Venting extractor hood through roof

Discussion in 'Kitchen Fitters' Talk' started by SBobs, Jan 5, 2023.

  1. SBobs

    SBobs New Member

    Hi

    I’ve just had a new kitchen and my hob is on an internal wall of a bungalow, and we had planned to vent it through the roof. The kitchen installer has never vented through a roof before and the roofer is capable but not very experienced at this type of thing - so can someone tell me what needs to be done to stop condensation coming back down the foil pipe and into the kitchen?
    Is it as simple as creating a dog-leg and siting the roof vent offset from the extractor outlet, or is there more to it?
     
  2. DIYDave.

    DIYDave. Screwfix Select

    Strange how both your kitchen fitter and roofer haven’t got any ideas on how to deal with the possible (likely) event of condensation running back down vertical outlet duct to roof ?

    I’m diy only but have dealt with this set up several times, all with good results and no condensation issues as it runs backwards towards fan

    Ok, the above has been carried out by myself whilst fitting bathroom extractor fans but, same method stands

    Ideally, you want solid pipe from fan to roof outlet, better air flow, less turbulence means quieter fan operation, less chance of warm, moist air condensing inside vent pipe as compared to flexi ducting

    Also worth insulating solid pipe inside roof space as gets very cold up there in winter, cold pipe and air inside will all encourage warm, moist air to return back to a liquid state inside the pipe

    At base of vertical pipe you fit a ‘condensation trap’ (look these up), solvent weld to pipe, available in 110, 125, 150mm sizes - ‘most’ kitchen hoods now use 150mm duct, again, gives better extraction rates and less noise

    Any condensation that does form inside vertical pipe, runs back down to condensation trap and collects in a reservoir. This then drains via 21.5mm overflow pipe, can either drill through external wall / facia board and pop pipe outside a few inches (just like old overflow from a toilet or cold water tank in loft)

    If you do have a water tank in loft with an overflow pipe that exits outside, can ‘T’ in the new overflow from condensation trap into this existing pipe

    Adapters available for all shapes and sizes of pipe work / ducting / to suitable roof vent /

    That’s about it, hope all goes well
     
  3. SBobs

    SBobs New Member

    Thanks Dave - I’ve already looked into condensate traps but there’s nowhere nearby to run the condensate trap to.
     
  4. DIYDave.

    DIYDave. Screwfix Select

    Is there no outside wall you can drill through to poke the overflow pipe out from - it’s just 21.5mm pipe

    Or facia or soffit boards at gutter level to exit from ?
     
  5. SBobs

    SBobs New Member

    It would mean running about 7 or 8 metres of pipe or hose, to reach an outside wall.
     

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