Just trying to get a fix on what parts I need.
lets say I buy a 125mm extractor fan.
This will be fitted internally.
Externally I will fit a gravity flap
How critical are the dimensions of the flap unit as I am looking at one
that has an overall size of 190 x 260 mm with the flappy part 150 x 220
so this would be larger than the extractor fan exhaust outlet.
Also do I need to connect the extractor outlet to the flap unit with
ducting tubing the distance being approx 220mm