3 Important factors determine how well an exhaust fan removes steam produced by showers/baths:

1. Extraction Rate

Selecting the right extraction rate of an exhaust fan involves 3 simple steps: Calculate the room size.

Example: Volume of a 2.5m x 2.0m x 2.4m room = 12m³

For reasonably good ventilation an exhaust fan must be capable of replacing the air in a room about 15 times per hour (15 ACH). However a prolonged hot shower on a cold day may warrant more frequent air changes per hour to help get rid of excessive moisture in the air. If required choose a larger ACH value (>20).

Example: Required ACH = 15 x 12 = 180m³/h

Choose an exhaust fan with a higher extraction rate than the required ACH.

Example: Required extraction rate (>180m³/h) = 200m³/h

2. Adequate Cross Ventilation

Getting a decent exhaust fan with a sufficient air extraction rate alone does not guarantee that a room will be well ventilated.

A little planning before the fan installation is carried out goes a long way. To ensure that steam is effectively removed from your bathroom, the exhaust fan should be located, as far as practicable, opposite air intake openings so that cross breeze can traverse through the room.

3. Replenishment Of Exhaust Air

Discharged air must be adequately replenished by fresh air from the outside. Typical sources of air intake are grilles, windows and the openings under doors. If a room has insufficient avenues for air intake, an exhaust fan can become noticeably noisier and cease to extract air effectively. Prolonged use of an exhaust fan inside an airtight bathroom may shorten the useful life of the motor.