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.
| What you notice | What it may point to | Useful next check |
|---|---|---|
| Extraction improves with the door open | Restricted replacement air | Compare the normal door position with the door open and report the difference |
| Poor extraction with the door open or closed | A restriction or performance problem elsewhere in the exhaust route | Have the grille, fan, duct, damper and outdoor outlet checked |
| Fog mainly on very cold glass | Surface temperature can contribute even with ventilation running | Record room conditions rather than treating mirror fog as an airflow measurement |
| The change followed a new sweep, door or flooring | The alteration may have reduced the air path | Show the assessor what changed before cutting the door |
These are clues to bring to the ventilation contractor, not measurements of delivered airflow. Compare ordinary use with the same fan setting; a quieter motor or a clearing mirror cannot tell you how much air reaches the outdoor outlet. The aim is a bathroom that works with the door where you normally keep it.
If the fan itself drips, use the separate winter bathroom-fan condensation checks. Water in a cold duct and restricted air beneath a door can need different repairs.
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.
Have the airflow checked with the door where you normally keep it. The bathroom needs to work during your actual shower routine, not only during a demonstration with the door wide open.