R404A. R134a. R1234yf. R410A.
If you work in HVACR, these strings of letters and numbers roll off the tongue like old friends. But have you ever stopped to ask:
What do they actually mean?
Unlike serial numbers or random model codes, refrigerant designations follow a surprisingly logical system. Once you understand the rules, you can decode a refrigerant’s chemistry, structure, and even safety class—just by reading its name.
Here is your cheat sheet.
🧪 The ASHRAE Standard
Refrigerants are assigned numbers by ASHRAE Standard 34. The system was originally developed by DuPont in the 1950s and later formalised.
Think of it as a chemical barcode compressed into a few digits.
🔢 The Basic Rule: R-XYZ
For most halogenated hydrocarbons (CFCs, HCFCs, HFCs), the number tells you exactly what atoms are inside the molecule.
R-XXX (three digits):
- First digit (rightmost)
= Number of fluorine atoms
- Second digit (middle)
= Number of hydrogen atoms + 1
- Third digit (leftmost)
= Number of carbon atoms - 1 (omit if zero)
Example: R-12
- Carbon: 0+1 = 1 carbon
- Hydrogen: 1-1 = 0 hydrogen
- Fluorine: 2 fluorine
- Remaining bonds filled with chlorine
- Result: CCl₂F₂
Example: R-22
- Carbon: 0+1 = 1 carbon
- Hydrogen: 2-1 = 1 hydrogen
- Fluorine: 2 fluorine
- Remaining: chlorine
- Result: CHClF₂
Example: R-134a
- Carbon: 1+1 = 2 carbons
- Hydrogen: 3-1 = 2 hydrogen
- Fluorine: 4 fluorine
- Remaining bonds? None. Zero chlorine.
- Result: C₂H₂F₄
(tetrafluoroethane)
🔤 The Suffixes Tell the Isomer Story
Why R-134a but R-134 doesn’t exist?
The lowercase letter indicates an isomer—same formula, different atomic arrangement.
- R-134a: 1,1,1,2-Tetrafluoroethane (asymmetric)
- R-134: 1,1,2,2-Tetrafluoroethane (symmetric, less common)
Similarly:
- R-123 vs R-123a
- R-245fa vs R-245ca
If you see a B suffix (R-13B1), that indicates bromine replaces chlorine.
🌪️ Blends: The 400 and 500 Series
Not all refrigerants are single molecules. Many are zeotropic or azeotropic blends
- 400 Series
: Zeotropic blends (temperature glide)
- R-401A, R-404A, R-407C
- The letter indicates different ratios of the same components
- R-404A is not "next to" R-404B; they are formulations, not sequential
- 500 Series
: Azeotropic blends (behave like single fluids)
- R-502, R-507A
- Rare today; most modern blends are 400-series
Note
: The number itself carries no chemical information. R-410A is not chemically related to R-10. The 400/500 series are just catalogue numbers.
🌱 HFOs and The 1200 Series
The newest generation of refrigerants— hydrofluoroolefins (HFOs) —live in the 1000 and 1200 series
- R-1234yf : The poster child for automotive AC
- Tetrafluoropropene (C₃H₂F₄)
- The "1234" echoes the HFC numbering system (4 fluorine, 2 hydrogen, 3 carbon)
- "yf" indicates a specific isomer
- R-1336mzz : Another HFO, used in chillers
These numbers are intentionally designed to map to chemical structure where possible, bridging old logic with new chemistry.
🔥 The Safety Classification
While not part of the number itself, every refrigerant carries a two-part safety code:
Letter 1: Toxicity
- A: Lower toxicity (no identified health risk below 400 ppm)
- B: Higher toxicity
Letter 2: Flammability
- 1: No flame propagation
- 2L: Lower flammability, low burning velocity (new!)
- 2: Flammable
- 3: Highly flammable (hydrocarbons)
Examples:
- R-404A: A1 (non-toxic, non-flammable)
- R-1234yf: A2L (non-toxic, mildly flammable)
- R-290: A3 (non-toxic, highly flammable)
- R-717: B2L (toxic, mildly flammable)
🧠 Why Bother Learning This?
Because the naming convention is a Rosetta Stone
When you see R-32 on a spec sheet, you instantly know:
- It has 2 fluorine atoms, 2 hydrogen atoms, 1 carbon
- It is CH₂F₂
- It is an HFC
- GWP ~675, mildly flammable (A2L)
You don’t need to memorise thousands of refrigerants. You just need to read the number
📝 The Short Version
Refrigerant nomenclature is not bureaucratic noise. It is a chemical fingerprint disguised as a product code.
Next time you see R-438A on a cylinder, you won’t just see a random string. You’ll see a story: a zeotropic blend of HFCs and HCs, designed to retrofit old R-22 systems, carrying an A1 safety rating, and sitting squarely in the twilight of the HFC era.
The number tells you what it is.
The context tells you why it matters.