window condensation


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Old 12-04-06, 06:46 PM
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window condensation

We are having a problem with condensation on our windows. We have window quilts that, when down, insulated our rooms nicely. However, if we leafe them down condensation forms on the windows, and when cold enough even freezes. Is there a good way to seal these windows, or some other way to allow us to leave the window quilts down without forming condensation? The condensation gets so heavy that water actually drips from the window ledge. Any help would eb greatly appreciated. Thanks.
 
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Old 12-04-06, 07:25 PM
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windows with condensation is allways a ventalation problem. But yours could be a lack of air movement! Id remove your covers and see if problem goes away.
 
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Old 12-04-06, 08:21 PM
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Your window quilts are a two edged sword that help one problem but create another. They may keep the house warmer by preventing warm air from exiting out the windows, since glass has a terrible r-value. But they prevent heat from the house from warming the glass in the winter and potentially keeping the glass temperature from dropping below the dew point- the point at which water vapor will condense.

You can do 3 things.

-leaving the window quilts up will warm the windows, reducing the liklihood of condensation.

-reduce humidity by lowering the thermostat a few degrees (warm air holds more moisture than cooler air), run a duhumidifier nonstop (and keep it emptied), take baths instead of showers (also reduces humidity in the home).

-point a fan at the window(s) in question to circulate warm air over the window, preventing it from getting too cold.

A 3M window kit installed over your window trim might help, or it might not. If you have a storm window on the exterior of the windows, make sure the storm window is shut.
 
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Old 12-05-06, 07:07 AM
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Window quilts and condensation

Unfortunately window quilts are the worst type of window treatment I can think of regarding the formation of condensation and ice. Like XSleeper mentioned, they help with one issue (extra insulation) but create another (more prone to condensation). The reason is because the "extra insulation" is in the wrong place: between the glass and the interior of the home, instead of between the glass and the cold. I'm going to throw a lot of statistics at you to address condensation/ice buildup on your windows. Keep in mind that these stats are based on a worst-case scenario of 0 outside and 70 inside, which sounds like it may apply to your climate but is not applicable to warmer, southern climates.

Now for some stats. If a window is clear double glazed insulating glass (doesn't matter if it's wood or vinyl), the center-of-glass roomside temperature would be about 44-45F. (Incidentally, single pane windows with a storm window would be about the same) Adding a Low E coating to the glass bumps it up to about 52F, and Low E insulating glass with Argon gas raises the glass temperature to 57-58F. Not bad for 0 outside.

However, with insulating glass the edge-of-glass temperatures are much lower than center-of-glass. The type of spacer that separates the panes of glass greatly affects the edge temperature, and much could be said about the merits of different types of spacers. Naturally, condensation, and even ice, would normally occur at the edge first, since that's the cold "weak spot." Clear IG with an aluminum box spacer has an edge temp of only about 29F. Low E glass with an aluminum spacer only raises it to about 32. Then there are "warm edge" spacers, which are warmer and provide more condensation resistance. Stainless steel spacers are about 37 edge temp on a Low E/argon unit, and presumably (don't have exact stats on this) Superspacer and TPS would be at the top at 39-40. Again, warm edge spacers typically range from 35-40, but still tend to max out usually in the upper 30s. With single glazed windows that have an exterior storm window, the edge of glass is a bit lower but not as severe a drop as insulating glass.

Now for the fun part. If you cover a Low E/Argon gas unit with some type of roomside window treatment such as a pleated shade, the center-of-glass temperature drops from about 57 to only 36. That's an amazing 21 drop. I don't have any exact stats on what that does to the edge temperature, but I would imagine it must drop 5-15 as well. The reason it drops is because the air in the room is no longer freely circulating against the glass. A window quilt, if anything, would make it worse. Even a couch or desk in front of a window will significantly reduce the glass temperature if the furniture is partially blocking part of the window.

Enough stats. Condensation, and worse yet, ice, can NOT occur unless two conditions are present at the same time: high humidity and cold temperatures. The cold temperatures on your windows could be due in part to missing or defective weatherstrip, poorly-fitting windows, faulty installation, or just because of cold winter weather. If you have cold weather but low humidity, condensation can not occur, even with window quilts. Both have to be there. If you're experiencing condensation/ice buildup on your windows, you have too much humidity given the current outside temperature with the existing glass system that is in the home (assuming that the windows are properly installed and not defective in some way). There are TWO basic solutions: raise the glass temperature or lower the humidity. That's it in a nutshell - those two things. More about those in a bit. First, I'd buy a digital hygrometer from Home Depot, Radioshack, a hardware store, etc. to measure the amount of humidity in the house (about $10-$29). You need to know that. Then I'd visit a window company's website for recommended humidity levels for various outdoor temperatures. Most window manufacturers also have brochures on condensation and recommended humidity levels. Many home humidification systems have a guide shown right on the humidistat control. Most of them will state that when it's 0 degrees outside your humidity level inside should be in the 20-25% range.

RAISE THE GLASS TEMPERATURE - There are many things that can be done to raise the glass temperature. A key one for you is to raise the window quilts up when it's really cold out. As mentioned before that can increase the glass temperature by an additional 21 or more, but unfortunately that negates one advantage of having window quilts. But you're stuck with them, so you'll have to make the best of the situation. A compromise is to open them just slightly, maybe 4" to 8", so that warm air can circulate against the bottom of the glass (the most condensation-prone area) and partially warm the glass unit. For old existing windows, the best solution is often to replace them with modern, energy-efficient windows. If you do some day replace your windows, it would be advisable to get warm-edge spacers, Low E coatings, and gas filling in the unit to hopefully avoid condensation, and preferably NOT use window quilts anymore. Other ways to raise the glass temperature include taking out roomside casement screens during the winter, using free standing fans or ceiling fans to better circulate air against the glass, and adding another layer of glass or plastic (I hate to see that though - it shouldn't be necessary).

LOWER THE HUMIDITY - I haven't seen any previous posts on reducing humidity, but if they exist could someone please post a link to that topic? One of the best solutions for an airtight home is to have an air-to-air heat exchange ventilator installed to the furnace. It's required by code for new homes in some areas. It brings in the DRY fresh air from the outside and exhausts the stale HUMID air - giving you healthy air to breathe and lowering the humidity to the desired level. New homes are built so much more airtight than older homes, so they often need mechanical help to get air exchanges. Older homes exchanged air by being drafty. Dehumidifiers will help too, but are not as effective, since they usually can't get the humidity low enough. Great for basements though. Other ways include running exhaust fans when showering (and leave them on for a while), or simply stop bathing ;-)

In summary, condensation on windows can and will occur under the proper conditions. Even ice can form if the humidity is high enough, the temperature is low enough, and other factors are in place such as restricted airflow to the glass because of window quilts. You need a humidity-measuring device to see if your humidity is too high. And ultimately somebody has to address raising the glass temperature or lowering the humidity.
 
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Old 12-05-06, 02:18 PM
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Simply breathing throughout the night causes massive amounts of condensation on the glass in the morning, and promotes the growth of black mold on the window sills. I can't imagine any solution to the problem, since my rooms are painted with several coats of oil primer, which is as much a vapour barrier as anything. I presume leaving bedroom doors open at night can improve the situation, but that's a matter of noise control rather than heat or moisture.

J
 
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Old 12-05-06, 03:45 PM
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Great stats, Tru_blue. Everything changes when you don't have 70F air on the interior side of even the "best" window.
 
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Old 12-05-06, 04:28 PM
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Wink Words

Thanks XS. Of course you said the same thing as me in 1/4th the time. You're just more "efficient."
 
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Old 12-05-06, 05:28 PM
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Turn your fan to on will help some.
 
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Old 12-06-06, 08:40 AM
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Improving air circulation so that window is well ventilated and has the opportunity to receive some heat will help. Reducing humidity in the home will also help with condensation. When warm, moist air makes contact with cold surface, it condenses.

Humidity should be maintained between 35-55%. If higher, you can run a dehumidifier. Running vent/fan units over kitchen stove and in bathrooms will help. Running vent/fans for 20-30 minutes after cooking and bathing removes excess humidity.
 
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Old 12-06-06, 11:08 AM
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thanks

for all the help. Is there any sort of film or something of that nature I can stick to the window for better insulation? (other than the 3m shrink wrap stuff) the windows are rather large and the way they are set up makes the 3m method very hard to do properly. I have been keeping the quilts partially open and that does eliminate the condensation. Thanks again.
 
 

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