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Community and Q&A

Mold in closets of NZE home

Courtney McCracken | Posted in Mechanicals on

Our home is a net zero house with EUI = 13 KBTU/SF/yr in Mystic CT. It is 2000 SF, 2 stories. It has heating and cooling by 2 mini splits (one on each floor), ventilation with an HRV, and a kitchen range hood. The walls are double stud with Zip/OSB sheathing, densepack cellulose and sheetrock. We have a problem with mold in the closets.  The closets are shown on the attached drawings.  Is there a product that could be installed to deal with the mold, maybe by introducing ventilation into the closets?

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  1. Expert Member
    Zephyr7 | | #1

    My guess is you have stagnant air in the closets, and possibly also cool surfaces.

    The easiest way would be some louvered closet doors to allow for free airflow between the closet and the adjoining living space. Louvered doors are the "old school" way to ventilate closets, and they use no power at all which is a plus. They also have no moving parts that can fail and let you down. This would be the option I'd try first.

    Your next option would be small forced ventilation. I would use small 12 or 24 volt DC "muffin" fans for this, and dryer vent host and fittings. This will be more complex and less elegant than the louvered doors, but it is more flexible in placement. You only need a small amount of airflow, but you want "crossflow", so something like air coming in on the lower left front of the closet and leaving out the upper right back. The DC fans can be easily powered by "wall wart" style plug-in power supplies, and you can use small wire like thermostat wire to wire them in on the low voltage side. I would avoid the use of line voltage (120 volt) fans here for safety reasons.

    I can provide links to some suitable fans if you're interested.


    1. Courtney McCracken | | #5


      It would be helpful if you could provide the fan info. Also, any ideas on how to configure them and the dryer hose. We seldom access the closet that is the worst so the air is likely stagnant.



      1. Expert Member
        Zephyr7 | | #8

        A possible fan candidate is here:

        There are many, many options. I picked that one from a list of a bit shy of 200 that fit the basic parameters.

        I can't offer a lot of help on an installation since it depends entirely on what you have to work with. You can usually find dryer vent parts and PVC pipe fittings that you can put together to rig up what you need. It won't be elegant, but it will work. You can do a really nice job with screws and glued pieces, or you can tape things together with duct tape. Either will work.

        I'd try louvered doors first myself. You can even test if that will work by simply leaving your closet partially open for a while and seeing if that improves the conditions inside.


  2. Expert Member
    Malcolm Taylor | | #2


    What is the indoor relative humidity, and is this a seasonal problem or all year round?

    1. Courtney McCracken | | #4

      I don't have RH readings. I am not sure about the season either but the outdoor humidity is higher in the warm weather. OTOH, we are about a mile from LI sound and in the woods so it never seems to get really dry. We run the heat pump all summer set at 76.

  3. DCContrarian | | #3

    I have a similar problem at my house just up the coast in Rhode Island. I have a diagnosis but not a cure. In the summer it's humid but not hot, sometimes we get 100% humidity (which manifests as dense fog). Humidity does a better job of permeating the house than heat, so any spot in the house that is sheltered -- like a closet -- can stay a bit cooler, which can result in condensing humidity.

    The solution would be to run a dehumidifier or AC, but we prefer to keep the windows open all summer. So I don't have a solution.

  4. Scott L | | #6

    If it's a minor localized issue in a closet related to ambient humidity and no other latent water issues, and you don't want to use louvered doors, active dehumidification, fans, through-wall vents, etc. a desiccant based dehumidification solution (like Damp Rid) might work. You can buy a refillable shoe-boxed size absorber for about $20 at most hardware stores. It's basically a plastic tray with driveway salt (calcium chloride), which pulls moisture from the air, and fills up the bottom of the tray. You have to occasionally dump the liquid from the tray and add more salt. It's pretty simple and works for small local problems.

    1. Courtney McCracken | | #7

      Thank you.

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