Calculating the area of the room you wish to install the ceiling exhaust fan (Length x Width x Height). Then multiply this number by the number of air changes required (approximately 10 for a standalone toilet and 15 for a shower. This will give you the approximate capacity (or airflow) required to ventilate the room.

Try our easy exhaust fan calculator to find the perfect extraction fan based on your room size and application. The steps required in picking out the correct exhaust fan are:

Determine what variant of exhaust is required and how it will be mounted (eg wall, ceiling, window etc). Calculate the area being exhausted (Length x Width x Height). This will give you a figure in m3 (cubic meters). Multiply this with the number of air-changes required (8 for a subfloor/meeting area, 13-15 for a bathroom or toilet?, 15+ for smoke exhaust). If you like to have long, hot showers or are concerned about steaming up the bathroom then please use a figure of 20 – 30 air changes per hour. Determine whether to duct directly into the roof space, duct out through the roof or through a wall/eave.