Minimum Efficiency Reporting Value (1–20) — how well a filter captures particles. MERV 8 handles dust; MERV 11–13 captures allergy-relevant fine particles. Ratings above ~13 need a deep media cabinet, not a standard 1-inch slot, or they choke airflow.
Air-quality terms map to humidity control in muggy Chesapeake summers, filtration (MERV), ventilation for tighter renovated homes, and duct condition in houses that have seen decades of retrofits.