R744 and R134a are both used in refrigeration and air conditioning systems, but their operating conditions are different. Confusing them or attempting to replace them can cause serious system damage. You should compare performance, cost, and regulations. In this guide, I will give you a clear guide to help you select the right refrigerant for your system.
Differences Between R744 and R134a
R744 and R134a differ significantly in physical properties. To choose the right refrigerant, you should understand its characteristics under different conditions.
What is R744?
R744 is a natural refrigerant with pure carbon dioxide (CO₂). It operates under a wide range of pressures and temperatures. It is naturally present in the atmosphere and has a very low environmental impact, a GWP of 1, and an ODP of 0. It is widely used as a low-GWP refrigerant.
What is R134a?
R134a is one of the most widely used HFC refrigerant compounds. It has a high Global Warming Potential (GWP) of 1430, making it more harmful to the environment than R744.
R744 vs R134a: Comparison Table
Here are the characteristics differences between R744 and R134a:
| Characteristics | R744 | R134a |
| Content | CO2 | C2H2F4 |
| GWP | 1 | 1430 |
| ODP | 0 | 0 |
| Molar mass(kg/kmol) | 44.01 | 102.03 |
| Normal boiling point(°C) | -78.4 | -26.3 |
| Critical pressure(bar) | 73.8 | 40.6 |
| Critical temperature (°C) | 31.1 | 101.1 |
| Critical density(kg/m3) | 467.6 | 511.9 |
| ASHRAE Standard– Safety classification | A1 | A1 |
Differences in Performance Between R744 and R134a
Efficiency
System efficiency depends mainly on operating conditions and refrigerant properties. R744 can deliver equal or higher efficiency in properly designed commercial refrigeration and heat pump systems. However, performance depends heavily on climate conditions and system design.
R744
Operating conditions: It works best in low-temperature applications and heat rejection in cooler climates.
Performance
It offers strong heat transfer performance and high volumetric cooling capacity. These properties are beneficial for the efficiency of R744 refrigerant.
In transcritical mode, when the ambient temperature exceeds 35 ℃, the coefficient of performance (COP) of R744 will decrease. At this point, you need system optimisation, such as gas cooler pressure control.
R134a
Operating conditions: Its working temperature ranges from -10 ℃ to 40 ℃.
Performance
It performs well in medium temperature ranges and is widely used in conventional systems.
System Implications
System design differs significantly between R744 and R134a. Here’s how they compare in real-world system design:
| Property | R744 (CO₂) | R134a |
| Operating Pressure (High Side) | 80–120+ bar | 10–15 bar |
| Oil Compatibility | POE or polyalkylene glycol (PAG) | Polyolester (POE) oils |
| Leak Detection | Specialised infrared or ultrasonic detectors are required
cannot be detected by standard halogen sniffers |
Electronic or dye-based |
| System Complexity | Needs high-pressure safety valves, burst discs, reinforced piping, and dedicated controls | Mature, widely supported components |
Note: CO2 systems require oil management and optimised system design.
Differences in Regulations and Restrictions Between R744 and R134a
Due to the environmental impact of most refrigerants, some regions have established relevant legal regulations and usage restrictions on the use of refrigerants.
R744
R744 refrigerant does not require you to apply for the ARCTick refrigerant processing license or refrigerant trading authorisation. It is also not subject to the Section 608 venting prohibition. While it is not regulated like HFC, you should still follow Section 609 regulations, such as using certified refrigerant treatment equipment.
R134a
Global Regulations
The Montreal Protocol (1987): This protocol phased out CFC refrigerants such as R12 and allowed R134a refrigerant to replace R12 refrigerants.
The Kigali Amendment (2016): It gradually reduces the emissions of HFC compounds in 197 countries. The goal is to reduce emissions of HFC compounds by 80% by 2047.
EU
F-Gas Regulation (2017): It prohibits the use of R134a in new passenger vehicles.
United States
Starting from 2025, the EPA’s SNAP will restrict the use of R134a in new retail food refrigeration equipment.
In the SAE J2843 standard, maintenance personnel need to recover and recycle R134a refrigerant in automotive servicing.
China and Other Countries
In China, Canada, Australia, and Japan, these countries are phasing out R134a refrigerant and starting to use low-GWP alternatives gradually.
Differences in Costs Between R744 and R134a
The cost of using R744 refrigerant is much higher than that of R134a in the early stage. If you can handle the cost to support your use of R744 for 10-15 years, then you will achieve lower long-term operating costs in many commercial refrigeration applications.
For example:
In 2023, a lifecycle analysis by the US Department of Energy showed that supermarket systems using R744 refrigerant achieved returns within 6.2 years with a 40% increase in upfront capital compared to R134a.
Here’s what you should expect in terms of cost:
Professional tools: R744 refrigerant requires certified leak detectors and high-pressure gauges. They cost approximately $3200-$5800.
Labour cost: Installation and servicing costs are generally higher because technicians need training for high-pressure CO₂ systems.
Purchase cost: The purchase cost of R744 is much lower than that of R134a. CO2 is widely available and low-cost as a commodity gas. R744 is generally much less expensive per kilogram than R134a because carbon dioxide is widely available as an industrial gas.
Due to the relevant laws restricting the use of R134a refrigerant in different regions, the number of manufacturers of R134a has declined. This makes R134a increasingly difficult to source. With less R134a in the market, prices of R134a are expected to keep rising. Regulatory phase-down programs have increased the long-term cost pressure on R134a in many markets.
Advantages and Disadvantages of R744 vs R134a
Advantages
R744
- Good heat transfer performance
- Environmental protection (low GWP)
- Potentially lower lifecycle cost in large commercial systems
- Non-corrosive
R134a
- Availability of components
- Tested and accepted refrigerant
- Safe operating pressure
- Widely available and cost-Effective
Disadvantages
R744
- Operating at a higher pressure than traditional refrigerants
- Because of its high operating pressure, leak management and system monitoring are more demanding
- High system cost
- Strict control of moisture, oil, and other pollutants is required
- Requiring professional system design and trained technicians
- Performance may decrease in extremely hot weather without optimisation
R134a
- High GWP value
- Limited long-term availability
- High price in the medium term
- Regulatory restrictions
- Inefficiency
- Requires special management
Differences in Applications of R744 vs R134a
R744 and R134a are used in many fields. You should choose based on your application requirements. Common applications of R744 and R134a include:
R744
- Transcritical supermarket rack systems
- Low-temperature food processing lines
- Transport refrigeration
- Heat pump systems for hot water production
- Mobile air conditioning
R134a
- Automotive air conditioning
- Household refrigerators and freezers
- Supermarket display cases and beverage coolers
- Used in industrial cooling systems
- Applied in medical freezers
- Fire suppression systems
- Heat pumps
To Wrap Up
The refrigerant you choose will affect your system performance, operating costs, and legal requirements. So you should consider both GWP and long-term operating costs. For decades, R134a has been used reliably, but its serious impact on global warming makes it unsustainable to rely on.
If you are planning to replace R134a, start evaluating alternatives now. R744 is a good solution in many applications. If you still have any questions about R744 or R134 refrigerants, please consult a qualified HVAC professional.
FAQ
Can I mix R134a and R744 to ease the transition?
No. It violates the EPA Clean Air Act Section 608 and ASHRAE Standard 15. Under any operating conditions, R744 cannot be mixed with R134a, which can cause unpredictable structural changes in the system. Even trace pollution (≥ 0.5%) can void the warranty coverage and render safety certification ineffective.
Is R744 better than R134a?
It depends on your application. If you need a future-proof and greener solution, R744 is better than R134a. If you want to save money and a simpler system, R134a may still work in the short term.
Why is R134a being phased out?
R134a has a high Global Warming Potential (GWP), which contributes to climate change. Because of this, many countries are reducing or banning their use.
Does R744 require special equipment?
Yes. R744 systems operate at much higher pressure than traditional refrigerants. You need high-pressure safety valves, burst discs, reinforced piping, dedicated controls, and trained technicians.
How do you choose between R744 and R134a?
You should consider three factors:
- Your system design requirements
- Local regulations
- Long-term operating cost
In most cases, R744 is the better long-term option.
Why is R744 operating pressure so high?
- Transcritical Cycle
- 31.1°C Critical Temperature
- Gas Cooler vs Condenser
Can R744 replace R134a directly?
No. Because:
- Different working pressure
- Different heat exchangers
- Different pipeline designs
You may also find this related blog post useful:
Types of Refrigerants: The Complete Guide
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