperature conditions.
Despite the engineering challenges, several manufacturers have brought CO₂ heat pump water heaters to market. The SANCO₂ split system from Japanese manufacturer ECO Facility uses CO₂ refrigerant and has been available in North America for several years. These units are typically more expensive, partly due to high-pressure components and low production volumes. The advantage of higher output temperatures means that a CO₂ unit can supply more usable hot water from a smaller tank and pairs well with existing hydronic heating systems.
Safety, Codes, and the Regulatory Landscape
Each refrigerant option brings a unique safety and code compliance profile. R-513A is non-flammable and requires no special handling beyond standard refrigeration practices. R-290 demands the most stringent precautions due to high flammability. R-744 operates at extreme pressures that call for specialized training and equipment.
- R-513A installation: No special ventilation requirements beyond standard HPWH best practices. Existing R-134a service equipment works. Refrigerant recovery is still required under EPA Section 608 of the Clean Air Act.
- R-290 installation: Requires installation in a mechanical room or basement with adequate ventilation. Leak detection sensors may be required for larger charge sizes. Only certified technicians with hydrocarbon-specific training can service the system. Electrical components must be non-sparking per NEC requirements.
- R-744 installation: Requires high-pressure-rated piping and fittings. Standard flare fittings are insufficient; brazed or welded joints are often specified. Service technicians need CO₂-specific recovery equipment. Split-system configurations require careful line-set sizing to manage pressure drop.
The AIM Act directs the EPA to phase down HFC production and consumption by 85 percent by 2036, already affecting refrigerant prices. R-134a costs have risen significantly since 2022. The California Air Resources Board has adopted its own HFC reduction measures, including a ban on R-134a in new heat pump water heaters starting in 2025, effectively forcing manufacturers to switch to lower-GWP alternatives for the largest state market. Other states, including New York, Washington, and Colorado, are considering similar measures. Thermal breaks heat pump water heaters diy dense pack explores the practical trade-offs when integrating advanced water heating equipment into existing building assemblies.
| Regulation or Policy | Jurisdiction | Impact on HPWH Refrigerants | Timeline |
|---|---|---|---|
| AIM Act | United States (federal) | Phasedown of HFC production by 85% | 2022 to 2036 |
| CARB HFC Measures | California | Ban on R-134a in new HPWHs | 2025 |
| Kigali Amendment | International (140+ nations) | Global HFC phasedown schedule | 2024 to 2047 |
| EPA SNAP Rule 26 | United States (federal) | Approves R-290 and R-744 for specific uses | 2023 |
| IEC Charge Limit Review | International standards | May increase allowable propane charge | Under review |
Choosing the Right Refrigerant Path
No single refrigerant option fits every situation. R-513A offers the path of least resistance with minimal changes to existing designs and service practices, but it remains a transitional solution with a GWP still hundreds of times higher than CO₂. R-290 delivers outstanding thermodynamic performance and near-zero GWP, but its flammability imposes real constraints on installation locations and service access. R-744 achieves the lowest possible direct emissions and enables higher output temperatures, but at a cost premium and with demanding pressure requirements.
For homeowners, the near-term choice is between R-513A and R-744, since both are already available in the U.S. market. R-513A units are more affordable and easier to install, while R-744 units offer better long-term climate performance and the ability to supply higher-temperature water for backup heating or hydronic integration. As propane charge limits evolve and safety standards mature, R-290 may become a viable North American option later this decade. Regardless of which path ultimately dominates, the direction is clear: high-GWP HFCs are on their way out, and climate-smart alternatives are taking their place. Dehumidifying with heat pump water heaters separating fact from marketing provides additional real-world performance context for those evaluating these systems.