Big difference in extraction between 100mm & 125mm?

[Sprogginz]

Apologies if this thread is better suited to another forum but I thought otherwise. It's not really a question of making the whole but difference in extraction.

I have a kitchen extractor that has a 125mm outlet for extraction. Seems fairly standard size along with a 100mm one.

The problem is that it's very difficult to find a 140mm diamond core bit for the hole in the wall. That's what's recommended by Manrose since the OD of their duct is 137mm. I'm a bit perplexed as I wonder how others do it without drilling a circle of smaller holes.

The diamond core bits seems to jump from 127mm to 152mm! Too small and too big.

So, another option is to convert the 125mm to 100mm instead. There's no problem getting the bits for this.

The question I have, is there is a significant difference between the 2 sizes in terms of volume extraction or rather will I notice the difference?

We have a gas hob with four burners. My wife likes fish so I want to engage in much extraction!

Thanks vey much and hope you can hellp.

 

[rsgaz]

it's very difficult to find a 140mm diamond core bit

142mm is readily available, because it's pretty much 5 5/8 inch in old money. Manrose are just giving their 'minimum recommended' I would guess.

a significant difference between the 2 sizes in terms of volume extraction or rather will I notice the difference?

If it goes directly out the wall, not a lot in it, but it will be louder. If you have a run of ducting before it goes through the wall, definitely go for the 125mm duct all the way.

 

[rsgaz]

Don't forget also, that going from 100mm to 125mm isn't only a 25% increase, because it's cross sectional area we're dealing with, so it's a 56% increase.

The manual for the extractor might say that you'll have no warranty if you use a smaller duct BTW.

 

[Sprogginz]

Thank you all for your replies.

After I posted my thread and did a bit more digging, I eventually found a very good guide. A bit technical for me but got the jist that there's a 'BIG' difference with downsizing! As you mentioned, it could well be noisier with much less extraction.

Thanks for the link too for the 142mm. I've seen a couple myself now but wish I could get one for this weekend! I hope those ones will go through 1950s brick work!

Just seems strange that most sellers jump from 127mm to 152mm. I thought maybe it was because drilling a hole between those sizes might open up an alternative universe or suck me into a black hole and it was a well known fact to the discerning tradesman!