How to Replace a Wall Exhaust Fan

Once the old fan has been removed and you have noted the size of the existing hole, you will then need to record the dimensions of the room the fan was installed in (LxHxW). This will give you the volume of the room and from there you simply multiply this figure by the number of air changes that need to be met, and this will give you the required extraction rate the fan needs to meet or exceed (we usually recommend 15 air changes per hour as a min base rate).

You will then need to take into account the characteristics of the wall, ie the depth of the cavity inside the wall, and the distance to the outer wall if double brick. If the wall cavity is thin the fan may be too deep to fit between the plaster and external wall, and if the wall cavity is too wide you may need ducting to bridge the gap between the fan and the external wall.

The depth of the wall is also important when selecting an external vent. Many wall fans do not come with a vent for the outside wall, so you may need to choose an external vent to protect it from the elements and cover the outer hole in the wall.

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This article was written on 27th May 2016 by our in house specialist Michael.