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  1. #1
    Join Date
    Jan 2012
    Location
    Indiana
    Posts
    36

    Condensation on windows only w/ temps 20F or lower

    Greetings,
    I'm getting condensation on all my dual pane wood casements when the outside temp. is 20F degrees or lower. Otherwise the windows stay dry. The humidity in the house is 35% to 38%. This two story house was built in 2000 and I recently insulated the attic with closed cell foam and cellulose, but I've had this problem since I moved in this house 6 years ago.
    Is this a sign of too much humidity or just poor performing windows? I don't think that my humidity level was too high or is it ?

    This house is equipped with a high efficiency gas furnace that does not draw fresh air from the outside. Gas stove and electric dryer. All bathrooms have functioning exhaust fans that are used after showers.

  2. #2
    Join Date
    Feb 2011
    Location
    North East Ohio
    Posts
    741
    do you have a humidifier on the furnace? This is happening because the humidity level outside drops as the temp drops. The humidity level inside stays fairly constant. As the difference inthese levels becomes greater the inside moisture condenses on the windows. If you have a humidifier on the furnace turnn it down when the temps drop. Good luck

  3. #3
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,384
    Quote Originally Posted by NCHeat View Post
    do you have a humidifier on the furnace? This is happening because the humidity level outside drops as the temp drops. The humidity level inside stays fairly constant. As the difference inthese levels becomes greater the inside moisture condenses on the windows. If you have a humidifier on the furnace turnn it down when the temps drop. Good luck
    Condensation on the windows has nothing to do with the humidity OUTSIDE.
    It is the TEMPERATURE difference on the windows and the RH inside that matters.

  4. #4
    Join Date
    Feb 2011
    Location
    North East Ohio
    Posts
    741
    Quote Originally Posted by kdean1 View Post
    Condensation on the windows has nothing to do with the humidity OUTSIDE.
    It is the TEMPERATURE difference on the windows and the RH inside that matters.
    tomato tamoto

  5. #5
    Join Date
    Jan 2012
    Location
    Indiana
    Posts
    36
    No humidifier anywhere in the house. I run a dehumidifier in the basement set at 45% which runs all the time until the outside temps get in the 20's. Then it will shutoff.

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,399
    Could be the windows. My humidity rarely drops below the mid 30s so even with temps in the single digits I never have moisture on the windows. Of course, experts would say humidity 35% in 5 weather is too high. Might have to introduce some outdoor air like through a simple vent or maybe an ERV/HRV. Or if humidity is high year round, a ventilating dehumidifier.

  7. #7
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    Does this happen to the windows that have blinds closed overnight or to bedroom windows where poeple are sleeping?

  8. #8
    Join Date
    Jan 2012
    Location
    Indiana
    Posts
    36
    Quote Originally Posted by thermojohn View Post
    Does this happen to the windows that have blinds closed overnight or to bedroom windows where poeple are sleeping?
    All the windows have wood blinds that are left open except in the bedrooms. I can see the bedroom windows sweating but I have a problem with rest of the windows. I even raise the blinds that are left open a few inches to no avail.

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,065
    Quote Originally Posted by Tta197 View Post
    Greetings,
    I'm getting condensation on all my dual pane wood casements when the outside temp. is 20F degrees or lower. Otherwise the windows stay dry. The humidity in the house is 35% to 38%. This two story house was built in 2000 and I recently insulated the attic with closed cell foam and cellulose, but I've had this problem since I moved in this house 6 years ago.
    Is this a sign of too much humidity or just poor performing windows? I don't think that my humidity level was too high or is it ?

    This house is equipped with a high efficiency gas furnace that does not draw fresh air from the outside. Gas stove and electric dryer. All bathrooms have functioning exhaust fans that are used after showers.
    As temp outside decreases, the window glass temperature drops below the dew point of the air in the home. Occasional moisture on the glass is not a problem unless the moisture drips to the frame for an extended time.
    As outside temps drop and winds rise, your home increases natural ventilation. Ideally, homes need a fresh air change in 4-5 hours to purge indoor pollutants and renew oxygen. In a 2,500 sqft. home, the ideal air change is 60 cfm of fresh air. When the outdoor air is 20^F as a low, the outdoor dew point is <20^F. 60 cfm of 20^F air passes through your home and is humidified to a 40^F dew point, 1 lb. of moisture is removed.
    To eliminate mositure on the glass raise the glass temperature or decrease the dew point of the inside air. Increasing fresh air ventilation slightly or raising the temperature during cold weather are solutions.
    Your house works well at +20^F. If there are <3 in the home, you are not getting enough fresh air naturally to purge indoor pollutants at warmer temperatures because of decreased natural pressure from wind and warmer temperatures. Adding 60 cfm of fresh make-up when the home is occupied would improve the indoor air quality during the calm times of the year and fix the window condensation problem. This would increase your heating/cooling cost <$100 a year. You may need an upgrade on your dehumidifier to something like the Santa Fe/Ultra-Aire for mild season humidity control.
    Short term, try cracking a window to clear the windows or raise the t-stat a couple degrees during cold weather evenings.
    Keep us posted.
    Regards TB
    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"

  10. #10
    Join Date
    Jan 2012
    Location
    Indiana
    Posts
    36
    Teddy,
    Do I need to address the air inlet to furnace so that it's sucking outside air or is that over kill? It would be a bit of a pain to drill thru my rim joist because the house is all brick. So I would have three penetration points, one for the furnace inlet and two for the Hrv. Correct?

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Cosmicmuffin, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,065
    Quote Originally Posted by Tta197 View Post
    Teddy,
    Do I need to address the air inlet to furnace so that it's sucking outside air or is that over kill? It would be a bit of a pain to drill thru my rim joist because the house is all brick. So I would have three penetration points, one for the furnace inlet and two for the Hrv. Correct?
    Do you have a HRV? If so, operate 24/7 on high until the windows clear. You do not need both HRV and a fresh air inlet on the furnace. Also make sure your HRV is functional. High speed should make the air inlet and outlet of the HRV noticeable.

    Keep us posted.
    My points are that most homes need a only a slight increase in cold weather fresh air ventilation and are probably best served by the make-up air inlet instead of a HRV. Most homes need significant simple mechanical fresh air ventilation during the other three seasons. There is very little saving during the mild seasons. Also clothes drier, kitchen hood, and bath fans need make-up air to function.
    All this said, if you have a HRV operate year around when the house is occupied. There limitations to balanced flow ventilation but is certainly adequate in most cases. Maintain a good dehumidifier to maintain <50%RH throughout the home.
    Regards TB
    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"

  13. #13
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,482
    I suspect your humidity level is higer than you gauge is reading. Regardless, I think you need to introduce some fresh air into the home.

    It might not take that much. The least expensive way is to run a pipe (size to be determined) from the outside to the return air duct with a damper control.

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