Some advice regarding 125mm hole for cooker hood fan please?

[HappyHippyDad]

Morning all..

I am about to quote for a cooker hood installation including core drilling for the vent. The fan is 125mm.

I have checked upon the sizes of core drill bits and 127mm is the closest fit. I cant see the 125mm ducting getting through that due to the outer diameter of the ducting being greater than 127mm. Does it fit through?

How much of an impact would it have on the motor if I used a 125mm-100mm reducer for the ducting?

Could I cut a 152mm hole and use a larger vent on the outside wall, also using a 150mm-125mm reducer for the ducting?

Cheers.

 

[Midwest]

Personally I would never run flexible ducting through a wall especially the wall of a kit house or cavity wall ! Solid 4" soil pipe is what I use for two reasons (1) with the movement of air in the flexible stuff it can soon rub holes in it causing dampness the only part normally run in flexible normally is from the hood to the roof space (2) if there was a fire the grey soil pipe collapses on its self and helps stop the spread of fire ! The orange soil pipe doesn't have the same caricatureisticts hence why it's gray used above ground and orange below.

I tend to use either manufactures wall kits or with cooker hoods, metal flexible ducting.

Not sure that grey soil pipe has any intumescent properties, by design or accident. Manufactories supply provide fire collars or wraps for that purpose.

Grey soil pipe is generally used above ground as its is uv stabilised, whereas brown is not. It also has slightly different construction, to withstand additional forces, or so Google tells me. But I'm not a plumber