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condensation on windows

cekseniorceksenior Posts: 44Member
 Hi all. In the summer I installed 1/2" double cone honeycomb window treatments in my home to help with keeping my heating bills down during the winter. I've noticed this year during the heating season when the blinds are fully closed there is considerable condensation on the windows. The windows are fairly new and of Anderson brand. Ive owned the house for 9 years and only since I installed the window treatments has this happened. Is this OK or is there a simple solution to alleviate this occurance? Please excuse me of my ignorance if there is a simple solution..


  • Larry (from OSHA)Larry (from OSHA) Posts: 684Member
    edited January 2010
    wet windows

    You are doing the right thing to keep the heat in a little better by closing the shades, but with that you are very likely to get condensation because the cooler air next to the windows can't hold as much moisture as the warmer air on the other side of the shades. 

    It's really a catch 22 situation where you want to add humidity in the winter, but to keep the windows free of condensation, you need less humidity. 

    Google window condensation and you will find the recommended level of moisture in the air based on outside temp.  It's a lot less than you would think. 

    I just put in new Pella windows this fall and deal with the same issues.  Air movement across the windows and opening the shades during the day helps a lot.

  • TomSTomS Posts: 46Member

    The first thing to check is if the excess moisture is coming from a cracked heat exchanger or venting problem of your furnace.
  • GordyGordy Posts: 9,264Member
    Any room

    In paticular that are worse then others?  Say the bedrooms that are occupied, bathrooms, kitchen?

    What kind of heating system do you have? F/A, RFH

  • Jamie HallJamie Hall Posts: 10,453Member
    Hard to win

    in this situation.  If any surface is colder than the dew point of the indoor air, water will condense on it -- guaranteed.  Putting up the blinds will save heat, but inevitably the windows will now be cooler.  And the water will condense if the humidity is high enough.

    Your only solution is to tolerate lower humidity, or warmer windows (more heat loss).  I wouldn't worry too much about trying to find leaks or anything like that.

    Sorry about that... oh, and it doesn't matter what the heating system is.  They will all do it -- forced air, hot water, steam, wood, doesn't matter.  It's simply the relationship between the relative humidity of the air, the overall air temperature, and the temperature of the surface.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • cekseniorceksenior Posts: 44Member
    All rooms

    That have the new honeycomb blinds have sweaty windows. I have a combination steam and hot water loop setup in my home. Just like Jamie Hall says either steam or hot water it still sweats up the windows. Funny thing is that the humidity is very low in the house (29%) becuase the heat is comming up good becuase of the frigid temps here in Queens NY. My only concern is damaging the wood around the windows becuase of the water building up. It does clear up cracking open the blinds but it seems counteractive. Keeping the warm air in and the windows sweat crack the blinds let hot air hit them and loose the nice tight envelope in the process..Definately a catch 22.
  • Tim McElwainTim McElwain Posts: 4,234Member
    Have some vents

    put in the soffits in the house. The house is probably too tight and is not getting enough ventilation especially with only 29% humidity.
  • GordyGordy Posts: 9,264Member
    edited January 2010
    My own experience

     Get the humidity down to around 20% you will see a noticable improvement.

    All though 30% is recommended we don't notice any  discomfort around 20%.

    FA systems do tend to have less humidity with out the addition of a humidifier in the system.

    There are differences among types of heating systems in that Radiant does tend to have a higher RH in the home. I have lived with FA, and it always seemed to be much drier to the point of needing humidification.

    Controled Ventilation is key with showers, cooking, cleaning,laundry, done any painting?and the human component. There is much moisture being put back  into the home. Bedrooms,bathrooms, and kitchens are key areas.


    In my own home 50's construction with ceiling, and floor radiant.  I go through the same scenerio until it gets down in the teens, and I burn a few fires in my masonary fireplaces. That gets the RH down to 20, and the house is good to go. 

  • cekseniorceksenior Posts: 44Member
    Uninsulated walls

    Cause the heat to always be cranking in this house when its cold. Too me its uncomfortably dry at 30% humidity.  We all wake up with dry mouths, noses and coughing becuase of the dry air. Any drier would be down right unbearable.

    And although the boiler doesen't run as much with these new blinds installed I'm not sure I like the trade off of wet windows and sills. There is no doubt over time it will cause damage.

    The one room with the old mini blinds the windows and sills are bone dry. So there is no doubt that with the addition of these blinds is causing the moisture condition.

    So do I keep the blinds open and waste energy or close em up save energy and have wet windows and sills. Who new adding these new blinds would cause such a problem.
  • Jamie HallJamie Hall Posts: 10,453Member
    Sorry old boy

    but if my experience is anything to go by, you will be much happier in the long run if you can manage to keep the humidity up in your bedroom, and let it drop to the point where it doesn't condense (as mentioned, it may well go to or below 20%) -- or keep the blinds up enough to avoid the condensation at the higher humidity.  Particularly with uninsulated walls.

    You see, not only are you seeing condensation on the windows and sills, which will rot them out remarkably quickly (trust me: I am the building super for a "cottage" turned into a museum, which I am restoring to its original condition, and I have replaced more sills than I care to mention) but you are also, at the higher humidiy, getting condensation in the walls -- which is rotting those out, too, only you can't see it...

    It is a tough tradeoff, particularly in these days of heightened environmental consciousness.  But my choice would be the low humidity.  I might add, though, that you can help a little by keeping the overall air temperature down and bundling up.  The relative humidity can be a little higher then -- and thus more comfortable -- before you get condensation, and you can save energy by the lower temperature.  For example, if you are getting condensation with a room air temperature of 72, the relative humidity is probably no higher than 34% -- but if you dropped the temp to 65, the relative humidity could be as high as 43% before you got condensation at the same outdoor temperature.  Much more comfortable.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • A question for cek

    Just a thought,

    Do you have any unvented gas appliances in the home. Gas fireplace, gas heater, etc?

    Ed Carey
  • cekseniorceksenior Posts: 44Member
    No unvented appliances.

    Most of my friends laugh when I tell them I keep my whole house at 66 degrees at all times. To me its quite comfortable.

    Am I missing something here or is just posible that these blinds are doing exactly what they were designed to do. That being they insulate the window openings and the trade off is damp windows? I wonder if anybody else with insulated blinds has this problem.

    Like I said the one room with mini blinds dosent have this issue. And the basement windows dont suffer from this either.
  • TRobTRob Posts: 20Member
    Whence the wet windows?

    My theory here is that the windows are the vapor barrier. Without the insulated blinds, the inner surface of the window glass is warm enough to be above the dew point of the interior with 20%, whatever, relative humidity.  With the blinds closed, they are doing such a good insulating job that the glass surfaces are now cooler than the dew point, hence the condensation. (Another case of unanticipated consequences!)
  • Jamie HallJamie Hall Posts: 10,453Member
    CEKSenior, The blinds

    are indeed doing precisely what they are advertised to do (more's the wonder!).  Trouble is, nobody bothers to mention that in the process they can allow the window surface temperature to drop below the dew point.  TRob's theory is correct.

    Drip drip drip...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Larry WeingartenLarry Weingarten Posts: 1,494Member

    Hello:  It seems to be agreed on that condensation forms because the interior of the glass reaches dewpoint.  Anything involving warming up the glass either does it by throwing away energy or by using better glass.  There is another approach which would be to shutter or otherwise cover the glass outside.  That way you get to keep both the heat and humidity.  I'm involved with Synergistic Building Technologies which is developing insulated shutters, so have been looking at window heat loss/gain.  There really is nothing for sale yet, so this is not an ad, but you might find some useful ideas there.

    Yours,  Larry
  • GordyGordy Posts: 9,264Member
    edited January 2010

    Open the blinds on sunny days taking advantage of solar gain, and close them at night.  Run the ceiling fan while they are open to dry the windows. At least the moisture has not turned to ice. Seen that happen in some houses!

    Blow insulation in the walls!!

  • GordyGordy Posts: 9,264Member

     When I was in Italy outside roll up shutters were the norm on alot of residences. Good Idea another layer of protection.

  • cekseniorceksenior Posts: 44Member
    Thank you all for your input

    As always when I ask a question on The Wall I get plenty of knowledgeable advise and input.

    I'll have to do some tinkerin' to alleviate this problem. But Hey, what would home ownership be without problems that need to be solved...Boring.
  • Mark EathertonMark Eatherton Posts: 5,844Member
    The trick....

    is keeping the glass surface temperature above the dew point, and THAT is a trick.

    Now with Power e Radiant Glass windows, it is not a trick, but you already spent money on windows, so I am a day late and a dollar short.

    So, if you can't control the glass surface temperatures, then you have to control the humidity levels within the dwelling.

    Heres a link to a web site that shows where the dew point is for differing glass configurations. Essentially, if you can maintain a glass surface temperature of 70 degrees F, then dew can not form on the surface, even at humidity levels approaching 100%.


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • GordyGordy Posts: 9,264Member
    70* glass temp

    Now that is a trick, cause ya know we don't have the fancy Power e glass windows you sport.

    I like the chart I will save that very handy, Mark your like the internet librarian.

  • RoyboyRoyboy Posts: 220Member
    edited January 2010
    its a tough one

    if cold air can "drain" out from behind your shades, you end up with a nice convective airflow where the cold air that leaks out is continually replaced at the upper portion of the shade by warmer air from the room, which can then leave some of its moisture on the glass if its below the dew point. I've read studies that purported to show increased heat loss out of windows with interior shades when shades were drawn because the convective airflow was so strong behind the shade.

    only ways to deal with this are somehow warm up the interior window surface (lacking ME's futuristic warm windows, how bout a good old-fashioned exterior storm window?), figure out a way to keep air from flowing around the edges of your honeycomb blinds, or reduce humidity as already mentioned. high-performance window insulation will always have some variety of "edge-seal" to block airflow. the bottom of the honeycomb blinds will generally seal pretty well to the sill, but the edges are tough to seal.

    I've seen some honeycombs that run in U-shaped tracks on the sides - that might well work pretty well if the tracks are tight enough to the blinds. perhaps you could try figuring out some sort of U-track that would fasten to the sides of the window frame and, if sized properly, might greatly reduce airflow even if it doesn't stop it entirely. you can probably tell how well anything is going to help by just feeling how strongly the cold air is flowing out at the base of the blinds, compared to one you haven't modified.

    good luck and it would be interesting to hear if anything works for you as this is not an uncommon problem.

  • Kevin_in_Denver_2Kevin_in_Denver_2 Posts: 588Member
    Sealing Honeycomb Blinds

    I tested those blinds a few years ago with the U-shaped track. There was no improvement whatsoever in the amount of condensation.

    What's worse, all that condensation caused mold to grow in the blind material. I was able to salvage them by washing with bleach, but they were almost ruined.

    I know that Hunter Douglas tested mylar material and spring-fitted side seals to help with this leakage, but they never went into production.

    I think there is a manufacturer of window quilts with mylar inside and magnetic perimeter seals, and that would work.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • RoyboyRoyboy Posts: 220Member
    thanks Kevin

    that's good to know. one more option scratched off my list of how to insulate my own big south-facing fixed doublepane glass that's great on a sunny winter day but bad news on those long winter nights ...

    Larry W - need a n WI test site for your exterior shutters?
  • RoyboyRoyboy Posts: 220Member
    Kevin - is this the shade you installed?

    ... looks like it would make a pretty good seal ...
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