But on two recent 10-ton RTUs rated 15.2 SEER2, I logged about 8.6 EER2 at 95°F/67°F with 1.2 in. w.c. external static and fan power around 0.9 W/cfm. Are others seeing the same drop once code outdoor air per ASHRAE 62.1 and MERV-13 filtration are in play, or should I be pointing the finger at duct design and economizer calibration despite meeting 90.1 efficiency requirements?
I’d bet the 0.9 W/cfm and MERV‑13 are the culprits — AHRI EER assumes about 0.365 W/cfm, so that gap alone can knock a few points before the compressor even breaks a sweat. Quick A/B: set OA to code-min, verify mixed-air sensor/min-position, and trend EER vs external static; if it jumps >1–2 points, it’s duct/econo, not the unit (@mikeH72’s leakage call). What are your clean-filter ΔP and actual cfm?
Building on @rThomas1990, baseline against the OEM expanded data at your ESP and OA, then do a quick A/B: swap to clean MERV‑8s for an hour and trim airflow about 10% to see if EER2 rebounds. I’ve watched 15.2 SEER2 RTUs sink to about 8–9 at 95/67 with those add‑ons, . What cfm/ton and supply temp split did you log?