Low-GWP refrigerants on the EPA 608 exam: A2L, HFOs, and the 2026 transition

This is the deep dive, not the overview. If you need the full chemistry map first, families, safety classes, blends, and oils, start with the EPA 608 refrigerant types guide and come back. Here we go narrow and deep on one thing: the refrigerants replacing R-410A and why the exam suddenly cares about them.

What does GWP actually measure?

GWP (global warming potential) measures how much heat a gas traps in the atmosphere over 100 years, relative to carbon dioxide. CO2 is the reference, so its GWP is 1 by definition. A refrigerant with a GWP of 2,088 traps 2,088 times more heat than the same weight of CO2 over that century. That is the entire concept, and the exam tests it as a definition question.

Do not confuse GWP with ODP. ODP (ozone depletion potential) measures ozone destruction relative to R-11 at 1.00, and it is about chlorine. GWP is about heat trapping, and even chlorine-free refrigerants like R-410A score high on it. A refrigerant can have zero ODP and a huge GWP, which is exactly the HFC problem the AIM Act targets.

One wrinkle worth knowing before you drill numbers: GWP values shift slightly depending on which IPCC assessment report a table uses. Most US datasheets and EPA SNAP listings use AR4 values, which is why R-410A shows 2,088 in this guide (AR5 lists 1,924). Memorize the AR4 numbers below; they are what US prep material and providers quote.

What counts as low-GWP under the AIM Act?

The working threshold is 700. Under EPA's technology transitions rule, new residential and light commercial AC and heat pump systems manufactured or imported after January 1, 2025 must use a refrigerant with a GWP below 700. R-454B at 466 and R-32 at 675 clear the bar. R-410A at 2,088 does not, which is why its equipment era ended.

The law behind the threshold is the AIM Act (American Innovation and Manufacturing Act of 2020). It phases down HFC production and consumption through an allowance system, stepping down from a 2011-2013 baseline to 15% of baseline by 2036, an 85% total cut. Know the steps: 90% of baseline in 2022-2023, 60% for 2024-2028, 30% for 2029-2033, 20% for 2034-2035, and 15% from 2036 on.

One regulatory distinction earns you a point on Core. The HFC phasedown is codified at 40 CFR Part 84, a separate part from the 40 CFR Part 82 rules that govern your day-to-day recovery, venting, and certification obligations under Section 608. The phasedown restricts production allowances, not field service: recovering, reclaiming, and recharging existing R-410A systems stays legal. The full timeline, including the July 2026 rule that lets pre-2025 R-410A inventory be installed until it runs out, lives in the AIM Act changes guide.

How do HFOs get a GWP under 5?

HFOs (hydrofluoroolefins) are the chemistry story the exam wants in one sentence: an HFO carries a carbon-to-carbon double bond, and that unsaturated bond makes the molecule fall apart fast. R-1234yf breaks down in the lower atmosphere in about 11 days. R-134a, its saturated HFC cousin, hangs around for roughly 14 years. GWP is driven by how long a gas survives, so an 11-day lifetime collapses R-1234yf's GWP to 4 on AR4 tables and under 1 on AR5.

The naming gives HFOs away. Four digits after the R means an unsaturated molecule, so R-1234yf reads as HFO-1234yf the same way R-134a reads as HFC-134a. Decode the number and you have answered the family question before reading the choices.

HFOs show up on the exam two ways. Pure, as R-1234yf, the automotive AC standard since the 2017-2021 model years, running pressures within about 5% of R-134a. And as a blend component: R-454B is 68.9% R-32 plus 31.1% R-1234yf, and that HFO fraction is what drags the blend's GWP down to 466.

Which low-GWP refrigerant replaces which system?

The exam frames the transition as a mapping exercise: legacy refrigerant on one side, successor on the other. Four pairings cover nearly every question.

R-454B (sold as Puron Advance, Opteon XL41, or Solstice 454B) is the pick of most major US residential manufacturers. R-32 dominates mini-splits, runs 3-5% more efficient than R-410A, and is a pure compound rather than a blend, so no glide or fractionation concerns.

The rule that outranks every pairing: no retrofits. An R-410A system cannot be converted to R-454B or R-32, full stop. A2L refrigerants require equipment engineered for them, with leak sensors, airflow logic, and A2L-rated components built in. Any answer choice describing an A1-to-A2L retrofit procedure is wrong before you finish reading it.

What changes when you service an A2L instead of an A1?

A2L means lower toxicity, mildly flammable, with a burning velocity at or below 10 cm/s. The flame is slow and low-energy, nothing like propane, but it exists, and every handling difference on the exam flows from that fact. Your A1 habits are the wrong answers now.

Two details separate a pass from a guess. First, leak detectors are refrigerant-specific: an instrument calibrated for R-410A may not reliably read R-454B, so A2L work requires a detector rated for the refrigerant in the system, sensitive to at least 5 grams per year, and intrinsically safe. Second, ignition control is procedural, not optional: purge with nitrogen before brazing, keep open flames out until the space is verified clear, and let vapor disperse rather than pool, because A2L vapor is heavier than air.

Recovery itself follows the same 40 CFR Part 82 rules you already know. A2L refrigerants are regulated refrigerants, venting is prohibited, and your Section 608 card is the federal credential that covers handling them. The Core study guide covers those recovery and venting rules in full.

Where do natural refrigerants fit?

Naturals are the floor of the GWP table, and the exam uses them to test whether you can separate climate numbers from safety classes. R-744 (CO2) has a GWP of exactly 1 because it is the reference gas. R-290 (propane) and R-600a (isobutane) sit at 3. R-717 (ammonia) scores 0.

Here is the trap: the lowest-GWP refrigerants are not the easiest to handle. CO2 is A1 and non-flammable but runs transcritical supermarket racks at pressures far beyond anything in residential work. Propane and isobutane are A3, highly flammable, and confined to small-charge self-contained cases and household refrigerators. Ammonia is B2L, both toxic and mildly flammable, and stays in industrial plants.

So each natural trades its near-zero GWP for a different burden: pressure, flammability, or toxicity. That trade-off is why A2Ls, and not naturals, won the residential transition. A question that implies "lowest GWP = safest choice" is testing exactly this.

Who decides which refrigerants you're allowed to use?

The SNAP program (Significant New Alternatives Policy) is the gatekeeper, and it predates the AIM Act. SNAP runs under Section 612 of the Clean Air Act, codified at 40 CFR Part 82 Subpart G. Before any substitute refrigerant reaches your gauges, EPA evaluates it on four axes: ODP, GWP, toxicity, and flammability.

Every substitute lands in one of three buckets: acceptable, unacceptable, or acceptable subject to use conditions. That third bucket is where the A2L era lives. Use conditions are enforceable requirements, things like charge limits, required leak sensors, and equipment listing standards, and R-454B and R-32 systems carry them. EPA has kept adding listings as the transition accelerates, including proposed SNAP Rule 27 for residential and light commercial equipment.

For the exam, keep the division of labor straight. SNAP decides which substitutes are legal and under what conditions. The AIM Act decides how much HFC can be produced each year. Section 608 and 40 CFR Part 82 decide how you, the certified tech, must handle all of it in the field.

Low-GWP refrigerants FAQ