1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Size of Hit and Miss Air Vent

Discussion in 'Building' started by HowTo, 31 Dec 2020.

  1. HowTo


    31 Dec 2020
    Thanks Received:
    United Kingdom
    Have mould issues in rooms around windows in house and have been told that this is due to lack of ventilation. Suggested solution is to fit 225mm x 225mm Hit and Miss Air vents next to the windows in each room (not enough room above window for this size vent) to have ventilation to avoid dampness and avoid mould.
    I have asked why vents need to be 225mm x 225mm as this seems big for small double rooms and single rooms. Not getting any response to my query and can't find any information online on recommended sizes of vents for room sizes.
    Can anyone help?
    Also do the vents have to be right by the window? Or can they be placed in one corner of the room just below ceiling as next to window would place vents in the middle of that walk and very noticeable at that size?
    Would appreciate any help / advice. Thanks.
  2. JohnD


    15 Nov 2005
    Thanks Received:
    Cook Islands
    Where did you hear that?

    How do you ventilate the house now, and how often?

    How old is the house?

    Which rooms are mouldy?

    Where do you dry the wet washing?

    How do you ventilate the bathroom?

    Why won't the windows open?
    • Like Like x 1
  3. Sponsored Links
  4. Harry Bloomfield

    Harry Bloomfield

    30 Dec 2018
    Thanks Received:
    United Kingdom
    All above are good questions to ask, but in addition what is the construction of the house where you are suffering mould appearing?

    9" wall, cavity wall, cavity with CWI, something else? What do you have for an heating system?

    Mould appears on walls, where there is excess moisture in a room, hitting a colder surface. Excess moisture most commonly results from drying clothes in the house, cooking and to a much lesser extent from the air you breath out. Extracting moist air at source - bathroom extract fans, cooker hoods and not drying clothes in the house help a lot.

    Adding a through the wall vent, would involve making quite a large hole in the wall, not something to be undertaken lightly. Many pre-1960's homes were originally built with these vents, to ensure fixed air supplies to open fires. Most open fires have been done away with, so they are no longer necessary and there are better ways to provide controlled ventilation.

    We have a dryer, but we never use it - because..... In summer washing is hung outside to dry, in winter it is hung to dry in out utility room, which I have set up with hanging lines, a fan to move the air and a compressor dehumidifier system. A dehumidifier with air circulation, is much more effective than heat for drying lots of damp washing.

    I added a cooker hood extracting outside and the house rule is to use it when cooking and never cook by boiling in pans without lids.

    To the bathroom I fitted an extract fan, triggered by occupation and/or humidity, plus a timer. It turns on as soon as you walk into the bathroom and then stays on for at least 20 minutes after you leave. The rule is when bath or shower is used, the bathroom window is opened onto the trickle vent position for an hour after.
    Last edited: 31 Dec 2020
    • Thanks Thanks x 1
  5. ^woody^


    3 Sep 2006
    Thanks Received:
    West Mids
    United Kingdom
    You've been given bad advice.

    Mould around windows is due to local condensation and won't be cured by a vent anywhere in a wall.

    Depending on where the mould is (what is "around windows"? Frame or reveals?) you'll need to either line the reveals to remove the cold surface of wall, and replace any mouldy silicone.

    But if the windows are steaming with condensation then that's a bigger problem and a vent in its own won't help.
    • Like Like x 2
  6. Sponsored Links

Share This Page