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Thread: How to stop moisture condensation

  1. #1
    Join Date
    Nov 2011
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    How to stop moisture condensation

    We have ADU, 2 story building with approximately shy of 1000 sf 2 bed on the 2nd floor.
    Originally, it had Cadet heaters. Total junk.
    My son lives there.
    4 yrs back, I had Mitsubishi mini splits installed there. 1 center ceiling unit and 2 wall mounts in bedrooms.
    It was all fine, until he married. As of the last 2 yrs by now, they have serious water condensation on windows, along with mold build up. Particularly, in their bedroom.
    They normally keep temp at 70 and DIL laundries non stop, as she needs fresh clean sheets for her work.
    Last year, I had contractor look at the mold issue. We agreed that, it's leaking window frames, what was almost the case. When windows trim was removes, there was very poorly done water proofing and trim boards were rotting.
    Windows were resealed, trim replaced with hardie board. It all appeared to be fine - we are back to the same problem. Glass is covered in water condensate from the inside, mold in corners.
    At night, they keep bedroom door shut, to prevent cats from getting in.
    Well, son bought a house and is closing in 3 weeks.
    We want to rent the place but, clearly, need to fix this issue.
    My theory is - lack of air circulation+too much heat inside. We live in Pac NW, fall and spring are rains non stop.
    I feel, as heat pump is only pushing air IN, and there are no ducts, it, basically, creates hot, humid air inside that does not go anywhere. Building has attic.
    What recommendations do you have?

  2. #2
    Join Date
    Dec 2004
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    Sounds like you need a whole house dehumidifier, and some form of ventilation.

    But also you mentioned non stop laundry.

    Is the dryer not exhausted properly?


    Sent from my iPhone using Tapatalk

  3. #3
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    Thread Starter
    I just went there and looked at it. It's in their bedroom only. I left window ajar and cracked the door open. Sort of jammed it so that cats don't get in. I'll see what happens.
    No, dryer vents fine, I see steam coming out the vent outside.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Moisture buildup is usually a sign a lack of fresh air change. A person exhales .25 lbs. of moisture per hour. We know that they are getting some fresh air because they have not died. As the fresh air passes through the interior space, the occupant moisture is added to the exfiltrating air.

    The infiltrating fresh air has outside moisture, damp-to- dry. The slower the air change rate, the higher the mixed moisture level.

    Steps to take.

    You could confirm the fresh air change rate by monitoring the CO2 levels of the inside air. One person inside a space getting 50 cfm of fresh air raises the outside fresh air from 450 PPM CO2 to 650 PPM. The interior moisture level will outside plus the moisture from the occupant. Moisture is more complex because of the moisture in the materials inside the occupied space.

    For good indoor air quality, you need a fresh air change in 3-5 hours to purge indoor pollutants and renew oxygen. When the outdoor dew point less than you want inside, expect the needed fresh air change to dry out the occupied space. In a big home with low occupancy and very low outdoor dew point of cold climates, the home will need humidification for comfort. No problem in the wet part of NW.

    Next problem. The indoor moisture condensation problem is increased because of lack uniform heating of the materials exposed to the more moisture indoor air. Keep the windows warmer by maintaining inside temps 24/7 will decrease the condensation on any of the cooler materials that interface with the outdoor temperatures. Do not setback the T-Stat during cold weather.

    You will also find dust mites in homes with this moisture level. This the most common allergn for people.

    Also if all else fails, consider adding a small whole house dehumdifier that will add some fresh air and maintain <50%RH during peak outdoor dew points.

    Here would be hit list.

    Start by maintain 68^F 24/7 to avoid any visible condensation. Next, crack window and operate bach fans to reduce the moisture level even when it is raining outside. Remember that the inside dew point is the outside infiltrating air plus the moisture occupants add. More air change always reduces the interior moisture levels.

    Play with the basics and then post your thoughts about our suggestions.
    Keep us posted. This is big problem in climate zone. It keep many allergist in business.

    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. Likes ukrkoz, baby b, thatguy liked this post.
  6. #5
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    Thread Starter
    Oh wow! Thank you.
    As I mentioned, as they are gone for 4 days, I'll keep that bedroom air circulated between the ajar door and window. If it helps, they will need to rethink steamy nights in small bedroom with heat at 70 and doors/window shut closed.

  7. #6
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    Quote Originally Posted by ukrkoz View Post
    Oh wow! Thank you.
    As I mentioned, as they are gone for 4 days, I'll keep that bedroom air circulated between the ajar door and window. If it helps, they will need to rethink steamy nights in small bedroom with heat at 70 and doors/window shut closed.
    Nothing wrong with periodic high humidity. The damage is done when extended beyond 6-12 hours. That grows mold.

    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. Likes baby b liked this post.
  9. #7
    Join Date
    Jan 2005
    Location
    St. Lucie West, FL.
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    What Teddy says goes. Nothing worse than having home with humidity and condensation issues. Bigtime Health hazard and remediation to fix after damage is done. Nightmare to clean mold and Mildew.

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