R1234ze(E) Refrigeranttrans-1,3,3,3-Tetrafluoropropene · Very-low-GWP HFO · Chillers & heat pumps
R1234ze(E) is a single-component HFO refrigerant used in very-low-GWP chillers, heat pumps, industrial refrigeration and specialty thermal systems. Its pressure and volumetric-capacity characteristics differ from R134a, so strong performance normally comes from purpose-designed compressors, heat exchangers and controls rather than from a simple refrigerant substitution.
What is R1234ze(E) refrigerant?
R1234ze(E) is trans-1,3,3,3-tetrafluoropropene, a pure HFO with zero ODP and very low GWP. It is especially relevant to new chiller and process systems. Its formal safety classification is A2L, and its lower vapor pressure / volumetric capacity compared with R134a makes compressor and heat-exchanger optimization important.
R1234ze(E) refrigerant properties
Use these values for research and screening. Equipment design and compliance should use the property source, SDS, standard or regulation required for the specific application. Where GWP values differ between assessments, this page states the basis rather than hiding the difference.
| Property | Reference | Engineering / source note |
|---|---|---|
| Designation | R1234ze(E) / HFO-1234ze(E) | E-isomer refrigerant designation |
| Chemical name | trans-1,3,3,3-tetrafluoropropene | Single-component HFO |
| Formula | CF₃CH=CHF / C₃H₂F₄ | Honeywell technical data |
| Molecular weight | ≈ 114 g/mol | Honeywell technical data |
| Normal boiling point | −18.95°C | Honeywell technical data |
| Critical temperature | 109.4°C | Honeywell technical data |
| Critical pressure | 36.36 bar | Honeywell technical data |
| ODP | 0 | No ozone depletion |
| 100-year GWP | 1 — current EPA TT reference | Other assessment bases publish <1, ≈1.37 or older 6 |
| Safety classification | A2L | Lower toxicity / lower flammability |
| Temperature glide | None | Pure refrigerant |
| Flammability context | Some ambient tests show no limits; elevated-temperature tests can show flammability | Follow the formal A2L classification |
Scientific assessment reports, equations of state, supplier datasets and regulatory programs may use different reference years or methods. The most important practice is to identify which value the governing regulation or equipment document requires.
Where is R1234ze(E) used?
Application suitability depends on system architecture, refrigerant charge, compressor design, heat exchanger, safety classification, climate and local rules. These are established use contexts, not blanket retrofit authorization.
Centrifugal chillers
A major R1234ze(E) application in large-building, district and process cooling.
Positive-displacement chillers
EPA SNAP also recognizes R1234ze in positive-displacement chiller applications.
Industrial process refrigeration
EPA lists R1234ze(E) as acceptable subject to use conditions in new industrial-process refrigeration equipment.
Heat pumps
Purpose-designed systems can use R1234ze(E) in medium- and higher-temperature heat-pump applications.
Data-center & specialty cooling
Low-GWP chiller platforms can use R1234ze(E) where compressor and heat-exchanger design match its properties.
Heat recovery / working-fluid systems
R1234ze(E) is also considered in selected organic Rankine and thermal-recovery applications.
For broader selection research, explore the Refrigerant Database, Refrigerant Replacements and Low-GWP Refrigerants guides.
Why R1234ze(E) is not an R134a drop-in
R1234ze(E) and R134a overlap in useful refrigeration temperatures, but R1234ze(E) has lower vapor pressure and lower volumetric refrigeration capacity. A compressor selected for R134a can therefore deliver different mass flow, capacity and operating conditions with R1234ze(E).
Purpose-designed R1234ze(E) chillers can achieve strong efficiency because the compressor, heat exchangers and control strategy are optimized around the refrigerant. That does not imply a field retrofit is technically or legally approved.
For an existing R134a chiller, follow only a conversion pathway explicitly supported by the chiller and compressor manufacturer.
Understanding the A2L classification of R1234ze(E)
R1234ze(E) creates confusion because some supplier literature reports no flammability limits at typical room-temperature test conditions while the refrigerant is still classified A2L.
Honeywell literature reports no flammability limits at 21°C under one ASTM E681 test condition but a flammable range at elevated temperature under ASHRAE 34-related conditions. The engineering conclusion is to follow A2L requirements, not to relabel the refrigerant A1.
Equipment rooms, hot surfaces, charge size, ventilation, ignition sources and service operations should therefore be evaluated using the actual product standard and A2L provisions.
Why published R1234ze(E) GWP values differ
R1234ze(E) is a good example of why a refrigerant database should name the assessment basis. Older EPA SNAP chiller pages show GWP 6; Honeywell literature based on IPCC AR5 shows <1; current EPA Technology Transitions material uses 1.
Atmospheric lifetime estimates, radiative-forcing calculations and regulatory reference choices can change between scientific assessments.
For compliance, use the GWP mandated by the applicable rule. For engineering comparisons, state the assessment report and year.
R1234ze(E) vs R134a
This comparison highlights major engineering differences; it does not imply interchangeability.
| Characteristic | R1234ze(E) | R134a |
|---|---|---|
| Refrigerant family | HFO | HFC |
| Type | Single component | Single component |
| Current EPA GWP reference | 1 | 1,430 |
| Safety class | A2L | A1 |
| Normal boiling point | −18.95°C | ≈ −26.1°C |
| Critical temperature | 109.4°C | ≈ 101.1°C |
| Typical modern role | New low-GWP chillers / process systems | Large legacy installed base |
| Universal drop-in retrofit | No | No |
R1234ze(E) safety: use the A2L classification even when room-temperature tests appear nonflammable
R1234ze(E) is formally A2L. Its flammability behavior is sensitive to test temperature, which is why selected ambient tests may appear nonflammable while elevated-temperature testing shows a flammable range. Equipment and service decisions should therefore follow the A2L classification, applicable charge rules, ventilation requirements and manufacturer guidance.
Temperature-dependent behavior
Flammability observations can change with temperature; formal classification governs design.
Machinery-room concentration
Large charges can create oxygen-displacement and pressure risks even though direct GWP is very low.
Thermal decomposition
Fluorinated refrigerants can form hazardous decomposition products when exposed to flame or very hot surfaces.
Actual risk depends on refrigerant charge, pressure, release rate, room volume, ventilation, ignition sources, temperature, equipment construction, alarm logic, servicing condition and applicable codes.
See the site-wide Refrigerant Safety Guide for A1, A2L, A3 and B2L classification context.
R1234ze(E) refrigerant leak detection
Define the monitoring function before choosing the sensor
R1234ze(E) can be monitored with refrigerant-specific infrared, semiconductor or other validated sensing technologies. Fixed chiller-room monitoring should be selected for the required alarm / ventilation function, while portable service leak detectors prioritize sensitivity near joints and components. Confirm detector response to R1234ze(E), not merely to another HFO.
A portable leak locator, fixed machinery-room monitor, equipment mitigation sensor, oxygen monitor and refrigerant identifier perform different functions. Required concentration range and alarm action should be defined first.
Regulatory position of R1234ze(E) in 2026
United States
EPA SNAP lists HFO-1234ze for centrifugal and positive-displacement chillers. EPA also lists HFO-1234ze(E) as acceptable subject to use conditions in new industrial-process refrigeration. The current Technology Transitions reference GWP is 1, leaving substantial margin below many present sector GWP limits.
European Union
R1234ze(E) is a fluorinated unsaturated refrigerant and should be evaluated under the EU F-gas framework and equipment-specific placing-on-the-market restrictions. Its very low GWP helps in many applications, but later restrictions can also move some categories toward non-fluorinated solutions.
Is R1234ze(E) being phased out?
R1234ze(E) is not a high-GWP HFC being phased down in the same way as R134a. Its future position depends more on A2L product standards, fluorinated-gas policy, chemical regulation and equipment-specific technical fit.
A refrigerant can be permitted in one application, restricted in another and treated differently for new manufacture, installation, service and reclaimed material. Verify the exact equipment category and compliance date.
Use the Refrigerant Regulations Hub for region-level research.
What should be compared with R1234ze(E)?
Useful alternatives depend on the real decision: new equipment, retrofit, long-term regulation, safety class, energy efficiency, charge, climate and service capability.
Practical misconceptions about R1234ze(E)
“R1234ze(E) is A1 because it may not ignite at room temperature.”
Its formal refrigerant classification is A2L; elevated-temperature behavior is part of the classification context.
“Its GWP is definitely 6.”
That is an older SNAP reference. Current EPA Technology Transitions uses 1; other assessments publish other very-low values.
“R1234ze(E) and R1234yf are the same.”
They are different isomers with different thermophysical behavior and dominant applications.
“Any R134a chiller can be converted to R1234ze(E).”
Capacity, compressor map, controls, lubricant, approvals and safety classification must be evaluated.
R1234ze(E) refrigerant FAQ
Concise answers to common technical, service and regulatory questions about R1234ze(E).
What is R1234ze(E)?
What is the GWP of R1234ze(E)?
Is R1234ze(E) flammable?
Does R1234ze(E) have temperature glide?
Can R1234ze(E) replace R134a directly?
Where is R1234ze(E) used?
Is R1234ze(E) accepted in U.S. chillers?
Why is it attractive for chillers?
How is R1234ze(E) detected?
Is it the long-term answer for every chiller?
R1234ze(E) sources and further reading
This profile was researched against current government, standards, scientific, manufacturer and validated refrigerant-detection references. Re-check the latest edition before design, service or compliance decisions.
Working with R1234ze(E) or planning a refrigerant transition?
Compare refrigerant properties, safety class, regulatory position and leak-detection requirements before choosing an equipment pathway.
Technical Notice: This page is for refrigerant research and general technical reference. Refrigerant suitability, permitted charge, equipment approval, leak mitigation, servicing procedures and regulatory compliance depend on the exact equipment, installation and jurisdiction. Always verify current manufacturer documentation, SDS, applicable standards and local regulations before selecting, replacing, charging or servicing a refrigerant.