Ceiling kitchen extractor fan - problem with replacement

[JLC]

Hi i have a problem trying to replace a ceiling kitchen extractor fan in a flat i have just moved into.

I had to disconnect and throw away the old one as it was covered in grease (it was a greenwood airvac i remember) thinking it would be straightforward to get a new one, but I cannot find one that will fit the hole in the ceiling and meet building regs on ventilation rates for kitchens.

The hole in the ceiling is about 140 mm and the outer casing of the old fan was 200mm. The ducting seems to be some type of plastic casing that fills the gap between the ceiling and the floor vents to the outside. 6 inch fans seem to the ones that are powerful enough for the kitchen, but will not fit in the hole and i am not sure about making the hole bigger and fiddling with the ducting myself without knowing what i am doing or having to redecorate afterwards ... so my question is it ok just to connect a smaller fan (5 inches) although it won't be perhaps powerful enough to do the ventilation job it is meant to do in the kitchen?

 

[Taylortwocities]

Whenever I can I replace like for like - that gets around the problems of duct positioning, new wiring etc etc.

If you've got the old fan try and match it here http://www.greenwood.co.uk/PRODUCTS.ASP
or call them and get the equivalent

If not, then you'll have to go into re-engineering. Start off by identifying the size of the duct going out of your ceiling and get something to match.

Dont try and fit a fan in a ceiling unless its designed to do this. Most the more powerful ones are centrifugal fans.

Dont stress yourself about building regs figures..