How to Replace an old Ceiling Exhaust Fan?

Just removed your old ceiling exhaust fan? Read on to find out how to select a replacement…

Step 1 – Remove the old fan

The first step is to measure the diameter of the hole left by the old fan, as this will determine how large your new fan will need to be so it fits snugly into the existing hole. A common mistake is to measure the face/cover size of the old fan instead, trying to find a matching fan in this way is extremely difficult due to the large range of ceiling exhaust fans available today.

Step 2 – Determine the motor power required

You will then need to determine how powerful your new fan needs to be. Calculate the volume of the room by multiplying the length, height and width in metres eg 2m x 3m x 3m = 18 cubic metres (m3). It is recommended that an extraction fan achieve a min of 15 air changes in a bathroom environment, so multiply 18m3 by 15 air changes and you get 270m3/hr. This means that an 18m3 room will require a fan capable of achieving 270 cubic metres per hour or higher if 15 air changes are to be achieved. This figure is a minimum however, and can be easily exceeded or even doubled if it is deemed necessary. Use our exhaust fan calculator to help with this calculation.

Step 3 – Your ceiling space

The type of roof you have and space between the ceiling and roof are also very important. If you have a flat roof or are installing the fan between floors, you will need to measure the vertical space to ensure the body of the new fan will fit. If you have a metal roof (especially flat with minimal clearance) it is strongly advised that you select a fan that can vent moisture and steam to the outside air to avoid the build-up of mould and damage caused by condensation. This is less of a concern if you have a tiled roof as natural ventilation is usually achieved via the gaps in roofs tiles.

Step 4 – Will the fan be ducted?

Delivering steam to the outside air can be achieved in two ways; either buying a fan that can be used in conjunction with a roof cowl, or by traveling the air out via ducting to an external vent. If you decide to duct the steam from your bathroom to an external vent via ducting, be aware that most ceiling mounted side-ducting exhaust fans are not designed to be ducted more than two metres, and doing so will result in a significant loss in fan performance. Given this, if you need to run a duct longer than two metres you might consider an inline fan setup (click here for more details).

This article was written on 13th May 2016 by our in house specialist Michael.