Exhaust Fan Buying Guide

The intention of this guide is to give a basic understanding on choosing exhaust fans and identify any accessories that might be needed.


The information is general in nature and does not constitute specific advice to any client. Fansonline does not take responsibility for a client's choice of a fan or accessories. If you would like specific advice please contact us with your requirements and situation.

1) Capacity
Manufacturers generally recommend an exhaust fan to have a capacity of 10-15 times the air volume in the room (height x width x length). If a fan is being ducted out, it is usually better to increase the capacity to offset air resistance caused by the duct, bends, grilles, etc. To work out the capacity you require, a good starting point is calculating height x width x length of the room, then multiplying the total by 10 for a standard toilet, 15 for a bathroom, and 20 for a bathroom that produces a lot of steam, this will give you the capacity measured in m3/hr. These calculations are general starting points as each situation is different depending on the room and system used. If you are unsure, please seek professional advice, and/or contact us so we can help you.

2) Wall Mount
Most of the exhaust fans will need a grille / vent for the back of the fan, if installed in a wall.

3) Ducting fans out
If exhausting into the ceiling space (and other areas), it is important to make sure there is somewhere for the exhausted air to go out to the outside. If there is not, then it is suggested you exhaust through the eaves, side or through the roof. You will then need some flexible duct (size to match fan) and a vent (grille) or a cowl kit for the roof.