Guides

Plain explanations of the ratings, the test conditions behind them, and what they cannot tell you.

• Ratings explained, October 17, 2026

  SEER2 vs HSPF2: Which Rating Actually Matters?

  SEER2 vs HSPF2: one rates cooling, one rates heating, and across 92 certified systems they barely track each other. What each measures and which to use.