Extractor Hood Ducting Run

Discussion in 'Kitchen Fitters' Talk' started by JG1985UK, Aug 30, 2018.

  1. JG1985UK

    JG1985UK New Member


    I'm hoping someone might be able to help me. We are in the process of having an extension built and we are moving our kitchen into a new room. The new room (kitchen/diner) does not have any windows but will have large bi fold doors at the far end to the kitchen and our builder says that he thinks I can get away with a recirculating cooker hood rather than one that takes the air out of the house, which is my preference.

    If we did want to extract the air out of the house we would have to run the ducting in between the ceiling joists, which thankfully run the right way. I have two options, one is a 4.1m straight run to the far external wall (shown in red in the attached picture) and the other is a 3m run which will have a 90 degree bend in it (shown in green).


    Can anyone suggest if one option is better than the other, or are these distances too far for the extraction to be effective.

    If it helps, we are having an induction hob and this is the cooker hood we've ordered --> https://www.neff-home.com/uk/productlist/extractor-hoods/wall-installation/box-chimney/D79MH52N1B

    Any help would be very gratefully received.

  2. kitfit1

    kitfit1 Well-Known Member

    The 3m run with the bend will give you the best extraction. A bend adds another 500mm to the available extraction run, so that option would still be less than a 4.1m straight run by 600mm. With the hood you have chosen, 3.5m effective run is just about at the limit of the hoods capability. To aid extraction even more it would be good to use 150mm solid ducting with a "swept" bend rather than an "elbow" through the wall. Don't allow your builder to use flexipipe from the hood to the wall. Over that distance it will not give a nice smooth air flow and because you are near to the limit for your hood anyway, may well make it ineffective unless you run it full blast all the time.
  3. JG1985UK

    JG1985UK New Member

    Thanks so much Kitfit1, this is just the type of info I was looking for. I was looking at getting something called Megaduct which is solid and rectangular which I guess is better for running between joists, is this something you would recommend?

    Many thanks

  4. kitfit1

    kitfit1 Well-Known Member

    Megaduct is fine, although as far i recall they don't do "swept" bends, only 90 degree bends. If you have the room between the ceiling and floorboards, normal 150mm drainage pipe is cheaper and because it's round is a much easier medium for the air to flow through over the distance you need. Anything that aids air flow is always better and as you will be installing with clear access during the exstension build, it would be a no brainer in my mind. Also a 5inch round vent is easy to get through the wall with a 5inch core drill.
  5. JG1985UK

    JG1985UK New Member

    Perfect! Thanks! I think I’ve just spotted a problem though. If I go with the 3m run with the bend, the ducting is going to have to go through the joist that’s nearest to the external wall in order to get out. I guess that’s not allowed so I’d have to drop the ducting below the joist which would mean some boxing in would be needed in the study but also more bends in the ducting. Do you think this would still be preferable to the 4.1m straight run?

    Sorry for all the questions


  6. kitfit1

    kitfit1 Well-Known Member

    In that case no, because it would need 3 bends i'm guessing ? The 4.1m run would be better, as i said though, use 150mm drainage pipe to give you the best chance of actually shifting air through the hood and then out.
  7. JG1985UK

    JG1985UK New Member

    I will do! Thanks again, this has been really helpful

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