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

[Dave OCD]

That's HHD doing his cooker hood hole, bit of play to get the ducting through, just to be on the safe side.

 

[mydigitalhome]

Dont reduce the size of duct as it will reduce performance of fan and ability of cooker hood to perform. Use solid steel duct rather than flexi plastic out of choice for a better install or solid plastic duct. Plus suggest on penetrations fill the gap arround with intumescent foam rather than standard builders foam. It is assumed that this on a outside facing wall rather than running through the ceiling void. Remember flexi-duct pipe only works well if it is pulled taught when it is left loose the air movement is reduced and becomes a greater risk of fire due to grease being caught plus from memory the BS indicates that flex tube is max of 1.5m long from fan without compromising install.

 

[mydigitalhome]

Double checked my notes Building & Engineering Services Association - Specification for flexible ducts p.113 Section 30.1 DW/144 advises you not to go over 1.5m hope it helps.

 

[Midwest]

That pretty much rules out using flexible with any domestic bathroom fan, but that's what must are installed. IMO follow manufactures advice and keep it under 3m and you'll have no issues.

 

[vjsmarwick]

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.

 

[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