hob extrator hole. 100mm or 125mm?

seatbeltnoob

Hi

I wanted to fit a 125mm hob extractor hole. My builder does not have a 125mm core and said they can either do a 100mm hoole and enlargen it to fit 125mm. Or suggest that I cange to 100mm tubing.

I'm worried that 100mm is too small for the extractor and it might strain the motor and cause it to fail. OTOH 100mm would cause less draught in winter.

Whhat do you reckon? Should I go 100mm or 125mm?

EssexExile

125mm, the more airflow the better. You won't get a draught, they have technology to stop that (a plastic flap).

stator

Go to screwfix and buy a 127mm core drill bit (£40). Builder gets to use it once, you keep the bit and sell it on gumtree.

http://www.screwfix.com/p/erbauer-diamond-core-drill-bit-127mm-x-150mm/99629

seatbeltnoob

went wkith 125mm, glad I did, important to bear in mind that the tube connectors take up a big part of the interior cross section of the ducting.

cyclonebri1

seatbeltnoob wrote: »

Hi

I wanted to fit a 125mm hob extractor hole. My builder does not have a 125mm core and said they can either do a 100mm hoole and enlargen it to fit 125mm. Or suggest that I cange to 100mm tubing.

I'm worried that 100mm is too small for the extractor and it might strain the motor and cause it to fail. OTOH 100mm would cause less draught in winter.

Whhat do you reckon? Should I go 100mm or 125mm?

Tell your builder you made it clear you "needed" a 125mm extractor

He quoted for that didn't he:A:A

Don't move from what you want, I think you are bang on right:T:T

stator

seatbeltnoob wrote: »

went wkith 125mm, glad I did, important to bear in mind that the tube connectors take up a big part of the interior cross section of the ducting.

What deal did you make with the builder?

Mr.Generous

The vast majority of houses I work in do not have any extraction, 100mm is such a massive improvement on nowt. I also don't have a 125 core bit so its 100 all the way. if someone wanted a 125 really badly I'd charge £30 more and buy a core bit I suppose.

Fat_Walt

Mr.Generous wrote: »

The vast majority of houses I work in do not have any extraction, 100mm is such a massive improvement on nowt. I also don't have a 125 core bit so its 100 all the way. if someone wanted a 125 really badly I'd charge £30 more and buy a core bit I suppose.

It's not really a case of wanting the hole but why would you use a 100mm hike when the manufacturer specifies a 125mm or 150mm?

ic

100mm = 78.54 cm2
125mm = 122.72 cm2
150mm = 176.71 cm2

The jump in diameter doesn't sound much, but as you can see its a 56% jump in capacity from 100 to 125, and 44% jump again to 150mm. Well worth it, and provides a better throughput from the extractor. Of course, the bigger the hole, the harder it is to drill. (Depending on the wall, I did 125mm diameter in Victorian solid brick wall a few inches from the ceiling. Nearly killed me, I was exhausted from holding the drill up high for a couple of hours as little by little it progressed through the wall!)

seatbeltnoob

the opening on my extractor is 150mm and the exractor came with its own reducing ring to 125mm I'm guessing the manufacturer is perfectly happy with 125mm duct.

My brother got the rectangle boxe and with several right angle bends on the pipwork following the corners. The rectangles offer far less capacity (110 x 54mm) so 59.4cm2.

Plus the right angle bends cause a lot of resistance the ducting should be as straight as possible with as few bends. The other limitation is the length of the ducting. It should be as short as possible.

Luckily for is there is just 1 bend in the pipe and the total lenngth of the pipe is probably 1.2m to the outside wall.