Drilling Through Wall for Cooker Extractor

30 Jun 2005
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United Kingdom
I need to fit an extractor kit to my cooker to vent to outside. The manufacture recommends a 125mm vent kit but also says that a 100mm kit can be used but could not guarantee the performance of the hood. The problem I have is that I can easily borrow from a friend the necessary size core drill bit for the 100mm kit but would this affect the performance of the hood. Or I could purchase/hire the necessary core bit for the 125mm kit. Does any one have any experience of doing this job and noticed a difference in cooker hood performance when downsizing
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A lot depends on the length of your ducting run.....bear in mind smooth ducting is much better than the convoluted flexible stuff to flow air.
If its literally just through the wall then 4” will do - if its longer then Id go for the 5”......it could be easier to obtain the louvre vent too.
John :)
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Thanks for your replies.
Just to recap. For a 100mm extractor vent would you recommend a 127mm core bit. Also, as it will just be going straight through the wall (max 450mm) can I use 100mm soil pipe to put through the hole and connect the vent to?
on any venting or ductin for any extractor or appliance the venting or ducting can increase as it goes to discharge but it shouldn't decrease.
decreasin can cause a possibility of cooling in the vent an particles collecting.
hard wall venting is best in 150mm.

but mfr's instructions rule.
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If you reduce the duct size the volume will decrease and increase velocity so it's not advisable. For a 125dia fan the equiv duct would me 60x200 which you can get in PVC, you can also get 'air bricks' that connect up to that so if it's too much bother to core out the opening, you could replace a brick with one of these louvres.

Attached image is an example.

100mm extractor vent would you recommend a 127mm core bit

You might do it with 105. Duct is measure ID+Wall thickness so I think pvc is usally 2mm so 104 OD. 127 will give you extra wiggle room of course.


  • 3500TE_-_Ducting_to_Airbrick_Adapter_Sets_with_Terracotta_Airbrick.jpg
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Easy to do with long sds drill , short sds bit , hammer and chisel

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