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Discuss Some advice regarding 125mm hole for cooker hood fan please? in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. happyhippydad
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    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    Morning all..

    I am about to quote for a cooker hood installation including core drilling for the vent. The fan is 125mm.

    I have checked upon the sizes of core drill bits and 127mm is the closest fit. I cant see the 125mm ducting getting through that due to the outer diameter of the ducting being greater than 127mm. Does it fit through?

    How much of an impact would it have on the motor if I used a 125mm-100mm reducer for the ducting?

    Could I cut a 152mm hole and use a larger vent on the outside wall, also using a 150mm-125mm reducer for the ducting?

    Cheers.
     
  2. Pete999
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    Doesn't the instructions on the Fan/ducting tell you what size hole is required?
     
  3. Murdoch
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    Murdoch Electrician's Arms

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    Woking
    Have you measured the outside diameter of the ducting? Surely that's 125mm, not the inside!
     
  4. Wilko
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    Wilko Electrician's Arms

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    Last edited: Aug 29, 2017
  5. happyhippydad
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    happyhippydad Member Electrician's Arms

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    Gloucestershire
    I've just measured some rigid 100mm ducting I have Murdoch, the outer diameter is 103-104mm. I'm pretty sure with ducting (unlike conduit) the specified size is for the inner hole, stand to be corrected though? Flexible ducting, although more malleable has an even bigger outer diameter relative to its inner diameter.

    I also remember drilling a 107mm hole for 100mm rigid ducting and it 'just' scrapes through.
     
    Last edited: Aug 29, 2017
  6. happyhippydad
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    happyhippydad Member Electrician's Arms

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    Gloucestershire
    The customer has the instructions Pete but I cant see them being much use in this case as they will just say drill a 125mm or 127mm hole. I'm trying to preempt any problems after scouring the internet and seeing that this is a common problem with 125mm ducting.
     
  7. Midwest
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    Midwest Electrician's Arms

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    Oxfordshire
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  8. HandySparks
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    HandySparks Trusted Advisor

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    Worth a careful measure-up. It's not exactly the same thing, but I've definitely installed a "125mm" room ventilator using a 127mm core drill.
     
  9. egg67
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    egg67 Electrician's Arms

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    Surrey
    Did one not long ago, 125 DIA from fan instructions said drill hole at 130 DIA, all I did was fit a reducer to the cooker hood, add 5mm to ducting size and it will fit
     
  10. happyhippydad
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    happyhippydad Member Electrician's Arms

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    Gloucestershire
    So you used a 125mm-100mm reducer and then drilled a 107mm hole?
     
    Last edited: Aug 29, 2017
  11. egg67
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    egg67 Electrician's Arms

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    Surrey
    No l used a 105 but that was because I had one, 107 will do the job just as good, you just do not want it too Tight on the ducting as it makes it hard to get it in, the cover will hide the hole bit off sand and cerment and rember to drill from both sides not just from one
     
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  12. happyhippydad
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    happyhippydad Member Electrician's Arms

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    Gloucestershire
    This seems like the best option but if the the motor is designed to remove air through a 125mm hole will it not be straining to remove through a 100mm hole?
     
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  13. Pete999
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  14. Pete999
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    Pete999 Trusted Advisor

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    Shouldn't think it will make any difference
     
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  15. egg67
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    egg67 Electrician's Arms

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    Surrey
    No the moter is designed so that it can push air a certain Length from hood Manufacturers allow for bends so all will be fine, if using flexible duct make shore you pull it out straight first and then fit it
     
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  16. Midwest
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    Midwest Electrician's Arms

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    Oxfordshire
    Think the 90' bend in the ducting would have a worse effect.
     
  17. HandySparks
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    HandySparks Trusted Advisor

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    Why?
     
  18. HandySparks
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    HandySparks Trusted Advisor

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    Business Name:
    Neish Electrical Services
    Why?
     
  19. HandySparks
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    HandySparks Trusted Advisor

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    It won't strain the motor (might even reduce the load slightly, depending on the characteristics of the motor) but it will reduce the flow for a given fan speed (as will more duct length or bends). Whether this matters to you or your customer is hard to judge.
     
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  20. Pete999
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    To stop break of the material you are drilling through
     
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  21. valleybilly
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    valleybilly Scuber Do

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    Manchester
    + 2mm addition to core drill sizes is more than enough for fitting flexi ducting . The bigger ducting size also reduces dB when in full power mode so 150mm is even better on a 100mm system.
     
  22. LankyWill
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    LankyWill Electrician's Arms

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    Northants
    127mm is the standard for cookerhood extracts, if your struggling to fit the duct through get a hammer and block of wood and wack it.
     
  23. Pete999
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    Pete999 Trusted Advisor

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    Like the technical talk there Will, "get a hammer and a block of wood and wack it out" nice bit of engineering speak like it.
     
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  24. egg67
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    egg67 Electrician's Arms

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    Surrey
    A lot of MI will say core size 5mm bigger than ducting it allows for movement and gives you a bit of leeway to set the duct so condensation does not flow back to fan.
    Handyspacks as pete999 said saves a lot of making good
     
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  25. Midwest
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    Midwest Electrician's Arms

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    Oxfordshire
    A mate of mine, had to route his ducting through 2 x 45' bends and 3.5m of ducting. Still stops his kitchen steaming up.
     
  26. HandySparks
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    HandySparks Trusted Advisor

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    I've never had any break away of material on the exit side when using a core drill.

    I guess if you have the drill on 'hammer' you would, but that's not how most core drills are used.

    Surely, getting a core drilled hole to meet up accurately when drilled from both ends would be difficult?
     
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  27. Pete999
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    Not really drill through from one side until the pilot shows and then drill through from the other side with the core drill engaged, rocket science is not required.
     
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  28. HandySparks
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    HandySparks Trusted Advisor

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    But why would you bother? I've never had any problems with drilling from one side only with a core drill.
     
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  29. Midwest
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    Midwest Electrician's Arms

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    I've done both ways, ones okay for flexible ducting not for solid. Let the machine do the work, and don't be so impatient :)
     
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  30. Pete999
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    Do what's best for you Mate I'm only explaining the right way of doing it, if your way suits you carry on.
     
  31. Pete999
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  32. egg67
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    egg67 Electrician's Arms

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    Surrey
    Think it's just the way you are shown How to do things , was always told to drill a pilot hole first then the biggy and go at it from both sides, but that was 34 years ago so things change with time, drill bits have got better and making good is just a bit of silicon
     
  33. Pete999
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  34. Pete999
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    Pete999 Trusted Advisor

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    Now you have to agree that's bull shyeet, not the vid your statement it's only a bit of silicone.
     
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  35. egg67
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    egg67 Electrician's Arms

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    Surrey
    Think it's just the way you are shown How to do things , was always told to drill a pilot hole first then the biggy and go at it from both sides, but that was 34 years ago so things change with time, drill bits have got better and making good is just a bit of silicon
     
  36. jackhammerJIM
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    jackhammerJIM Regular EF Member

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    north yorks
    If you do plan on drilling from either side make sure the pilot bit is the exact same size as the sds bit .
     
  37. marc8
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    marc8 Electrician's Arms

    Location:
    Essex
    Business Name:
    MTS Electrical Ltd
    220 x 90 mm is approx 6"
    204 x 60mm is approx 5"
     
  38. marc8
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    marc8 Electrician's Arms

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    Essex
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    MTS Electrical Ltd
    lucky these days from what i have seen drill pilot hole, drill in 1" then club hammer, think it is in case they loose to many diamonds or is it too much time i am not sure maybe my age.
     
  39. egg67
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    egg67 Electrician's Arms

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    Surrey
    Silicon, sillycon or silicone it's all the same at the end of the day, just when I started out was drummed in to me that you do a good job as in Measure twice cut once, drill little them bigger, keep mess to a minimum and leave a good job
     
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  40. NDG Elecs
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    NDG Elecs Electrician's Arms

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    Tyne and Wear
    I think you are overthinking this a bit HHD. Core your ~105mm hole and use a 125-100mm reducer above the fan. It will work fine. :)

    A good tip for hard engineering brick is to core through by around 25mm then stitch drill holes around the circle to speed up the remaining coring.

    I sometimes core from both sides, depending on the finished surfaces inside and out. Does make it much harder to use rigid ducting though doing it that way. I tend to core from the outside to the inside, this due to the dust levels.
     
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  41. HandySparks
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    HandySparks Trusted Advisor

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  42. NDG Elecs
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    NDG Elecs Electrician's Arms

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  43. happyhippydad
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    happyhippydad Member Electrician's Arms

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    I'm guessing drilling all the way from one side is better if using solid ducting?
     
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  44. happyhippydad
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    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    I shall be adding a FCU next to a kitchen socket then chasing perhaps 1.5m (no filling), fitting the cooker hood, core drilling and fitting ducting and outside vent.

    I've estimated 4 hours but am thinking it may be closer to 5? Just trying to work out the quote!
     
  45. NDG Elecs
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    NDG Elecs Electrician's Arms

    Location:
    Tyne and Wear
    Yeah defo. The actual shape of the core drill helps to keep the hole straight. If you core from both sides it is easy to deviate off from a nice straight line. Don't forget to angle it slightly to prevent water any water from coming in from the outside.

    I think four hours sounds about right. 30-90mins on the core itself. 60-90mins chasing, fcu etc. Remainder for testing and tidying up.
     
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