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Controlling Humidity in Bedrooms

Joe_Adams | Posted in General Questions on

Hi everyone,

So, I have recently started some renovation jobs at my grandmother house. I am in a mixed humid climate.

The concrete and masonry house does not have a central heating/cooling or dehumidified system.

The problem is that the ceiling and walls of the bedroom where two people sleep have a considerable amount of mould.

What would be the best way to get rid of the excessive moisture. I want to apply a non-user dependent machine (e.g. dehumidifier), but I am concerned about the possible noise of extracting fans during the night.

Thank you, everyone, in advance

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  1. DCContrarian | | #1

    Dehumidifier, air conditioner or ventilation. It depends upon the conditions.

  2. Kyle Bentley | | #2

    I'd like to throw in a suggestion - measure the RH before you make any changes, so that you can at least be confident in any results that result from those changes later. Otherwise it's a feeling game.

    1. Joe_Adams | | #3

      Thank you for your reply,

      The relative humidity has been between 80% and 90%. The nocturnal period is the worst, because 2 people sleep in there with a lot of vapour production.

      1. Expert Member
        Michael Maines | | #4

        Joe, at what temperature? Most calculations assume the room is "room temperature," around 68°F, but a lot of people keep their bedrooms cool, which might affect the recommendations. For example, if the bedroom is 55° and 90%RH, raise the temperature to 70° and the RH drops to just over 50%, a relatively safe level.

  3. Douglas Horgan | | #5

    I would bet that ventilation will end up being the betters solution for this situation. Based on my experience, humidity is only one problem with closed bedrooms. They often experience high levels of CO2 as well, which dehumidification equipment won't address.
    I agree with Ken's suggestion to measure conditions and would add a CO2 or multi-instrument Indoor Air Quality monitor like the Awair I have been using.
    Ventilation is not simple or inexpensive but is likely the only good way to address all the air quality issues you'll find you have.

  4. Joe_Adams | | #6

    Thank you for your inputs.

    The bedrooms are kept fairly cold during the night, around 60F.

    I was thinking of implementing one of two options:
    1 – Heat the bedroom during the night to have lower RH values and avoid mould.
    2 – Apply an extract fan in the bedroom controlled by time or RH (I prefer RH).


    Solution 1 – Heating the bedroom during the night will allow concentrating more water vapour in the air during the night (although with lower RH). More humidity from the rest of the house will diffuse to the bedrooms. However, during the morning, I am concerned when the heating system is turned off. This is because the increased water vapour concentration will condensate more than now.

    Solution 2 – I am concerned about the noise from the fans directly in the bedroom. With so much vapour, I imagine that the fans will be running almost all the time.

  5. Steve Knapp CZ 3A Georgia | | #7


    Can you do a blower door test? If the house is really leaky, it might be worthwhile to do some air sealing so you have more control over interior conditions.

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