The lower-global-warming-potential refrigerant replacing R-410A in new residential equipment. It's mildly flammable (A2L class), so it comes with updated handling and equipment standards — one reason new-system installs are certification-sensitive.
Around Baltimore, Annapolis, and the DC metro, cooling decisions revolve around humid Mid-Atlantic summers, correct sizing for row houses and older homes, SEER2 efficiency, and whether a repair or a planned replacement is the smarter long-term spend.