New residential heat pumps and AC systems no longer use R-410A. Here's what changed, why it changed, and the one practical thing it means for you as a homeowner: your line set and tools now need to be rated for a mildly flammable refrigerant.
If your current system was installed more than a couple of years ago, it almost certainly runs on R-410A. A system quoted today runs on something else, most commonly R-454B, and that switch wasn't a manufacturer preference, it was a regulatory deadline. The AIM Act phased down high-global-warming-potential refrigerants starting in 2025, and R-410A's GWP is high enough that new equipment manufacturing moved off it.
Global warming potential (GWP) measures how much a given mass of a gas contributes to warming relative to the same mass of CO2 over 100 years. R-410A carries a GWP around 2,088. Its replacements, R-454B chief among them, carry a GWP around 466, a roughly 78% reduction. That's the entire regulatory rationale: less potent refrigerant escaping from a leak or at end-of-life disposal.
Refrigerants are classified by toxicity (A = lower toxicity) and flammability (1 = none, 2L = lower flammability, 3 = higher). R-410A was A1, nonflammable. R-454B is A2L, mildly flammable: it requires a sustained ignition source and a specific concentration to ignite, and it isn't classified as flammable in the everyday sense a can of aerosol is. But "mildly flammable" is still a real change from "not flammable at all," and the safety codes responded accordingly.
None of this changes how the equipment performs for you day to day, the refrigeration cycle is identical in concept to the one already described elsewhere on this site. It changes what's inside the pipes, and what the installer needs to be trained and tooled for.
