The best option for most bathrooms is a correctly sized exhaust fan ducted directly outdoors. A humidity sensor or run-on timer makes operation more reliable. An openable window can supplement the fan, but natural ventilation is less consistent. Ventilation reduces airborne moisture that encourages mould; it cannot correct leaks, failed waterproofing or existing mould.
Compare the options
| Option | Best use |
|---|---|
| Ducted exhaust fan | The most dependable general option. It actively removes humid air outdoors rather than releasing it into a roof or ceiling cavity. |
| Humidity-sensing fan | Automatically operates when humidity rises, reducing reliance on occupants. It still needs suitable capacity and outdoor ducting. |
| Run-on timer | Keeps the fan operating after bathing. The appropriate duration depends on the room, fan, ductwork and conditions. |
| Openable window or ventilating skylight | Useful as supplementary ventilation or a limited alternative. Its effectiveness depends on weather, opening size and consistent use. |
| Portable dehumidifier | Can reduce indoor humidity when extraction is insufficient, but it does not exchange air or discharge odours and contaminants outdoors. Keep portable electrical equipment away from splash zones and follow its instructions. |
A ducted exhaust fan is generally better than natural ventilation because its performance does not depend as heavily on weather or occupant behaviour.
What affects exhaust fan performance?
Effective extraction depends on the entire airflow path, not just the fan’s advertised capacity.
- Fan selection: Capacity should account for bathroom size and resistance from the ductwork.
- Placement: The fan should capture moisture near the main source where the installation design and electrical safety requirements permit.
- Ducting: Vent the exhaust fan outside. Long runs, sharp bends, restrictions and poor routing reduce airflow.
- Replacement air: Air needs a path into the bathroom, such as a suitable door undercut or designed transfer opening.
- Controls: Use the fan while bathing and afterwards until visible steam and condensation clear. Sensors and timers make this more consistent.
- Noise: A quieter fan is more likely to be used whenever needed.
Do not attempt electrical wiring, roof access or concealed duct installation yourself. Use a licensed electrician for electrical work and a suitably qualified contractor for duct or roof work.
If condensation persists despite effective extraction, stop short of opening walls or attempting concealed repairs. Our Sydney plumbing team can check for plumbing-related moisture sources and help coordinate the appropriate licensed trades.