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Mould -Indoor humidity versus outdoor humidity

  • 05-12-2014 5:55pm
    #1
    PeteFalk78
    Closed Accounts Posts: 762 ✭✭✭


    I get a small bit of mould in the main bedroom (near corner of windows) and a bit in the ensuite....nothing really bad, just normal stuff I reckon.

    I'm in the process of improving heat and ventilation in the affected rooms but I have a quick question that Google doesn't want to answer me.

    If my indoor humidity is 65-70% and outdoor humidity is higher e.g. around 80-90% today then is it counterproductive to open windows for ventilation?
    I'm just letting in wetter air...right?


Comments

  • #2
    Borzoi
    Registered Users, Registered Users 2 Posts: 2,876 ✭✭✭Borzoi


    PeteFalk78 wrote: »

    If my indoor humidity is 65-70% and outdoor humidity is higher e.g. around 80-90% today then is it counterproductive to open windows for ventilation?
    I'm just letting in wetter air...right?

    Yes and no ;-) Your measurements are of relative humidity and not absolute values. The capacity for air to hold water varies with temperature, warm air can hold more moisture than cold air. So in your case, if you allow cold air with a high RH in to the house, as it warms up the RH drops as it rises in temperature and its capacity to hold moisture increases. So relatively the humidity had dropped, allowing the air to mix with the house air and the overall humidity levels to drop. If you really want to find more, look up Psychometric properties of air.

    There are other benefits of fresh air such as reduced carbon dioxide levels and removing VOCs - all good


  • #3
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,145 Mod ✭✭✭✭BryanF


    Open the windows


  • #4
    MicktheMan
    Registered Users, Registered Users 2 Posts: 2,880 ✭✭✭MicktheMan


    BryanF wrote: »
    Open the windows

    Ditto

    - (internal) air at 20 degC and 70%RH has 12.3 grams of moisture/m3
    - (external) air at 5 degC and 90% RH has 6.1 grams of moisture/m3


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