R404A vs R448A: The Solstice N40 Retrofit Path
Updated October 3, 2026
R-448A (Honeywell Solstice N40) is one of two dominant next-generation A1 retrofits for R-404A in medium- and low-temperature commercial refrigeration (the other is R-449A / Chemours Opteon XP40, covered in a separate comparison). N40 cuts GWP by approximately 65% relative to R-404A (1,386 vs 3,922), preserves A1 safety class and POE lubricant compatibility, matches R-404A's pressure envelope closely enough for equipment reuse, and shifts service behavior on one axis: zeotropic ~11°F temperature glide vs R-404A's near-azeotropic behavior. Honeywell's Solstice N40 Technical Data Sheet (Publication 3820, September 2019) is the authoritative datasheet and the source of the PT chart used on the R-448A reference page.
- GWP (100-yr)
- 1,386
- Lubricant
- POE
- Glide @ 0°C
- 11.5°F
PT curves, overlaid
Solid line = bubble, dashed = dew where the refrigerant has significant temperature glide.
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-404A | R-448A | Δ vs R-404A |
|---|---|---|---|
| −20°F | 17 PSIG | 17 PSIG | +1.0% |
| 0°F | 34 PSIG | 34 PSIG | +1.6% |
| 40°F | 87 PSIG | 89 PSIG | +2.8% |
| 70°F | 149 PSIG | 154 PSIG | +2.8% |
| 95°F | 220 PSIG | 227 PSIG | +3.0% |
| 120°F | 312 PSIG | 321 PSIG | +2.8% |
Pressure delta visualization: positive = R-448A runs higher than R-404A; negative = lower. Service equipment pressure rating matters when delta exceeds ±20% on the discharge side. For R-404A (zeotropic blend) bubble pressure is shown; for R-448A same rule applies.
Property differences side by side
- GWP impact: R-404A = 3,922, R-448A = 1,386 (−65% vs R-404A). Switching reduces direct climate impact substantially.
- Lubricant: R-404A: POE; R-448A: POE. Same lubricant family — no oil change needed.
- Glide change: R-404A glide = 0.9°F; R-448A glide = 11.5°F. Service measurement (superheat / subcooling) needs dew/bubble curve awareness for the higher-glide blend.
Properties side by side
| Property | R-404A | R-448A |
|---|---|---|
| Type | HFC blend | HFC/HFO blend |
| ASHRAE class | A1 | A1 |
| Composition | 52.0% R-143a / 44.0% R-125 / 4.0% R-134a | 26.0% R-32 / 26.0% R-125 / 20.0% R-1234yf / 21.0% R-134a / 7.0% R-1234ze(E) |
| GWP (100-yr) | 3,922 | 1,386 |
| ODP | 0 | 0 |
| Lubricant | POE | POE |
| Boiling point @ 1 atm | −46.2°C | −45.9°C |
| Critical point | Blend (locus, not point) | 82.7°C / 654 PSIG |
| Temp glide | 0.92°F | 11.50°F |
| AIM Act affected | Yes | Yes |
Choose R-404A if…
Servicing existing R-404A equipment through remaining service life. Reclaimed R-404A remains legal under EPA Section 608 through the AIM Act phase-down; service supply continues from reclaim streams even as virgin allocation tightens. The economic trade-off is rising R-404A cost against retrofit labor + refrigerant cost. On equipment with 3+ years of remaining service life, running through with reclaimed R-404A is often the cost-optimal path — particularly given R-404A's operational maturity (mature service infrastructure, well-understood equipment behavior, established reclaim market).
Choose R-448A if…
Retrofitting an existing R-404A system when GWP reduction is a driver (AIM Act phase-down compliance, EU F-Gas quota positioning, corporate sustainability commitments), or when reclaimed R-404A supply becomes constrained. Solstice N40 delivers 65% GWP reduction while keeping the R-404A retrofit friction low: same A1 safety class (no equipment recertification), same POE lubricant (no oil change), similar pressure envelope (compressor + expansion device generally reuse), similar cooling capacity per Honeywell's approved-OEM equipment tests. N40 has been qualified by major global equipment and component manufacturers per the Solstice N40 Technical Data Sheet.
When neither is ideal
For new equipment installations at very-low-GWP targets (below 150, the limit in 517/2014 Annex III rows 11 and 13), the A2L blends R-454C or R-455A are the direction — both at 146 GWP, with the A2L safety class requiring IEC 60335-2-89 equipment certification. For transport refrigeration retrofits where compressor discharge temperature at high compression ratios matters more than absolute GWP reduction, R-452A (Opteon XP44 / Solstice L40X) is the class-specific choice. For stationary MT/LT commercial refrigeration where A1 safety is required and 65% GWP reduction is sufficient, R-448A or R-449A are the two dominant options (see the r-448a-vs-r-449a peer comparison).
Retrofit and transition
R-404A → R-448A follows the standard next-generation HFC retrofit procedure. The advantages that make N40 a lower-friction retrofit than the R-22 → HFC family:
Oil. Both refrigerants use polyol ester (POE) lubricant. The R-404A → R-448A retrofit skips the oil change entirely — the existing POE stays in place. Filter-drier replacement is standard for any refrigerant change, but the flush-and-refill sequence that mineral-oil systems require doesn't apply here.
Safety class. Both R-404A and R-448A are ASHRAE 34 class A1 (lower toxicity, non-flammable). No equipment recertification, no ventilation upgrade, no leak-detection retrofit — the safety envelope stays the same. This is the property that separates N40 from the A2L blends (R-454C / R-455A) which would require full IEC 60335-2-89 compliance.
Pressure envelope. R-404A is near-azeotropic (approximately 1°F glide) with 40°F saturation at approximately 87 PSIG bubble / 85 PSIG dew. R-448A at the same temperature is approximately 89 PSIG bubble / 72 PSIG dew — bubble pressures within 2 PSIG, but the ~11°F glide spreads the dew side substantially. Compressor and TXV sizing for R-404A generally accommodate R-448A without replacement; check the equipment OEM's approved-refrigerant list for the specific model.
Glide handling — the one operational change. R-404A is near-azeotropic, so service techs treat single-curve saturation as adequate. R-448A is zeotropic with roughly 11°F glide, so superheat measurement must use the dew curve at the evaporator outlet. Using the bubble curve for SH on R-448A would introduce an error equal to the glide (~11°F) — showing as apparent-undercharge readings and driving techs to over-charge the system. The site's superheat calculator handles the dew-curve selection automatically for zeotropic blends.
Charge amount. The typical retrofit charges R-448A to the same weight as the original R-404A specification, with fine adjustment via subcooling on the liquid line. Verify against the equipment OEM's specific retrofit bulletin — Honeywell publishes per-model retrofit procedures for major commercial refrigeration equipment.
Filter-drier and elastomeric seals. Replace the filter-drier during retrofit (standard practice). Elastomeric seal replacement is not typically required for R-404A → R-448A because both refrigerants have similar swell characteristics on the seals used in HFC systems — this contrasts with the R-22 → HFC family where the different swell profile drives seal replacement as a matter of course.
Discharge temperature and capacity. Honeywell's published data (Solstice N40 Technical Data Sheet) states 5-15% lower energy consumption and increased capacity vs R-404A. Actual field performance depends on system design, operating conditions, and OEM tuning; Honeywell notes major global equipment and component manufacturers have approved N40 for use in R-404A retrofits.
Not recommended for. Same caveat as the broader HFC blend family: not suited for centrifugal compressor systems or chillers with flooded evaporators.
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. One or both refrigerants here are AIM Act-affected. US EPA restricts new residential and light-commercial air conditioners and heat pumps using a refrigerant of GWP 700 or more, effective January 1, 2025 (40 CFR 84.54(a)(1)). Limits for other equipment types differ.
- 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.
Standard transition procedure — R-404A → R-448A
Step-by-step service procedure for transitioning an existing R-404A system to R-448A, derived from the property differences above. Always cross-check equipment OEM service literature for the specific equipment being serviced. The steps below codify EPA Section 608 requirements (recovery, evacuation, documentation) plus refrigerant-specific accommodations for lubricant, safety class, pressure envelope, and glide differences. Skipping any of the regulatory steps (leak check, recovery, evacuation, documentation) creates compliance liability; skipping refrigerant-specific accommodations creates equipment-failure risk.
- Leak-check first. Verify the existing system isn't leaking before recharging. No general federal rule bars adding refrigerant to a leaking system; leak-repair duties apply by appliance size (40 CFR 82.157 for appliances with 50 lb or more of class I/II refrigerant, and 40 CFR 84.106 from January 1, 2026 for appliances with 15 lb or more of HFC refrigerant with GWP above 53).
- Recover R-404A. Use a recovery machine rated for A1 refrigerants. Recover into properly-labeled cylinders; don't mix recovered R-404A with virgin or recovered R-448A (cross-contamination invalidates reclaim).
- Lubricant compatible — no oil change required. Both refrigerants run on POE lubricant family. Keep the existing oil charge; just replace the filter-drier and any compromised seals.
- Replace filter-drier. Install a new drier rated for R-448A (POE lubricant). Filter-driers are single-use after exposure to a refrigerant; the old drier may have absorbed contaminants you don't want carrying into the new charge.
- Pressure-test and evacuate to ≤500 microns. Pressure-test with dry nitrogen to verify no leaks. Pull deep vacuum and hold ≥30 minutes with vacuum pump isolated to confirm no leak-back. This step is non-negotiable — non-condensables (air, moisture) trapped in the system raise discharge pressure and damage the compressor.
- Charge R-448A by weight to nameplate. Use a calibrated recovery / charging scale. Charging by gauge feel produces frequent overcharge errors.
- Verify with SH and SC at steady state. R-448A is zeotropic with 11.5°F glide — use the dew curve at suction for SH, bubble curve at discharge for SC. Wrong-curve selection introduces error equal to the glide. Target SC = 8-12°F for TXV systems; target SH per OEM nameplate.
- Document and label. Update the equipment data plate to reflect R-448A. EPA Section 608 requires records of refrigerant added / recovered; OEM warranty may require documentation of approved-refrigerant substitution.
Lifecycle and operational context
Beyond the per-service-call decision, the R-404A ↔ R-448A 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-404A = 3,922 GWP; R-448A = 1,386 GWP. Switching from R-404A to R-448A reduces direct refrigerant climate impact by 65%.
- AIM Act exposure: Both refrigerants are subject to the AIM Act phase-down (HFC allocation declining toward 15% of baseline by 2036). One or both have a GWP of 700 or more: US EPA restricts new residential and light-commercial AC and heat pumps at that level, effective January 1, 2025 (40 CFR 84.54(a)(1)). Limits for other equipment types differ.
- EU (Regulation (EU) No 517/2014, replaced by (EU) 2024/573): R-404A (GWP 3,922) meets 4 Annex III placing-on-the-market prohibitions; the earliest is Refrigerators and freezers for commercial use (hermetically sealed equipment) (GWP ≥ 2500) from January 1, 2020. R-448A (GWP 1,386) meets 2 Annex III placing-on-the-market prohibitions; the earliest is Refrigerators and freezers for commercial use (hermetically sealed equipment) (GWP ≥ 150) from January 1, 2022.
- Service supply outlook: Service supply of AIM Act-affected refrigerants persists during phase-down via reclaimed and allocated production, with prices rising as supply tightens. Plan for refrigerant cost escalation over equipment lifetime.
- 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-404A → R-448A
What a service technician needs to know when transitioning from R-404A to R-448A (or comparing them for new equipment specification). Two real-world scenarios show how the difference plays out in practice.
Pressure envelope check for R-404A → R-448A
Scenario · Field tech needs to know: do R-404A service tools handle R-448A, or does the pressure delta require new equipment? PT chart comparison at service temperatures gives the answer.
| Temp | R-404A | R-448A | Δ |
|---|---|---|---|
| 40°F | 87 PSIG | 89 PSIG | +2.8% |
| 70°F | 149 PSIG | 154 PSIG | +2.8% |
| 95°F | 220 PSIG | 227 PSIG | +3.0% |
Service-side implications: lubricant and safety
Scenario · Beyond pressure envelope, the switch from R-404A to R-448A affects lubricant, safety class, and operating procedure.
| Concern | R-404A | R-448A | Action |
|---|---|---|---|
| Lubricant | POE | POE | No change |
| Safety class | A1 | A1 | No change |
| Glide | 0.9°F | 11.5°F | Curve awareness |
When to use which tool for this comparison
- R-404A full reference — properties, PT chart, lubricant, retrofit options for R-404A.
- R-448A full reference — properties, PT chart, lubricant, retrofit options for R-448A.
- 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
›Is R-448A a simple swap for R-404A?
Close, but the standard retrofit procedure applies: recover R-404A, replace filter-drier, evacuate to 500 microns, and charge R-448A to nameplate weight. Both use POE oil (no oil change), both are A1 (no safety recertification), and the pressure envelope matches closely enough that compressor and expansion device typically don't need replacement. The one operational change is glide handling — R-448A has ~11°F glide vs R-404A's near-azeotropic behavior, so superheat must be measured using the dew curve at the evaporator outlet.
›How much GWP reduction does R-448A deliver vs R-404A?
Approximately 65% — R-448A at 1386 vs R-404A at 3922. Per the Honeywell Solstice N40 Technical Data Sheet, the reduction is documented as '68% lower than R-404A' using slightly different GWP accounting, with 5-15% lower energy consumption and increased capacity in Honeywell's approved-OEM test conditions.
›Do R-404A and R-448A use the same expansion valve?
Usually yes. The pressure envelope match is close enough that R-404A-rated TXVs typically accommodate R-448A operation without replacement, though the ~11°F glide vs R-404A's near-azeotropic behavior may require minor set-point adjustment. Fixed-orifice systems (piston, capillary tube) can retrofit similarly. Check the equipment OEM's approved-refrigerant list and specific retrofit bulletins.
›What is Solstice N40?
Solstice N40 is Honeywell's trade name for R-448A. Marketed as a next-generation retrofit blend for R-404A/R-507 and other high-GWP HFC blends in low- and medium-temperature commercial refrigeration. The composition per the Solstice N40 Technical Data Sheet is 26/26/21/7/20 mass fractions of R-32/R-125/R-134a/R-1234ze(E)/R-1234yf — a five-component HFC/HFO blend. GWP 1,386, A1 safety class.
›R-448A or R-449A for R-404A retrofit?
Both are dominant A1 choices with similar GWP (1,386 vs 1,396), similar pressure envelopes, similar glide, and shared POE + A1 properties. The decision typically reduces to OEM approval for the specific equipment model, local supply-chain preference (Honeywell vs Chemours), and site-level standardization. See our r-448a-vs-r-449a peer comparison for the direct head-to-head.
›Can R-448A be used in centrifugal chillers?
No — Honeywell's Solstice N40 documentation targets DX (direct expansion) commercial refrigeration; centrifugal compressor systems and chillers with flooded evaporators are outside the approved application range. This constraint is shared across the HFC/HFO blend family.