I want to replace an old Xpelair window fan (model FXC6) as it's too powerful. See
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believe it's called a "6 inch fan". The blade diameter is 6inches (150mm).The diameter of the circular hole in the window is 184mm (seven and a quarter inches).
Is this hole diameter standardised so that a replacement "6inch/150mm fan" from BLOGGS & CO would be expected to fit a window hole of 184mm diameter?