R290 vs R600a: Propane and Isobutane in HVAC Service
Updated October 3, 2026
R-290 (propane) and R-600a (isobutane) are both natural hydrocarbon refrigerants with essentially zero GWP and no ODP, but they sit at opposite ends of the operating envelope. R-290 saturation at 40°F is 63.9 PSIG; R-600a at the same temperature is 11.9 PSIG — a 5.4× ratio that reflects propane's much higher vapor pressure. Both are ASHRAE class A3 (higher flammability), so equipment and handling are governed by A3 charge-limit standards specific to each application (IEC 60335-2-89 for commercial refrigeration, 60335-2-40 for heat pumps, 60335-2-24 for household refrigerators), but they serve different applications: R-290 in commercial refrigeration and heat pumps, R-600a in small domestic appliances.
- GWP (100-yr)
- 3.3
- Lubricant
- MO, AB, PAO
- Glide @ 0°C
- 0.0°F
- GWP (100-yr)
- 1
- Lubricant
- MO, AB, PAO
- Glide @ 0°C
- 0.0°F
PT curves, overlaid
Both refrigerants are pure or near-azeotropic — single curve per series.
Pressure comparison at service temperatures
Side-by-side pressure values at common service temperatures, computed from CoolProp 7.2.0. Useful for retrofit feasibility — pressure deltas within ±20% typically allow retrofit-compatible service equipment; larger deltas require component pressure-rating review.
| Temperature | R-290 | R-600a | Δ vs R-290 |
|---|---|---|---|
| −20°F | 11 PSIG | −8 PSIG | — |
| 0°F | 24 PSIG | −3 PSIG | — |
| 40°F | 64 PSIG | 12 PSIG | −81.4% |
| 70°F | 110 PSIG | 31 PSIG | −72.2% |
| 95°F | 162 PSIG | 53 PSIG | −67.4% |
| 120°F | 228 PSIG | 82 PSIG | −64.0% |
Pressure delta visualization: positive = R-600a runs higher than R-290; negative = lower. Service equipment pressure rating matters when delta exceeds ±20% on the discharge side. For R-290 (zeotropic blend) bubble pressure is shown; for R-600a same rule applies.
Property differences side by side
- GWP impact: R-290 = 3.3, R-600a = 1 (−70% vs R-290). Switching reduces direct climate impact substantially.
- Lubricant: R-290: MO/AB/PAO; R-600a: MO/AB/PAO. Lubricant systems differ; check compatibility per manufacturer.
Properties side by side
| Property | R-290 | R-600a |
|---|---|---|
| Type | Hydrocarbon | Hydrocarbon |
| ASHRAE class | A3 | A3 |
| Composition | Pure | Pure |
| GWP (100-yr) | 3.3 | 1 |
| ODP | 0 | 0 |
| Lubricant | MO, AB, PAO | MO, AB, PAO |
| Boiling point @ 1 atm | −42.1°C | −11.8°C |
| Critical point | 96.7°C / 602 PSIG | 134.7°C / 512 PSIG |
| Temp glide | 0.00°F | 0.00°F |
| AIM Act affected | No | No |
Choose R-290 if…
Commercial refrigeration (self-contained cases, walk-in coolers, standalone units with hermetic circuits), heat pumps in R-290-designed equipment, industrial refrigeration in propane-rated circuits. R-290 has pressures similar to R-22 (~90–95% at typical operating conditions) which historically made it a retrofit candidate for R-22 systems, though A1 → A3 safety-class flip generally rules that out in practice. Charge limits for self-contained commercial refrigeration equipment (IEC 60335-2-89) depend on the refrigerant's LFL and the equipment design.
Choose R-600a if…
Small hermetic domestic refrigeration (household refrigerators, freezers, wine coolers, small commercial reach-ins). R-600a is the dominant refrigerant in domestic refrigerators globally — Europe adopted it in the 1990s and it now covers most of the world's new domestic refrigerator production. Very low pressures suit small-capacity single-evaporator systems with capillary-tube metering. UL 60335-2-24 (2nd ed., incorporated by EPA SNAP, 83 FR 38969) caps flammable refrigerant at 150 g per refrigerant circuit.
When neither is ideal
For applications requiring A1 non-flammable operation, or charges above the A3 charge-limit thresholds (which depend on the refrigerant's LFL and the room size/volume), an A2L HFC/HFO blend (R-454C for LT commercial refrigeration, R-455A for MT, R-513A for chillers) or a natural refrigerant with different safety profile (R-744 CO₂ for supermarket refrigeration, R-717 ammonia for industrial refrigeration) is the appropriate path. Neither R-290 nor R-600a is suitable for applications requiring large-charge circuits in occupied spaces without engineered ventilation, gas detection, and A3-rated equipment.
Retrofit and transition
R-290 and R-600a are not retrofit candidates for each other. The pressure gap alone — R-290 running roughly 5× R-600a saturation pressure at typical service temperatures — is enough that component pressure ratings, compressor displacement, and expansion-device sizing don't overlap. Both are also matched to distinct application classes at the equipment-design level, not just refrigerant selection.
R-290 systems use hermetic reciprocating or scroll compressors sized for propane's higher volumetric capacity; R-600a systems use much smaller hermetic reciprocating compressors sized for isobutane's low-pressure, low-capacity operating point. Component swap in either direction produces immediate failure or non-operation, not a graceful degradation.
Both refrigerants are miscible with mineral oil (MO), alkylbenzene (AB), and polyalphaolefin (PAO) synthetic oils. That's a shared property, but not enough to bridge the pressure and displacement mismatch.
When a system is being converted between application classes — say, a small commercial cooler being redesigned from a domestic-refrigerator platform — a full equipment redesign is required, not a refrigerant swap. In that redesign, R-290 is the typical choice for commercial applications above the R-600a charge limit.
Regulatory and transition context
Both refrigerants sit in an active regulatory transition driven by climate-impact rules. The transitions affect availability, pricing, and new-equipment specification.
- AIM Act (40 CFR Part 84): US HFC production / import phase-down. Cap declines from 90% allocation (2022) to 15% by 2036. Neither refrigerant is directly affected.
- EU: Regulation (EU) No 517/2014, replaced by (EU) 2024/573 (applying from March 11, 2024); 2024/573 uses AR4 GWPs for HFCs and AR6 for other fluorinated gases (recital 8).
- Kigali Amendment to Montreal Protocol (2016): international HFC phase-down framework. The Montreal Protocol has 198 parties; 174 have ratified the Kigali Amendment (as of August 10, 2026). The AIM Act and EU F-Gas are regional implementations. Schedules differ by country group.
- ASHRAE 34-2022: safety classification (A1, A2L, A3, B1, B2L). For A2L refrigerants like R-32, R-454B, R-454C, R-455A: equipment must be A2L-certified, charge limits per IEC 60335-2-40 apply.
Why R-290 → R-600a isn't a direct retrofit
R-290 → R-600a is a full equipment-replacement decision, not a service-time swap. The barriers below are structural — equipment certification, oil chemistry, pressure ratings — so no field checklist can bridge them. The realistic path is to continue servicing existing R-290 equipment through its useful life, then install new R-600a-rated equipment at end-of-life.
- Saturation pressure delta −67% at 95°F. Compressor, TXV, condenser, and service-valve ratings are engineered around R-290's envelope (162 PSIG at 95°F); running R-600a (53 PSIG) at this delta exceeds the design margins on multiple components. Retrofitting means re-rating hardware, not just changing charge.
Lifecycle and operational context
Beyond the per-service-call decision, the R-290 ↔ R-600a choice sits inside a broader regulatory and lifecycle context. The transition direction (which is the predecessor, which is the successor) is driven by climate policy and the AIM Act phase-down, not technical preference alone.
- GWP profile: R-290 = 3.3 GWP; R-600a = 1 GWP. Switching from R-290 to R-600a reduces direct refrigerant climate impact by 70%.
- AIM Act exposure: Neither refrigerant is directly affected by the AIM Act phase-down. Other regional regulations (EU F-Gas, Kigali signatory implementations) may still apply.
- Service supply outlook: Neither refrigerant faces near-term supply constraints from AIM Act phase-down. Pricing follows normal commodity dynamics.
- TEWI / LCCP framing: Total Equivalent Warming Impact accounts for both direct refrigerant emissions (leakage, end-of-life) and indirect emissions from equipment energy consumption. For HVAC equipment with ≤5% annual leak rate, indirect emissions typically dominate TEWI by 80-90% — meaning equipment efficiency matters more than refrigerant GWP for total climate impact. For commercial refrigeration with higher leak rates, the balance can tip toward favoring low-GWP refrigerants.
Regulatory sources: AIM Act (40 CFR Part 84), EU F-Gas Regulation 517/2014 and update 2024/573, Kigali Amendment to the Montreal Protocol (2016). GWP values on the US EPA basis (40 CFR 84 / IPCC AR4).
Service implications — R-290 → R-600a
What a service technician needs to know when transitioning from R-290 to R-600a (or comparing them for new equipment specification). Two real-world scenarios show how the difference plays out in practice.
Pressure envelope check for R-290 → R-600a
Scenario · Field tech needs to know: do R-290 service tools handle R-600a, or does the pressure delta require new equipment? PT chart comparison at service temperatures gives the answer.
| Temp | R-290 | R-600a | Δ |
|---|---|---|---|
| 40°F | 64 PSIG | 12 PSIG | −81.4% |
| 70°F | 110 PSIG | 31 PSIG | −72.2% |
| 95°F | 162 PSIG | 53 PSIG | −67.4% |
Service-side implications: lubricant and safety
Scenario · Beyond pressure envelope, the switch from R-290 to R-600a affects lubricant, safety class, and operating procedure.
| Concern | R-290 | R-600a | Action |
|---|---|---|---|
| Lubricant | MO/AB/PAO | MO/AB/PAO | No change |
| Safety class | A3 | A3 | No change |
| Glide | 0.0°F | 0.0°F | Minor |
When to use which tool for this comparison
- R-290 full reference — properties, PT chart, lubricant, retrofit options for R-290.
- R-600a full reference — properties, PT chart, lubricant, retrofit options for R-600a.
- PT Comparison Tool — overlay any 2-4 refrigerants' PT curves interactively.
- Retrofit Compatibility Calculator — five-criterion compatibility analysis with verdict.
- Refrigerant Comparison Guide — long-form sourced reference for all common HVAC refrigerant comparisons.
Frequently asked
›Are R-290 and R-600a interchangeable?
No. The pressures differ by roughly 5× at typical operating temperatures — R-290 at 40°F saturation is 63.9 PSIG, R-600a at the same temp is 11.9 PSIG. That means completely different compressor displacement, component pressure ratings, and expansion-device sizing. Equipment designed for one refrigerant cannot operate on the other.
›Are R-290 and R-600a safe for domestic use?
Both are ASHRAE class A3 (higher flammability, lower toxicity). Domestic and small commercial equipment using these refrigerants must comply with charge-limit standards: IEC 60335-2-24 for household refrigerators, IEC 60335-2-89 for commercial refrigerating appliances, and IEC 60335-2-40 for air conditioners and heat pumps. Within charge limits and with properly-designed hermetic equipment, both refrigerants are used safely in millions of installations globally.
›Why is R-600a used in home refrigerators instead of R-290?
Two reasons: R-600a's lower pressure suits the small hermetic compressors used in domestic refrigerators (typical evaporator temperatures of −20 to 5°F correspond to R-600a suction pressures of roughly 0 to 7 PSIG). And R-600a's charge limit under IEC 60335-2-24 aligns well with the charge sizes used in domestic units. R-290 would work thermodynamically but the higher pressure requires larger, more expensive compressors and heavier tubing, and the applications where R-290's capacity is useful (commercial reach-ins, walk-ins) tolerate its higher A3 charge limit under IEC 60335-2-89.
›Can R-290 replace R-22 in older residential AC systems?
Not as a service retrofit. R-290 has been used experimentally as an R-22 pressure match (the two refrigerants have similar saturation curves across the residential AC operating envelope), but the A1 → A3 safety-class flip requires equipment recertification (hermetic sealing, charge limits, ignition-source elimination) that a field retrofit can't achieve on equipment designed for A1 service. New-equipment R-290 residential AC does exist in some markets (particularly for heat pumps) but is engineered from the ground up for A3 operation.
›What are typical R-290 and R-600a charge sizes?
R-290 in commercial refrigeration: modest charges for self-contained cases, scaling up in engineered systems with A3-rated equipment and gas detection. R-600a in domestic refrigerators: small charges, bounded by the IEC 60335-2-24 maximum for household equipment. Both are much smaller than HFC systems of comparable capacity because hydrocarbons have higher latent heat per unit mass.
›What lubricants do R-290 and R-600a use?
Both are miscible with mineral oil (MO), alkylbenzene (AB), and polyalphaolefin (PAO). Most equipment ships with MO or AB. Neither refrigerant requires the polyol ester (POE) oils that HFC systems use, which is an operational simplification for equipment manufacturers and service technicians.