Question re extractor fan exhaust

[ss]

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

[Vortex11]

if you have a 125mm fan just get a 125mm duct kit such as

and all will be fine.

[ss]

Yes that makes sense. thanks

[fred]

I'd connect the two with solid rather than flexible pipe if possible. Flexi ble pipe plays merry hell with the extraction performance.

Many years ago a 'qualified' kitchen fitter ran the cooker extractor fan in to the cavity with the vain hope that the adjacent vent would cope. It didn 't, with the result that all cooking smells were conveyed to my office on t he opposite side of the house. I could never understand why they were only apparent in that room rather than elsewhere.

Whole shebang was replaced with a Miele unit with a 150mm outlet which I to ok care to mate with plastic drainage pipe of the right dimension. All kitc hen smells are now well and truly under control.

[ss]

Thanks Fred I will order the extractor unit and then see best how to connect to the outside either pipe or a kit.