EPA's SNAP program lists R-600a as acceptable, subject to use conditions, in new household refrigerators and freezers, where HFC-134a has been unacceptable since Jan 1, 2021; it also meets the 150 GWP limit EPA's Technology Transitions rule has applied to new household refrigerators and stand-alone retail units since Jan 1, 2025.
R-600a pressure-temperature table
Every 5°F shown. ″ Hg = inches of mercury vacuum.
R-600a saturation pressure, psig at sea level
°F
°C
psig
-40
-40.0
21.4″ Hg
-39
-39.4
21.2″ Hg
-38
-38.9
21.0″ Hg
-37
-38.3
20.7″ Hg
-36
-37.8
20.4″ Hg
-35
-37.2
20.2″ Hg
-34
-36.7
19.9″ Hg
-33
-36.1
19.6″ Hg
-32
-35.6
19.3″ Hg
-31
-35.0
19.1″ Hg
-30
-34.4
18.8″ Hg
-29
-33.9
18.5″ Hg
-28
-33.3
18.1″ Hg
-27
-32.8
17.8″ Hg
-26
-32.2
17.5″ Hg
-25
-31.7
17.2″ Hg
-24
-31.1
16.8″ Hg
-23
-30.6
16.5″ Hg
-22
-30.0
16.1″ Hg
-21
-29.4
15.8″ Hg
-20
-28.9
15.4″ Hg
-19
-28.3
15.1″ Hg
-18
-27.8
14.7″ Hg
-17
-27.2
14.3″ Hg
-16
-26.7
13.9″ Hg
-15
-26.1
13.5″ Hg
-14
-25.6
13.1″ Hg
-13
-25.0
12.7″ Hg
-12
-24.4
12.2″ Hg
-11
-23.9
11.8″ Hg
-10
-23.3
11.4″ Hg
-9
-22.8
10.9″ Hg
-8
-22.2
10.4″ Hg
-7
-21.7
10.0″ Hg
-6
-21.1
9.5″ Hg
-5
-20.6
9.0″ Hg
-4
-20.0
8.5″ Hg
-3
-19.4
8.0″ Hg
-2
-18.9
7.5″ Hg
-1
-18.3
7.0″ Hg
0
-17.8
6.4″ Hg
1
-17.2
5.9″ Hg
2
-16.7
5.3″ Hg
3
-16.1
4.8″ Hg
4
-15.6
4.2″ Hg
5
-15.0
3.6″ Hg
6
-14.4
3.0″ Hg
7
-13.9
2.4″ Hg
8
-13.3
1.8″ Hg
9
-12.8
1.2″ Hg
10
-12.2
0.5″ Hg
11
-11.7
0.1
12
-11.1
0.4
13
-10.6
0.7
14
-10.0
1.0
15
-9.4
1.4
16
-8.9
1.7
17
-8.3
2.1
18
-7.8
2.4
19
-7.2
2.8
20
-6.7
3.2
21
-6.1
3.5
22
-5.6
3.9
23
-5.0
4.3
24
-4.4
4.7
25
-3.9
5.1
26
-3.3
5.5
27
-2.8
5.9
28
-2.2
6.3
29
-1.7
6.8
30
-1.1
7.2
31
-0.6
7.6
32
0.0
8.1
33
0.6
8.5
34
1.1
9.0
35
1.7
9.4
36
2.2
9.9
37
2.8
10.4
38
3.3
10.9
39
3.9
11.4
40
4.4
11.9
41
5.0
12.4
42
5.6
12.9
43
6.1
13.4
44
6.7
14.0
45
7.2
14.5
46
7.8
15.0
47
8.3
15.6
48
8.9
16.1
49
9.4
16.7
50
10.0
17.3
51
10.6
17.9
52
11.1
18.5
53
11.7
19.1
54
12.2
19.7
55
12.8
20.3
56
13.3
20.9
57
13.9
21.6
58
14.4
22.2
59
15.0
22.9
60
15.6
23.5
61
16.1
24.2
62
16.7
24.9
63
17.2
25.6
64
17.8
26.3
65
18.3
27.0
66
18.9
27.7
67
19.4
28.4
68
20.0
29.1
69
20.6
29.9
70
21.1
30.6
71
21.7
31.4
72
22.2
32.2
73
22.8
32.9
74
23.3
33.7
75
23.9
34.5
76
24.4
35.3
77
25.0
36.2
78
25.6
37.0
79
26.1
37.8
80
26.7
38.7
81
27.2
39.5
82
27.8
40.4
83
28.3
41.3
84
28.9
42.2
85
29.4
43.1
86
30.0
44.0
87
30.6
44.9
88
31.1
45.9
89
31.7
46.8
90
32.2
47.8
91
32.8
48.7
92
33.3
49.7
93
33.9
50.7
94
34.4
51.7
95
35.0
52.7
96
35.6
53.7
97
36.1
54.8
98
36.7
55.8
99
37.2
56.9
100
37.8
58.0
101
38.3
59.0
102
38.9
60.1
103
39.4
61.2
104
40.0
62.4
105
40.6
63.5
106
41.1
64.6
107
41.7
65.8
108
42.2
66.9
109
42.8
68.1
110
43.3
69.3
111
43.9
70.5
112
44.4
71.7
113
45.0
73.0
114
45.6
74.2
115
46.1
75.5
116
46.7
76.7
117
47.2
78.0
118
47.8
79.3
119
48.3
80.6
120
48.9
82.0
121
49.4
83.3
122
50.0
84.6
123
50.6
86.0
124
51.1
87.4
125
51.7
88.8
126
52.2
90.2
127
52.8
91.6
128
53.3
93.0
129
53.9
94.5
130
54.4
95.9
131
55.0
97.4
132
55.6
98.9
133
56.1
100.4
134
56.7
101.9
135
57.2
103.5
136
57.8
105.0
137
58.3
106.6
138
58.9
108.2
139
59.4
109.8
140
60.0
111.4
141
60.6
113.0
142
61.1
114.6
143
61.7
116.3
144
62.2
118.0
145
62.8
119.6
146
63.3
121.3
147
63.9
123.1
148
64.4
124.8
149
65.0
126.5
150
65.6
128.3
151
66.1
130.1
152
66.7
131.9
153
67.2
133.7
154
67.8
135.5
155
68.3
137.4
156
68.9
139.3
157
69.4
141.1
158
70.0
143.0
159
70.6
144.9
160
71.1
146.9
Saturation pressures computed with CoolProp 8.0.0 (IsoButane) on October 10, 2026, gauge pressure at sea level. Checked against Hudson Technologies published chart at 8 points; largest difference 0.08 psi. How these numbers are made.
What R-600a is and where it is used
R-600a is refrigerant-grade isobutane, a single-component hydrocarbon with an ASHRAE A3 rating: low toxicity, higher flammability. Linde calls it the refrigerant of choice in domestic and small commercial refrigerators. In the US it is listed for new household refrigerators and freezers, small stand-alone commercial units and vending machines.
EPA made R-134a unacceptable in new household refrigerators from Jan 1, 2021, and lists R-600a as acceptable, subject to use conditions, in that end use. Charges are small: Danfoss notes that the safety regulations it cites limit hydrocarbon charges in household and commercial appliances to 150 g (about 5.3 oz) per system. Linde says R-600a requires a compressor built for it and is not for use as a retrofit replacement.
How to read the R-600a chart
Isobutane boils at 10.9°F at atmospheric pressure. That is warmer than a freezer evaporator, so the low side of a household refrigerator runs in a vacuum. Danfoss makes the same point: these evaporators operate below atmospheric pressure. At -10°F the chart reads 11.4 in Hg vacuum, while R-134a at the same temperature is 1.9 psig.
R-600a is a pure fluid, so bubble and dew are the same:
Superheat: at 5 psig suction, saturation is 24.8°F. Use the superheat calculator.
A compound gauge reading inches of mercury on the suction side of a running R-600a refrigerator can be normal. Background: how to read a PT chart.
Typical R-600a pressures in a household refrigerator
As example saturation temperatures, not targets: a freezer evaporator at -10°F reads 11.4 in Hg vacuum, and a condenser at 100°F reads 58.0 psig. Danfoss notes that R-600a has roughly half the volumetric capacity of R-12, so compressors for it need up to twice the swept volume. Household refrigerators are sealed systems, and the manufacturer's diagnostic procedure governs.
Service notes for an A3 refrigerant
Listed equipment only. EPA's use conditions for hydrocarbon refrigerants include UL safety standards, charge size limits and equipment markings. Never put R-600a into a system built for another refrigerant.
Charge by weight. Danfoss reports that R-600a systems are sensitive to charge errors, and undercharging in particular raises energy use. It recommends an electronic scale. Weigh in the nameplate charge.
Ignition control. Danfoss says to ventilate the room well, route the vacuum pump discharge outdoors and keep ignition sources away. EPA recommends recovery equipment designed for flammable refrigerants. Danfoss says to open circuits with a tube cutter, braze only after the refrigerant is removed and both sides are flushed with nitrogen, and braze under flowing nitrogen, or use solderless press-fit connections.
Purity. Danfoss warns that fuel-grade LPG is not pure enough for hermetic systems. Use refrigerant-grade isobutane.
Oil. Compressors usually run mineral oil. Danfoss notes alkylbenzene or POE is also possible.
Venting. EPA exempts some hydrocarbons from the Section 608 venting prohibition only in listed end uses. Check 40 CFR 82.154(a) before releasing any charge.
A3 sits above A2L in flammability. See A2L refrigerants for how the classes compare.