AC Replacement Glossary

Plain-English explainers for the technical terms, rebates, regulations, and acronyms that show up when you shop for AC Replacement systems and services. Each entry links the underlying source, lists the numbers that matter, and points to related concepts.

AHRI Certified Reference Number (Matched System)
The certificate proving your new outdoor unit and indoor coil were tested together as a rated pair — the single most important thing to verify.
Manual J Load Calculation
The room-by-room heat-gain calculation that determines what size AC your home actually needs — the antidote to guess-by-square-foot sizing.
Manual S Equipment Selection
The ACCA standard that turns a Manual J load into the right specific unit — sized to 95–115% of the cooling load, not the next box on the truck.
R-454B (A2L Refrigerant)
The low-GWP refrigerant your new 2026 system almost certainly ships with — and what the switch away from R-410A means when you replace.
SEER2 (Seasonal Energy Efficiency Ratio 2)
The efficiency score of the new system you're buying — and the federal minimum that decides which units you're even allowed to install.
Variable-Speed & Two-Stage Compressors
Why a replacement system can run at part-load instead of slamming on and off — the comfort-and-efficiency upgrade behind high-SEER2 units.
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