Who this guide is for
- Homeowners whose bathroom fan no longer clears steam
- People preparing to brief a professional about poor extraction
- Anyone seeing lingering condensation or mould despite a running fan
- Owners wanting a clear performance record before an assessment
Telling weak airflow apart from a dead fan
Note whether the fan runs at all, runs but moves little air, or is noisy. A simple tissue held near the grille shows whether it pulls air, and how strongly, without you opening anything.
Record how long steam takes to clear and whether the mirror stays fogged well after use.
- Fan runs but the mirror stays fogged
- Steam lingers long after a shower
- The fan sounds laboured or rattly
- Little or no pull at the grille
Signs that moisture is not leaving
Record accompanying signs — condensation on walls or the ceiling, peeling paint, mould in corners, a persistent damp smell. These show the consequence of weak extraction.
Note whether the problem is year-round or worse in cold weather.
Where the air should go
Note where the fan vents to — an external wall outlet, a roof terminal, or whether you are unsure. If you can safely see the external outlet, note whether its flap opens and whether it looks blocked.
You are recording observations, not inspecting ducting in the loft or working at height.
Photographing and timing
Photograph the fan grille, any external outlet visible from the ground, and the condensation or mould that results. Time how long steam takes to clear and log it across a few uses.
Avoid removing the cover or poking into the fan, which is an electrical fitting.
- Tissue test at the grille to gauge pull
- Time steam clearance over several uses
- Do not open the fan or its wiring
Briefing a professional
Bring your timing log, the tissue-test observation, the moisture signs, and photos before contacting an electrician or ventilation professional.
Let them assess the fan, ducting and outlet; your record helps them judge whether it is the fan, the duct, or the setup.
Documentation checklist
- 1Note whether the fan runs, runs weakly, or is noisy
- 2Do a tissue test at the grille to gauge how strongly it pulls
- 3Time how long steam takes to clear, over several uses
- 4Record condensation, mould, peeling paint or damp smell
- 5Note where the fan vents and whether the outlet flap opens
- 6Photograph the grille, any visible outlet, and the resulting moisture
- 7Note whether the problem is year-round or weather-linked
- 8Avoid opening the fan or its wiring
Common mistakes to avoid
- Removing the fan cover or poking inside, which involves an electrical fitting
- Cleaning or disconnecting ducting yourself, especially at height
- Assuming the fan is fine because it spins, when airflow may be weak
- Ignoring mould and condensation that show extraction is failing
- Treating it as a fan-only issue when ducting or the outlet may be involved
When to involve a professional
- An electrician or ventilation professional should assess and work on the fan, its wiring, ducting and outlet
- Do not open the fan or touch its wiring; electrical fittings carry shock risk and are for a qualified electrician
- Where lingering moisture has caused mould, an appropriate professional should also assess that
- What is involved varies by installation and location
Frequently asked questions
Questions readers ask about this topic
My fan spins but the mirror still fogs — what does that mean?
A fan that runs but does not clear steam may have weak airflow from the fan, the ducting, or the outlet. A tissue test at the grille and timing how long steam lingers are useful observations to record for a professional.
Can I open the fan to check it?
No — a bathroom fan is an electrical fitting and should only be opened by a qualified electrician. Record the symptoms from outside, including a tissue test and steam-clearance timing, and leave inspection to a professional.
Why is mould forming if my fan runs?
Mould and condensation despite a running fan suggest the moisture is not actually leaving the room. Recording those signs alongside the fan's performance helps a professional see that extraction is the issue.
Could the problem be the ducting rather than the fan?
It can be — ducting or the external outlet can restrict airflow even when the fan works. Note where the fan vents and whether the outlet flap opens, and let a professional trace where the airflow is lost.
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