The fan hums faithfully. The mirror stays foggy. Then someone opens the door and the room seems to recover faster. The door may be part of the ventilation system, however little it resembles a mechanical component.
Air leaving the room needs a way to be replaced
Broan-NuTone Canada's fan FAQ identifies insufficient replacement air as a cause of poor extraction. It also notes that cold surfaces can still fog. Do not diagnose performance from the mirror alone or assume one standard door gap suits every installation.
Check the whole route before trimming the door
Ask the contractor to inspect the grille, fan, duct restrictions, damper, and outdoor termination, and assess airflow with normal door positions. Coordinate any door change with its required function, especially in a suite or separation. A higher-capacity fan can leave the same restriction unresolved.
Before the next step
- Notice whether normal door position changes performance.
- Have exhaust and replacement-air paths assessed together.
- Review the door function before cutting or removing components.
Quiet, privacy, and airflow share the same small room. A good detail balances them instead of asking the fan to pull air through a closed argument.