Transparency log

Data status

Last full methodology review: July 25, 2026

Current status: All 12 calculators operational. Official-reference links checked during the review. No live utility-rate feed is used; readers enter their own rates.

Known limitations

• Installed-cost baselines are planning allowances and are not updated from contractor quotes automatically.
• Climate categories are broad screening inputs, not city-specific design temperatures.
• SEER-to-SEER2 comparisons are directional because the test procedures differ.
• Heat-pump COP is user-entered and does not model an hourly temperature bin curve.
• Square-foot sizing tools cannot replace a room-by-room load calculation.

Update policy

When a source or standard changes, we update formulas, labels, explanatory notes, and this log together. Material changes receive a new review date. We do not silently rewrite calculator history to imply that an old result used a newer method.