Extractor Fan Not Clearing Steam: Causes, Checks & Fixes

Do not block required ventilation without understanding its purpose

Background vents, extract systems and combustion-air openings may be essential. Improve comfort by balancing or redirecting airflow rather than sealing vents completely.

MOST LIKELY CAUSES

Start with moisture sources, airflow and temperature

Blocked or restricted duct Lint, debris, crushed ducting or tight bends reduce airflow.

Undersized or ageing fan The fan may not move enough air for the room.

Poor make-up air A tightly sealed room prevents air entering to replace extracted air.

External grille or backdraught flap stuck The discharge route may be obstructed.

◫ Symptom variations Match the humidity, airflow and timing pattern. ⌄

Fan sounds normal but steam remains
Mirror stays wet
Airflow weak at grille
Fan noisy or rattling
Problem worse with door shut

✓ Quick checks Simple checks before replacing equipment. ⌄

Measure humidity with a digital hygrometer.
Check extract fans are moving air outdoors.
Inspect visible grilles, filters and duct routes.
Note whether doors and windows affect airflow.
Check for hidden leaks or persistently damp materials.

Important: A noisy fan is not proof of useful airflow. Check actual extraction at the grille.

1 Step 1 — Check visible airflow Control moisture at source, confirm real airflow and keep surface temperatures stable. ⌄

Use a tissue at the grille and compare with normal operation.

2 Step 2 — Inspect accessible grilles and ducting Control moisture at source, confirm real airflow and keep surface temperatures stable. ⌄

Look for blockage, crushed sections and excessive bends.

3 Step 3 — Check room air supply Control moisture at source, confirm real airflow and keep surface temperatures stable. ⌄

Confirm there is a suitable gap under the door or another air path.

⌁ Why the problem happens How moisture, airflow and temperature interact. ⌄

A fan may run without clearing steam if airflow is weak, the duct is restricted, the external grille is blocked or the room lacks enough replacement air.

⌘ Advanced checks Further diagnosis for persistent humidity or poor airflow. ⌄

Measure airflow where possible.
Check duct length against fan capability.
Inspect external termination and flap.
Review timer or humidistat settings.
Replace with a suitable fan for the duct arrangement.

◇ Tools and information needed Useful items for accurate checks. ⌄

Digital hygrometer
Airflow or tissue test
Fan and duct specifications
Room temperature readings
Inspection for leaks, damp and blocked vents

▣ Parts or improvements that may help Common items linked to this problem. ⌄

Replacement extractor fan
Rigid or insulated ducting
External grille
Backdraught shutter
Timer or humidistat control

! When to call a professional Conditions that should end basic DIY diagnosis. ⌄

Required ventilation or combustion air may be affected.
Fans need electrical or duct alterations.
Humidity stays high despite normal ventilation.
Hidden water ingress or damp is suspected.
Whole-house ventilation needs balancing or redesign.
Mould or condensation is widespread and recurring.

? Frequently asked questions Common ventilation and humidity questions. ⌄

Should vents be closed in winter?

Usually not. Background ventilation helps control moisture. Draughts should be managed with suitable vent design or balancing.

Is 70% humidity too high?

Persistent levels around 70% are high enough to increase condensation and mould risk, especially on cold surfaces.

Will a dehumidifier replace ventilation?

No. It can help control moisture, but it does not provide fresh air or remove pollutants in the same way ventilation does.