Can you replace R-134a with R-290 in an existing system?

No. EPA's SNAP program accepts R-290 only in new equipment built for it, and Danfoss says converting an R-134a system to R-290 is not recommended because it was never approved for a flammable refrigerant. R-290 also runs far higher pressures and needs a different compressor, metering and charge.

R-290 vs R-134a: Pressures, Charge Size and Retrofit Rules

Pressures side by side

Saturation pressure in psig at sea level. Evaporating rows use the vapor (dew) value, condensing rows the liquid (bubble) value, which is what you compare with suction and liquid-line gauges. The last column is R-290 minus R-134a.

Saturation	R-134a	R-290	Difference
Evaporator (vapor, dew)
-20°F	3.7″ Hg	10.7	+12.5
0°F	6.5	23.7	+17.2 (+266%)
20°F	18.4	41.1	+22.7 (+123%)
30°F	26.1	51.8	+25.7 (+99%)
35°F	30.4	57.7	+27.3 (+90%)
40°F	35.1	63.9	+28.9 (+82%)
45°F	40.1	70.6	+30.5 (+76%)
50°F	45.4	77.6	+32.2 (+71%)
Condenser (liquid, bubble)
80°F	86.7	129.3	+42.7 (+49%)
90°F	104.3	150.5	+46.2 (+44%)
95°F	114.0	161.9	+48.0 (+42%)
100°F	124.2	173.9	+49.8 (+40%)
105°F	135.0	186.5	+51.5 (+38%)
110°F	146.4	199.6	+53.3 (+36%)
115°F	158.4	213.4	+55.0 (+35%)
120°F	171.2	227.9	+56.7 (+33%)
125°F	184.6	242.9	+58.3 (+32%)
130°F	198.7	258.7	+60.0 (+30%)

Properties

Property	R-134a	R-290
Safety class	A1	A3
Type	HFC, single-component refrigerant	HC, single-component refrigerant
Composition (mass %)	Single component	Single component
GWP (AR4)	1,430	n/a
Lubricant	PAG (automotive), POE (stationary)	POE, PAG or PAO (per compressor maker)
Boiling point (14.7 psia)	-14.9°F	-43.8°F
Critical point	213.9°F, 589 psia	206.1°F, 617 psia
Glide at 40°F evaporating	0.0°F	0.0°F
Glide at 100°F condensing	0.0°F	0.0°F
US status	AIM Act HFC; banned in most new equipment types from 2025 (light-duty vehicles from model year 2025), but servicing existing systems remains legal.	Not an ODS or AIM Act regulated HFC; EPA SNAP-acceptable with use conditions in listed self-contained end uses, most recently commercial refrigeration (June 2024).

Component compatibility

Item	R-134a	R-290
Lubricant	POE (stationary); PAG in automotive AC	Per compressor label: POE, PAG, PAO, MO or AB
Charge size	Nameplate	About 40-45% of the HFC charge mass (Danfoss); charge by weight
Compressor	Sized for R-134a	Swept volume close to R-22 (Danfoss)
Section 608 class	Medium pressure	High pressure
Recovery machine	AHRI 740 (App. B3)	Flammable-rated (App. B4, UL 1963 SB)
Venting	Prohibited	Exempt only in listed end uses (40 CFR 82.154(a)(1))
Cylinder	RAL 7044 gray (legacy light blue)	RAL 7044 gray with red band
SNAP status	Existing systems serviced with R-134a	New equipment only, with use conditions

What changes in the field

R-290 runs much higher than R-134a. From the PT data, at 40°F evaporating R-134a reads 35.1 psig and R-290 63.9 psig. At 100°F condensing R-134a is 124.2 psig and R-290 173.9 psig, nearly 50 psi more. Both are single-component refrigerants, so each has one PT column and no glide.

That pressure gap moves R-290 into a different Section 608 class. At 104°F R-134a saturates at 147.4 psia (medium pressure) and R-290 at 198.6 psia (high pressure) under 40 CFR 82.152. Recovery levels for equipment made after Nov 15 1993 follow the class: medium-pressure under 200 lb to 10 in Hg, high-pressure under 200 lb to 0 in Hg. Most of these systems are small appliances (factory-sealed, 5 lb or less), which need 90% recovery with the compressor running, 80% with it off, or 4 in Hg vacuum.

The charge is the other big change. Danfoss puts a hydrocarbon charge at about 40 to 45% of the R-134a charge by mass, since the liquid volume in the system stays about the same. That makes a small error a large percentage, so charge R-290 by weight on a scale and hit the nameplate.

R-290 is A3 (highly flammable). A recovery machine used on it must be certified under Appendix B4 of 40 CFR 82.158 for flammable refrigerants. Venting is allowed only in the end uses listed in 40 CFR 82.154(a)(1), such as household refrigerators, stand-alone retail units and vending machines; everywhere else it must be recovered. See recovery machine compatibility and the flammability classes.

Retrofit or replacement

You cannot convert an R-134a unit to R-290. The reasons:

EPA’s SNAP listings for R-290 in household refrigerators, stand-alone retail and other commercial refrigeration are for new equipment only, subject to use conditions tied to UL 60335-2-24 and UL 60335-2-89 charge limits and markings.
Danfoss states that converting an R-134a system to R-290 “is not recommended, since these systems are not approved for flammable refrigerant use, so electrical safety is not proven.”
The hardware does not match. Danfoss gives R-290 roughly 150% of R-134a’s volumetric capacity at 45°C (113°F) condensing, a compressor swept volume close to R-22, and a capillary flow rate close to R-404A. An R-134a compressor and cap tube are sized for a different refrigerant.

Linde, which sells R-290 as CARE 40, also describes it as not a retrofit refrigerant. A failed R-134a system is repaired with R-134a, or the equipment is replaced with a unit built for R-290. Repairing R-134a equipment is still legal; 40 CFR 84.54 restricts R-134a (GWP 1,430) in new household refrigerators, stand-alone retail units and vending machines from Jan 1 2025, but servicing existing ones is allowed.

When you do work on factory R-290 equipment, Danfoss notes that pencil driers for R-134a can normally be used, with a 3 Å molecular sieve as for R-134a. Ventilate, keep ignition sources away and never braze on a circuit that still holds refrigerant.

Capacity, efficiency and cost

Danfoss’ volumetric capacity figure (about 150% of R-134a) is a property comparison used to size the compressor, not a system rating. Danfoss also notes that at high superheat with good internal heat exchange the theoretical COP of R-290 and R-134a is higher than for R-22. None of the sources here gives a system-level efficiency percentage for R-290 against R-134a, so none is quoted.

GWP drives the change. R-134a is 1,430 on the AR4 basis; R-290 has no AR4 value, EPA SNAP pages list 3 and 40 CFR 84.64 assigns 3.3. R-290 is not a regulated HFC, so the AIM Act phasedown does not touch its supply. For other values see the GWP chart.

Common questions

Is the R-290 pressure chart similar to R-134a?

No. R-290 reads close to R-22, not R-134a: 63.9 psig at 40°F against 68.6 psig for R-22. Use the R-290 chart for any R-290 reading.

Which is better, R-290 or R-134a?

They are not competing choices for the same box. New self-contained commercial and household equipment uses hydrocarbons such as R-290 or R-600a, while existing R-134a equipment stays on R-134a for its life.

R-290 vs R-134a