Thank you for your question. The spigot of the fan which fits within the wall has a diameter of 99mm, however the recommended cut out (hole) through an external wall would be 117mm. This will allow additional space for a wall sleeve/kit and a small slope to outside to ensure any condensation runs out of the property rather than back into the fan.
Answered by: Vent-Axia Product Expert
Date published: 2019-03-10