What is a ducting kit and how do I fit one?


A common question people ask is “I’m having a new cooker hood and I’ve been told I need a ducting kit to get the air outside. What is a ducting kit and how do I fit one?”

The ducting kit

Well a ducting/venting kit comprises of a few components, as shown below, and allows you to direct warm air and cooking odours out of your kitchen and send them outside through an external wall.

Cooker hood ducting kit

As you can see from the image above, the square section of the ducting kit with the vents will go on the outside of your home. The piece of conduit then attaches to that the goes through the wall to the inside of the house. The square section that you can see in the middle attaches to the wall inside your home to cover up any unsightly mess that was created whilst creating the hole. The rest of the conduit attaches to the top of the extractor hood with the supplied 125mm circular connector in the ducting kit, that fits onto the end of the conduit.

This is what the top of the average cooker hood looks like where you attach the conduit and connector to.

Top of extractor hood

A ducting kit is pretty universal and whichever one you buy should be able to accommodate the cooker hood that you have purchased. If in doubt, have a look at the extractor first.

How do I get the hole in my wall?

Now, this is the hard bit! Inside your house you probably have plasterboard walls, then some breeze blocks then the outdoor bricks That’s 3 layers of materials that you have to get through!

Having recently created the hole in my kitchen myself, here is how it was done. Unless you have the tools and knowhow, it might pay to get a professional to do this for you.

(1) Checks were made to ensure  that there were no wires or pipes behind the section where we intended on drilling the hole in the wall with a Stud Detector. The last thing you want to do is drill into a water pipe!

(2) A pilot hole was created from inside the house to outside, with a 13mm masonry bit and a powerful drill. Those battery powered drills don’t really cut the mustard here so a mains powered one is best. The recommendations were that a rotary drill with a minimum power drive of 850 watts should be used and capable of speeds up to 3000rpm.

(3) A 127mm diamond core bit (below) was then used to drill a hole on the inside of the house so that it went as far as possible in the breeze blocks but not as far as the outside bricks.

Diamond core drill bit

(4) The 127mm diamond core bit was then used on the outside, with the drill guide in the centre of it, to ensure that the drill bit maintained its positioned and the 2 half holes met in the middle. Can you have half a hole?? hum…

So, this is what the hole looks like at the moment. I would not recommend performing this exercise in Winter!

Extraction hole

As you can see, the hole on the inside is pretty neat but there are bits of chipped plaster on the edge of the whole. You could use some Polyfilla One Fill to tidy things up but with the 17cm plastic covering that attaches to the wall and the 20cm wide chimney that covers the hole, nobody is ever going to see the imperfections behind the extractor.

Well that’s a ducting kit and how it fits into your kitchen!

8 thoughts on “What is a ducting kit and how do I fit one?”
  • Lee says:

    Definitely worth checking the installation instructions for your particular extraction unit. We originally put in 100mm ducting which we later had to replace with 150mm ducting because our extractor (Luxair LA-90-TEL-SS) recommended 150mm, with 125mm being the minimum – anything lower would have voided the warranty. The larger extractors need to push a lot of air at their higher speed settings. 150mm ducting provides much more capacity than 125mm because the cross sectional area is proportional to the square of the radius.

    Basically, check what your chosen extractor recommends and go with that. It’s also worth knowing that you can get rectangular plastic ducting (with rectangular to circular connectors to connect to the extractor and the outlet vent) for running behind stud walls or in ceiling voids if space is tight. We used some it it was very good.

    August 7, 2017 at 7:47 pm
    • Pete says:

      Hi Lee,

      How did you increase the size of the ducting outlet from 100mm to 150mm? We are struggling with this at the moment because our existing cooker hood uses 100mm ducting but all the new cooker hoods we are looking at use 150mm. We assume that using the core drill bit to expand the existing hole would not be a good idea?
      Thanks for your help,

      October 7, 2018 at 11:11 am
      • Diy Kitchens says:

        Hi Pete, you would be best speaking to a tradesperson regarding this to ensure that opening the hole up will not cause any issues and to ensure a neat finish as possible.

        October 8, 2018 at 9:23 am
      • Lee says:

        Hi Pete

        I’d definitely check with a tradesperson as it depends on your specific setup, where the ducting runs etc. I’m not an expert in this, but it would make sense that all your ducting (i.e. from the cooker hood, the ducting run, and the outlet) are all increased to the larger diameter ducting if that’s possible.

        Our ducting ran behind a stud wall where space was limited, so we used rectangular cross section ducting with rectangular to circular converter connections at each end of the run. We got a tradesperson in to do it.

        Let me know if I can help further.


        October 8, 2018 at 11:48 am
  • George says:

    Where do you buy the diamond core bit from?

    August 20, 2015 at 2:09 pm
    • Diy Kitchens says:

      This one was hired locally but do a search on Google and you’ll find plenty of places that sell them.

      August 28, 2015 at 7:26 am
  • Matt says:

    Are the holes all 125mm?

    August 20, 2015 at 1:53 pm
    • Diy Kitchens says:

      125mm seems to be the standard size, but it is worth checking the documentation on the extraction kit before you drill any holes:-)

      August 20, 2015 at 2:47 pm
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