RefrigerantASHRAE R-600a

R600a (Isobutane) PT Chart

Q: What's R-600a's GWP?

1 — essentially zero. The short atmospheric lifetime (weeks-scale, broken down by OH radical attack on the molecule) drives the very low GWP. R-600a sits in the same natural refrigerant low-GWP tier as R-290 (propane, GWP 3.3), R-744 (CO₂, GWP 1).

Updated October 12, 2026

R-600a · Isobutane

A3 Lower toxicity, higher flammabilityHydrocarbon

Illustration of a refrigerant cylinder painted light green gray (RAL 7044), the color AHRI Guideline N-2017 calls for on all new refrigerant containers from 2020^{[7], section 4.8}. Label: R-600a, safety class A3, GWP 1. Red band on the shoulder: AHRI Guideline N-2017 calls for one on containers of flammable refrigerants^{[7], section 4.7}.

C4H10 (isomer)

Isobutane (C₄H₁₀, branched) — natural hydrocarbon refrigerant. A3 highly flammable, GWP 1, zero ODP. Used in new household refrigerators; charge-limited to small systems per safety standards.

R-600a saturation pressure is 11.9 PSIG at 40°F, 30.6 PSIG at 70°F, and 57.9 PSIG at 100°F. These are the gauge readings on a static, fully-saturated system; a running system's high side sits well above them. The full table below runs from −40°F to 150°F in 1°F steps.

Not yet checked against an independent source.

Saturation @ 70°F

30.6 PSIG

GWP (100-yr)

1 US EPA value, 40 CFR 84.64(b)

Boiling point

10.9°F

Sourced facts

ASHRAE safety class: A3^[1]
Chemical formula: (CH₃)₃CH^[1]
GWP (100-yr): 1
ODP: 0^[1]
Normal boiling point: 10.9°F (−11.7°C)^[3]
EPA SNAP approval: 2,011^[5]

R-600a PT calculator Superheat

R-600a PT chart — printable saturation table

Looking for the R-600a PT chart PDF for shop reference? The complete pressure-temperature saturation table is below: every 1° increment from −40°F to 150°F (or to the refrigerant's critical temperature). Use the Print / Save as PDF button in the table header to download a clean, table-only PDF (the rest of the page is hidden from the print output).

R-600a PT Chart — Pressure-Temperature Saturation Table

Computed with CoolProp 7.2.0 in 1°F steps · hvacptcharts.com

R-600a · 1° increments · °F / PSIG

Tinted rows: NBP atmospheric crossover · 32°F H₂O freeze

R-600a pressure-temperature saturation table in Fahrenheit and PSIG
Temp (°F)	Pressure (PSIG)
−40°F	21.4 in. Hg vac.
−39°F	21.2 in. Hg vac.
−38°F	21.0 in. Hg vac.
−37°F	20.7 in. Hg vac.
−36°F	20.4 in. Hg vac.
−35°F	20.2 in. Hg vac.
−34°F	19.9 in. Hg vac.
−33°F	19.6 in. Hg vac.
−32°F	19.3 in. Hg vac.
−31°F	19.1 in. Hg vac.
−30°F	18.8 in. Hg vac.
−29°F	18.5 in. Hg vac.
−28°F	18.1 in. Hg vac.
−27°F	17.8 in. Hg vac.
−26°F	17.5 in. Hg vac.
−25°F	17.2 in. Hg vac.
−24°F	16.8 in. Hg vac.
−23°F	16.5 in. Hg vac.
−22°F	16.2 in. Hg vac.
−21°F	15.8 in. Hg vac.
−20°F	15.4 in. Hg vac.
−19°F	15.1 in. Hg vac.
−18°F	14.7 in. Hg vac.
−17°F	14.3 in. Hg vac.
−16°F	13.9 in. Hg vac.
−15°F	13.5 in. Hg vac.
−14°F	13.1 in. Hg vac.
−13°F	12.7 in. Hg vac.
−12°F	12.2 in. Hg vac.
−11°F	11.8 in. Hg vac.
−10°F	11.4 in. Hg vac.
−9°F	10.9 in. Hg vac.
−8°F	10.4 in. Hg vac.
−7°F	10.0 in. Hg vac.
−6°F	9.5 in. Hg vac.
−5°F	9.0 in. Hg vac.
−4°F	8.5 in. Hg vac.
−3°F	8.0 in. Hg vac.
−2°F	7.5 in. Hg vac.
−1°F	7.0 in. Hg vac.
0°F	6.4 in. Hg vac.
1°F	5.9 in. Hg vac.
2°F	5.3 in. Hg vac.
3°F	4.8 in. Hg vac.
4°F	4.2 in. Hg vac.
5°F	3.6 in. Hg vac.
6°F	3.0 in. Hg vac.
7°F	2.4 in. Hg vac.
8°F	1.8 in. Hg vac.
9°F	1.2 in. Hg vac.
10°F	0.6 in. Hg vac.
11°F NBP (atmospheric)	0.0
12°F	0.4
13°F	0.7
14°F	1.0
15°F	1.4
16°F	1.7
17°F	2.1
18°F	2.4
19°F	2.8
20°F	3.2
21°F	3.5
22°F	3.9
23°F	4.3
24°F	4.7
25°F	5.1
26°F	5.5
27°F	5.9
28°F	6.3
29°F	6.8
30°F	7.2
31°F	7.6
32°F H₂O freeze	8.1
33°F	8.5
34°F	9.0
35°F	9.4
36°F	9.9
37°F	10.4
38°F	10.9
39°F	11.4
40°F	11.9
41°F	12.4
42°F	12.9
43°F	13.4
44°F	14.0
45°F	14.5
46°F	15.0
47°F	15.6
48°F	16.2
49°F	16.7
50°F	17.3
51°F	17.9
52°F	18.5
53°F	19.1
54°F	19.7
55°F	20.3
56°F	20.9
57°F	21.6
58°F	22.2
59°F	22.9
60°F	23.5
61°F	24.2
62°F	24.9
63°F	25.6
64°F	26.3
65°F	27.0
66°F	27.7
67°F	28.4
68°F	29.1
69°F	29.9
70°F	30.6
71°F	31.4
72°F	32.2
73°F	32.9
74°F	33.7
75°F	34.5
76°F	35.3
77°F	36.2
78°F	37.0
79°F	37.8
80°F	38.7
81°F	39.5
82°F	40.4
83°F	41.3
84°F	42.2
85°F	43.1
86°F	44.0
87°F	44.9
88°F	45.9
89°F	46.8
90°F	47.8
91°F	48.7
92°F	49.7
93°F	50.7
94°F	51.7
95°F	52.7
96°F	53.7
97°F	54.8
98°F	55.8
99°F	56.9
100°F	57.9
101°F	59.0
102°F	60.1
103°F	61.2
104°F	62.3
105°F	63.5
106°F	64.6
107°F	65.8
108°F	66.9
109°F	68.1
110°F	69.3
111°F	70.5
112°F	71.7
113°F	73.0
114°F	74.2
115°F	75.5
116°F	76.7
117°F	78.0
118°F	79.3
119°F	80.6
120°F	82.0
121°F	83.3
122°F	84.6
123°F	86.0
124°F	87.4
125°F	88.8
126°F	90.2
127°F	91.6
128°F	93.0
129°F	94.5
130°F	95.9
131°F	97.4
132°F	98.9
133°F	100.4
134°F	101.9
135°F	103.5
136°F	105.0
137°F	106.6
138°F	108.2
139°F	109.8
140°F	111.4
141°F	113.0
142°F	114.6
143°F	116.3
144°F	118.0
145°F	119.6
146°F	121.3
147°F	123.1
148°F	124.8
149°F	126.5
150°F	128.3

R-600a pressure-temperature saturation table in Celsius and kPa
Temp (°C)	Pressure (kPa)
−40°C	−73
−39°C	−71
−38°C	−70
−37°C	−68
−36°C	−66
−35°C	−65
−34°C	−63
−33°C	−61
−32°C	−59
−31°C	−57
−30°C	−55
−29°C	−53
−28°C	−50
−27°C	−48
−26°C	−45
−25°C	−43
−24°C	−40
−23°C	−38
−22°C	−35
−21°C	−32
−20°C	−29
−19°C	−26
−18°C	−23
−17°C	−19
−16°C	−16
−15°C	−12
−14°C	−9
−13°C	−5
−12°C NBP (atmospheric)	−1
−11°C	3
−10°C	7
−9°C	11
−8°C	16
−7°C	20
−6°C	25
−5°C	30
−4°C	35
−3°C	40
−2°C	45
−1°C	50
0°C H₂O freeze	56
1°C	61
2°C	67
3°C	73
4°C	79
5°C	85
6°C	92
7°C	98
8°C	105
9°C	112
10°C	119
11°C	127
12°C	134
13°C	142
14°C	150
15°C	158
16°C	166
17°C	174
18°C	183
19°C	192
20°C	201
21°C	210
22°C	220
23°C	229
24°C	239
25°C	249
26°C	260
27°C	270
28°C	281
29°C	292
30°C	303
31°C	315
32°C	327
33°C	339
34°C	351
35°C	363
36°C	376
37°C	389
38°C	403
39°C	416
40°C	430
41°C	444
42°C	458
43°C	473
44°C	488
45°C	503
46°C	519
47°C	534
48°C	550
49°C	567
50°C	584
51°C	601
52°C	618
53°C	635
54°C	653
55°C	672
56°C	690
57°C	709
58°C	728
59°C	748
60°C	768
61°C	788
62°C	809
63°C	830
64°C	851
65°C	873
66°C	895

CoolProp 7.2.0 · PSIG/kPa = gauge · PSIA = PSIG + 14.6959 · kPa(abs) = kPa(gauge) + 101.325

Full saturation values at 1° increments. Toggle between °F / PSIG and °C / kPa. Use Print / Save as PDF for laminated shop reference, or download the CSV / JSON below for use in other tools. R-600a PT chart data: CoolProp 7.2.0 (published Helmholtz equations of state / mixture models — see the source citations above).

Lower toxicity, higher flammability

Lower toxicity, higher flammability. ASHRAE 34 class 3: lower flammability limit ≤ 0.10 kg/m³ or heat of combustion ≥ 19,000 kJ/kg. Includes hydrocarbons R-290 (propane), R-600a (isobutane), R-1150 (ethylene), R-1270 (propylene).

Flammability: Higher (LFL ≤ 0.10 kg/m³ or HoC ≥ 19,000 kJ/kg)
Toxicity: Lower

Classification per ANSI/ASHRAE Standard 34-2022^{[1], safety group definitions and refrigerant safety classifications}. See full reference.

Saturation pressure-temperature curve

Pressure

Temperature

Highlight at°F

Quick lookup — R-600a

Temp:°F

30.6PSIG(211 kPa)

Range: −40 to 150°F Open full PT calculator →

Common service temperatures

32°F

8PSIG

Freezing

45°F

14PSIG

Heat-pump heat

70°F

31PSIG

Standard

75°F

35PSIG

Test ref

80°F

39PSIG

Warm

95°F

53PSIG

Summer peak

Saturation values from CoolProp 7.2.0^[3]. Operating pressure on a running system differs — see the operating-pressure references for in-use values.

At a glance

Chemistry

C4H10 (isomer)

Isobutane (2-methylpropane)

Lubricant compatibility

MOABPAOPOE

Highly flammable (A3). Mineral oil standard. EPA charge limit 150 g for household refrigerators; updated SNAP rules expanded to small commercial applications.

Common applications

Household refrigerators and freezers (dominant globally)
Wine coolers and small beverage merchandisers
Small commercial refrigeration

Properties

Boiling point (1 atm)
10.9°F (−11.7°C)
Critical point
274.4°F (134.7°C) at 512 PSIG
Molar mass
58.12 g/mol
ODP
0
GWP (100-yr)
1 US EPA value, 40 CFR 84.64(b) IPCC: AR4 not assessed · AR5 not assessed · AR6 not assessed
Atmospheric lifetime
0.02 years
New-equipment status (US)
Not an AIM Act regulated substance; 40 CFR 84.54 GWP limits don't apply.

What is R-600a?

R-600a is isobutane (2-methylpropane, (CH₃)₃CH) — a branched 4-carbon hydrocarbon natural refrigerant^[1]. R-600a is structurally distinct from propane (R-290, straight 3-carbon chain) and offers slightly higher boiling point and different vapor pressure characteristics suited to domestic refrigeration.

R-600a is used in new household refrigerators and freezers as a replacement for HFC R-134a, following EPA SNAP approval in 2011^[5]. The transition is driven by R-600a's very low GWP and zero ODP — meaningful climate impact reduction across the billions of domestic refrigerators in service globally.

Where R-600a is used

Household refrigerators and freezers
Small commercial refrigeration — bottle coolers, beverage display cases
Small ice machines and similar self-contained refrigeration
Limited industrial process refrigeration where R-600a's higher boiling point matters

Regulatory & phase-down status

R-600a faces no phase-down — GWP 1, zero ODP, A3 hydrocarbon outside Montreal Protocol and Kigali Amendment frameworks. The regulatory constraints are equipment-level (charge limits per IEC 60335-2-89) rather than refrigerant-level.

Service notes

R-600a is highly flammable — concentrations between 1.8% and 8.5% by volume in air ignite readily. Equipment design must eliminate all potential ignition sources within the refrigerant circuit: ignition-protected compressor motors, no internal electrical components, brazing only with refrigerant fully recovered and the system inerted^[4].

When R-600a refrigerators are serviced, hydrocarbon-rated equipment and procedures apply: combustible gas detection, no open flames, grounded recovery procedures.

Operating cycle

Phase-down timeline

R-600a is not an AIM Act regulated substance (not one of the 18 HFCs in 42 U.S.C. 7675(c), and not a blend containing one). The 40 CFR 84.54 GWP limits don't apply.

Global warming potential, in context

Household refrigeration

Retrofit and replacement paths

R-600a replaces

Reading the R-600a PT chart

R-600a's PT chart is a single saturation curve (pure refrigerant, no glide).

The operating pressures are very low compared to HFC refrigerants — well within standard 500 PSI manifold gauge ratings. The operational concern is the very-low pressure range rather than high-pressure equipment requirements.

R-600a vs R-12, R-134a: saturation pressure

Saturation pressure (PSIG, gauge) for R-600a vs R-12, R-134a. Each column shows the percent difference from R-600a. Source: CoolProp 7.2.0 dataset.
Temp	R-600a	R-12	R-134a
0°F	6.4 in. Hg vac.	9.1	6.5
40°F	11.9	36.9(+211%)	35.0(+195%)
70°F	30.6	70.1(+129%)	71.1(+132%)
100°F	57.9	116.9(+102%)	124.2(+114%)

Frequently asked

›What is R-600a used for?

Household refrigerators and freezers. R-600a is used as a replacement for HFC R-134a. EPA SNAP approved R-600a for household refrigerator and freezer end-use in 2011^[5].

R-600a is also used in small commercial refrigeration (vending machines, beverage coolers, ice machines) where charge limits per IEC 60335-2-89 allow.

›What's R-600a's GWP?

1 — essentially zero^[2]. The short atmospheric lifetime (weeks-scale, broken down by OH radical attack on the molecule) drives the very low GWP. R-600a sits in the same natural refrigerant low-GWP tier as R-290 (propane, GWP 3.3), R-744 (CO₂, GWP 1).

›Is R-600a the same as butane in a lighter?

Same molecular family (4-carbon hydrocarbons) but different isomer. R-600a is isobutane (2-methylpropane, branched structure); commercial butane fuel is typically a mix of n-butane (R-600, straight chain) and isobutane. Refrigerant-grade R-600a has specific purity requirements (≥99.5% per AHRI 700) and is dried for refrigeration service^[6].

Never use commercial fuel-grade butane as a refrigerant — the impurities and moisture content damage compressor lubrication.

›Is R-600a safe?

The refrigerant is highly flammable (A3 classification). Safety in domestic refrigerator applications comes from extremely small charge sizes — well below the UL 60335-2-24 (2nd ed., incorporated by EPA SNAP, 83 FR 38969) cap of 150 g of flammable refrigerant per refrigerant circuit — and sealed-system construction.

Total refrigerant release from a household R-600a refrigerator into a typical kitchen produces concentrations far below the lower flammability limit (1.8% by volume). The system is designed to be inherently safe through small charge and complete containment.

›What's the difference between R-600a and R-290?

Both are pure hydrocarbon natural refrigerants with A3 classification and GWP near zero. R-600a is isobutane (4-carbon, NBP 10.9°F); R-290 is propane (3-carbon, NBP −43.8°F). R-600a's higher boiling point makes it well-suited to domestic refrigerator operating temperatures; R-290's lower boiling point makes it well-suited to heat pumps and small commercial refrigeration.

›Why did household refrigerators switch from R-134a to R-600a?

Climate impact reduction. R-134a (GWP 1,430) released from end-of-life refrigerators contributes meaningful climate burden across the billions of refrigerators in service globally. R-600a (GWP 1) is essentially zero climate impact. EPA SNAP approved R-600a for household refrigerator end-use in 2011^[5].

›What lubricant does R-600a use?

R-600a is compatible with mineral oil (hydrocarbon refrigerant + hydrocarbon lubricant). POE oil (used with HFCs) is NOT compatible.

›Can I service a household R-600a refrigerator myself?

Generally not advisable. Household refrigerators have small charge sizes that make field service uneconomical compared to whole-appliance replacement. R-600a service requires hydrocarbon-specific procedures (combustible gas detection, no open flames, grounded recovery) that aren't part of typical homeowner skill set.

For commercial-scale R-600a refrigeration (vending machines, beverage coolers), service requires appropriate hydrocarbon-rated equipment and training.

Download this dataset

Full PT chart for R-600a · CC BY 4.0 · attribute the source

CSV JSON

Sources & citations

[1]
ANSI/ASHRAE Standard 34-2022, Designation and Safety Classification of Refrigerants (free read-only version). ASHRAE. 2022. https://www.ashrae.org/technical-resources/standards-and-guidelines/read-only-versions-of-ashrae-standards (accessed October 2, 2026)
[2]
IPCC AR5 WG1 (2013), Chapter 8, Appendix 8.A, Table 8.A.1. IPCC AR5 Working Group I. 2013. https://www.ipcc.ch/report/ar5/wg1/ (accessed October 2, 2026)
[3]
CoolProp 7.2.0. CoolProp (I. H. Bell, J. Wronski, S. Quoilin, V. Lemort). https://coolprop.org/ (accessed October 2, 2026). Bell, I. H.; Wronski, J.; Quoilin, S.; Lemort, V. Pure and Pseudo-pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library CoolProp. Ind. Eng. Chem. Res. 53, 2498–2508 (2014). https://doi.org/10.1021/ie4033999
[4]
UL 60335-2-89 / IEC 60335-2-89 — Safety standard for commercial refrigerating appliances. UL / IEC. https://www.ul.com/services/ul-60335-standards (accessed October 2, 2026)
[5]
EPA SNAP — R-600a acceptable for household refrigerators and freezers. US EPA (SNAP). Approval 2011. https://www.epa.gov/snap (accessed October 2, 2026)
[6]
AHRI Standard 700-2019. 2019. https://www.ahrinet.org/search-standards
[7]
2017 Guideline for Assignment of Refrigerant Container Colors (AHRI Guideline N-2017). AHRI. 2017. https://www.ahrinet.org/system/files/2023-06/AHRI_Guideline_N_2017.pdf (accessed October 2, 2026)