The fan has not changed. The bathroom floor has. Since the new flooring went down, the mirror stays wet much longer unless the door is left ajar. The gap that used to admit replacement air may have become smaller. Before buying a stronger fan, have that route checked.
Mike notices the new floor before the fan catalogue. The old clearance has almost vanished. "Same fan, different doorway," he says. That does not finish the diagnosis, but it changes the first thing worth checking.
A fan cannot continuously remove room air without air entering to replace it. The Broan-NuTone Canadian FAQ identifies inadequate replacement air as one reason bathroom extraction underperforms. This is a useful explanation for a particular symptom, not proof that every slow-clearing mirror is caused by a door.
What changed at room level?
Think about recent work: a thicker floor, a new door sweep, tighter weatherstripping, a rug across the opening or a changed door. Those are easy details to miss when the noisy equipment overhead attracts all the attention. The fan has been loudly campaigning for a replacement; the quiet obstruction at floor level has said nothing.
Note whether the problem occurs with the door in its normal closed position and improves during ordinary use with it ajar. Do not manufacture a steam test or keep running showers to prove the point. Existing observations are enough to give the installer a sensible comparison.
Also separate moisture clearance from mirror temperature. Very cold glass can still show condensation while the room is being ventilated. Mirror appearance alone is not a flow measurement.
Why the door test does not clear the roof route
A restricted room inlet and a restrictive exhaust duct can coexist. Opening the door may improve one part while a crushed duct, stuck damper or poorly connected terminal continues to limit the whole system.
Mike keeps the duct on the inspection list. Improving the doorway would not excuse a disconnected outlet farther along. The installer should check delivered extraction with the room in its usual operating condition, then investigate the path that constrains it. A tissue held to the grille is a rough indication of suction; it cannot establish whether the intended airflow reaches outdoors.
The fan-route article covers that second half. If water drips from the grille, include its timing in the report, particularly whether it follows cold weather, showers or rain. Do not handle a wet electrical fitting to investigate airflow.
Follow both sides of the fan
Extraction needs an incoming route as well as an outgoing one.
Room entry
Air reaches the bathroom through the designed transfer path.
Fan inlet
The grille and fan collect air at the intended operating setting.
Duct and terminal
Air passes through the connected route to a working outdoor outlet.
Normal-use check
Verify delivered flow with the door in its usual position.
Ask for a designed transfer route, not a guessed saw cut
Bathroom air can reach the extract through a suitable door clearance or another designed transfer path. The correct arrangement depends on the room, fan and building. Do not cut an arbitrary gap based on an online rule of thumb.
The Home Ventilating Institute's guidance includes provision for makeup air, but its general recommendations are not a design for every door. Fire-rated assemblies, separation between occupancies, privacy and sound control can all affect permissible alterations. A qualified installer should identify whether the door is an appropriate place to make a change.
Imagine a single-family ensuite door with new thick flooring, compared with a bathroom beside a shared corridor in a different building arrangement. The same visible gap does not establish that the same alteration is acceptable. Describe the building, not just the door width.
Compare the before and after condition fairly
If an installer changes the transfer route, ask for the fan's measured delivery to be checked with the door closed normally. Keep the model, control setting and result with the invoice. Confirm that the outdoor damper operates and that the connected duct has not been ignored.
For your own follow-up, compare ordinary shower routines under roughly similar conditions. Note whether lingering dampness, odour or condensation improves. If not, report the remaining symptom rather than assuming the newly altered door must be opened further.
A quieter replacement fan may be worth choosing when the existing unit also needs replacement. First establish the airflow requirement and route. More motor capacity is a poor way to compensate for a room that cannot admit enough air, and it may leave you with the same wet mirror accompanied by more noise.
