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]

Stuff that Mid. I would get a £80 extractor and spend the rest on eating out more often...!

Don't think he cares, looking at 30k for the kitchen & worktops. The Gaggenau appliances added another 10k. I did say it was rather expensive, but I got shot down in flames, rather like Dave OCD.

 

[Dave OCD]

Am I bovvered ?

 

[Midwest]

Am I bovvered ?

Sorry Dave, know how it feels now. Upset one of their mods, got told off

 

[johnduffell]

John, I will bow to some of your possibly superior knowledge on this. I agree with Mid though, a bit of 100mm flexi running for 30cm through an external wall is not going to disrupt things much.
Also, I have never noticed a massive difference in noise levels with the ducting reduced in size to 100mm. Domestic kitchen extractors generally are noisy so and so's..

Don't bow to my knowledge, it's more theory than experience, I'm learning a few things here myself I just have a personal preference for quiet extractors so it's my personal crusade!

 

[HappyHippyDad]

I've used a 152mm core drill for 150mm ducting. Was a snug fit, but was fine. There's a reason they make the core sizes they do... the 117mm core drills that you usually get in sets are for soil pipes (110mm) though will serve for a 100mm fan duct, with ample wiggle room. 127mm for 125mm ducting should be fine.

Was that flexible ducting Steve?

 

[Midwest]

Don't worry hhd, 100mm flexible ducting will be just fine

 

[Leesparkykent]

How can drilling from one side be classed as the wrong way of coring the hole? That video shows some DIY numty having a go.I've never had a problem with bricks blowing. I know where I would rather be stood whilst drilling the hole and that's not at the top of a ladder on a gable end with a drill and core bit in the hand.

 

[happysteve]

Was that flexible ducting Steve?

No, rigid.

 

[Pete999]

I bet I know which thread will the the most popular come next week

 

[Pete999]

How can drilling from one side be classed as the wrong way of coring the hole? That video shows some DIY numty having a go.I've never had a problem with bricks blowing. I know where I would rather be stood whilst drilling the hole and that's not at the top of a ladder on a gable end with a drill and core bit in the hand.

Wouldn't to be up a pair of steps using this blighter

 

[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.