# Sweating windows



## big daddy-o (Jan 2, 2008)

My home is just turning 5 yrs. old, i have had sweating windows from day one .(Anderson) company says to much humidity, I run a humidifier in winter so house in'st to dry, but then windows drip water 24/7. any help?


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## concretemasonry (Oct 10, 2006)

You get condensation on the panes from too much humidity and/or poor air circulation around the windows.

Depending on the outside temperature, you can very easily get too much humidity if you run a humidifier too much.


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## skymaster (Jun 6, 2007)

Turn OFF the humidifier and give it a week or so and see if your problem goes away. The humidity is trapped inside and no way to dissapate. Sounds like you may want to check the installation of those windows for air infiltration


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## mcvane (Mar 19, 2007)

*window sweat*

Do you know what kind of windows you have?

We have cheapie contractor windows on the main floor that are not thermal/argon gas insulated in between the double glass.

Because of that, if we have a hot meal cooked in the kitchen, the humidity shows the condensation - it might simply be that.

Upstairs, we installed good quality windows that have the gas - there is no condensation there.

Maybe this is your situation?


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## big daddy-o (Jan 2, 2008)

these windows are the cheap builder series Anderson. every window in the house even the basement, they are the plain jane no argon gas type. this is the time you wish they would have tried to sell me an upgrade , but they didn't.lol......


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## mikey48 (Dec 6, 2007)

We have double paned windows and have no problem with them in the Northwest. With all the rain we have it very humid.


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## skymaster (Jun 6, 2007)

Big: This may sound crazy but call Andersen, take measurements of a few window sashes, the part you move with the glass in em. It is very possible you can buy new sashes that are good thermopane and just pull out the old crap and put in the new,without any muss or fuss


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## troubleseeker (Sep 25, 2006)

skymaster said:


> Big: This may sound crazy but call Andersen, take measurements of a few window sashes, the part you move with the glass in em. It is very possible you can buy new sashes that are good thermopane and just pull out the old crap and put in the new,without any muss or fuss


 That is probably so, but he should not have to replace sashes in a "premium brand" window, as Anderson is marketed to be, just to get the quality he should have from the beginning. My point is that many products build a reputation on premium performance, then use the name reputation to start selling crap lines to compete in the price wars. Sadly, most homeowners, and an awful lot of contractors also, buy premium branded products based on established reputations when they really were premium products, and are not aware that many of them have been "dumbed down" for price reasons


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## Kingfisher (Nov 19, 2007)

If as a "pro" you don't know that single pane windows sweat, you should really change jobs:laughing:


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## skymaster (Jun 6, 2007)

Trouble: I agree but the damn horse is outta the barn. I was just trying to think of a solution the the problem.
KinFisher: I wasn't going there:whistling2: However I think a closer inspection before buying would have been a good idea.


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## oldfrt (Oct 18, 2007)

big daddy-o said:


> these windows are the cheap builder series Anderson. every window in the house even the basement, *they are the plain* *jane no argon gas type*. this is the time you wish they would have tried to sell me an upgrade , but they didn't.lol......


 I see plane jane no argon gas,not single pane units here.

If they are indeed a double pane glass,and your are running a humidifier,your going to have problems.The moisture is carried by the heat trying to escape the house,the windows being the less resistant to heat loss is where that moisture will stop.If there was air infiltration,then there would be heat loss through this area and the moisture would escape with the heat.
Do cut back on your humidifier until the problem stops.


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## mikey48 (Dec 6, 2007)

I agree, it a moisture problem in the home. This home should also have a ventilation system either on the central heat system or the bathroom should have timers on their vent fans so the come on once a day. Also if this home has a crawl space below it and it has a moisture problem that would also cause it. I have also seen small homes with lots of people living in it also causing these people.


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## oberon (Apr 29, 2006)

You have interior condensation on your windows simply because the surface temperature of the window is below the dew point temperature of the air in your home…that’s it…a very simple explanation.

Unfortunately, as to why the surface temperature of your window (glass) is below the dew point temperature of the air in your home may be a bit more complex – so I am going to offer a few thoughts and maybe even throw in a few numbers that I hope might help your situation. 

In the summer, when you pull something cold and refreshing out of the refrigerator, and the air is warm and humid, that cold and refreshing beverage container suddenly and quite magically becomes instantly wet – just as soon as it is exposed to the air. What has happened is that the temperature of the container fresh from the refrigerator is below the dew point temperature of the air – which has caused condensation on the outside of that container.

What happens to your windows in the fall and winter is that the surface of the glass is below the dew point temperature of the air in your home – which is causing condensation on the surface of that glass.

Dew point is defined as saturation vapor density...or put in simpler terms, when the air reaches 100% relative humidity and can hold no more moisture. 

Relative humidity is, well, relative. 

Relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature. Put a bit more simply, dew point is 100% relative humidity or the point where the air - at that temperature - is no longer able to hold any more moisture. If the air has reached vapor saturation (100% relative humidity), then the air will release moisture...be it on the outside of that cold beverage container in the summer time, or be it on the interior glass surface of your windows in the winter time, it makes no difference. If the surface temperature happens to be below freezing, then that moisture becomes frost or even ice.

In order to stop condensation from forming on the surface of a window, you either have to lower the dew point temperature of the air in your home to a level below the dew point temperature of the window surface, or you have to warm up the window surface to a temperature above the dew point temperature of your home, or a combination of both. 

Lowering the _relative humidity_ of the air in your home may have absolutely no effect on controlling window condensation or it may completely solve your problem – depends on how you lower the relative humidity and what affect the “how” has on both the moisture level of your air and the temperature of your windows. All this because there are two ways to lower relative humidity – first, you can increase the air temperature in your home or second, you can decrease the moisture content of the air in your home. 

By increasing the air temperature in your home you _will_ lower the relative humidity but you _will not_ change the dew point – which is based on the amount of water vapor in the air and is not based on the temperature of the air. So, while the RH is lower with higher air temperature, it may not effect condensation on window surfaces at all – unless the rise in air temperature also caused a corresponding rise in window glass temperature to a level above the dew point temperature. 

But, lowering the amount of water vapor or moisture in your air will lower the dew point temperature as well. And if it lowers the dew point temperature sufficiently to drop it below the temperature of your window glass – no more condensation issues.

The amount of moisture in the air is measured in grams per cubic meter, which is kind of nice for our metric folks but not so nice for our non-metric folks; but the metric version is much easier on the calculator than the English version. However, in the interest of making this stuff easier to understand for all of us non-metric types, I am going to use Fahrenheit rather than Celsius temperatures in the calculations. 

Okay – consider your home at 65 degrees F and with a relative humidity reading of 40%. There are 6.25 grams of water in a cubic meter of air in your home in that particular scenario - which then equates to a dew point temperature of 38 degrees F. So at 38 degrees the air will be at 100% relative humidity or at saturation vapor density. 

Now, if your neighbor keeps her house at 75 degrees, but she also has 6.25 grams of water per cubic meter in her air, then the relative humidity in her home is 29% - versus your 40%. But, and here’s the kicker, the dew point temperature in her home is still 38 degrees. 

While the relative humidity in her home is much lower than is the relative humidity in yours; if the surface temperature of the windows in her home is 35 degrees she will have condensation on those windows…yet if the surface temperature of your windows is 40 degrees – only five degrees warmer – you will not have condensation on your windows. 

So, while her handy humidity gauge reads (correctly) only 29% RH – she has a condensation problem....while your handy humidity gauge reads (correctly) 40% RH – you don’t have a condensation problem…SWEET…well, for you anyway, not her. 

If your home hygrometer measures the relative humidity in your home at 60% while the temperature of your home is 70 degrees, you will have a dew point temperature of about 51 degrees – meaning that if the temperature of the window surface is below 51 degrees then you will have condensation - so now we talk a little more specifically about windows.

The interior surface temperature of a single lite of glass, when the temperature outside is 0 degrees F and the inside air temperature is 70 degrees, will be about 16 degrees. 

Add a storm window on the outside and the surface temperature of the inside lite jumps up to about 43 degrees – a huge improvement.

But these are center-of-glass readings and not the temperature readings at the edge of the window where condensation usually forms. A typical clear glass dual pane window is going to have center-of-glass temperature reading pretty much the same as a single pane with a storm – however, if that dual pane has a LowE coating and an argon gas infill then the center-of-glass temperature will be about 57 degrees – a 14 degree improvement over a clear glass dual pane or a single pane with storm window – but again, and more importantly, there will be a comparable edge of glass improvement as well, particularly if the IGU (Insulating Glass Unit) was manufactured using a warm edge spacer system. Also, the dual pane is going to have desiccant between the glass layers. Desiccant absorbs moisture keeping the inside of the dual pane system very dry. 

So what does a window temperature of 57 degrees mean? Well, as I mentioned earlier a home kept at 70 degrees with a 60% relative humidity has a dew point temperature of 51 degrees so it is much less likely that there will be condensation problem on those particular windows than there would be with a less energy efficient window - despite the relatively high relative humidity in the home. 

But, there is always a "but"…

Again, that 57 degree glass temperature is still a center-of-glass reading and the edge of glass temperature will be lower - actual temperature is dependent on both the spacer system used in the IG unit construction and on the material used to construct the sash. So even with a "57 degree" center-of-glass temperature it is still possible to get window condensation if there is enough moisture in the air. 

And consider that the interior glass temperatures are based on the fact that moving, warmer, indoor air is actually in contact with the glass at a given time. Curtains, shades, other obstructions can cause problems by blocking airflow across the glass – airflow that can have a huge effect on the condition of the window relating to condensation. Also, bay and bow windows can be more prone to condensation – again because of the possibility of decreased airflow over the glass. 

And finally, what can happen to the dew point if you keep your home at 70 degrees and you have a 65% relative humidity? Well, for one thing the dew point has jumped up to 57 degrees which we have already noted is the same as the window temperature. For another thing, anyone with 65% relative humidity in a home at 70 degrees has way too much moisture in their air and they are in serious need of some sort of ventilation system – or at least several good exhaust fans!


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## troubleseeker (Sep 25, 2006)

Kingfisher said:


> If as a "pro" you don't know that single pane windows sweat, you should really change jobs:laughing:


OK. Is that a request that I take some time off and work with you as a reading tutor?:laughing: He said that they were double pane, just that they did not have any type of gas between the panes.


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## Kingfisher (Nov 19, 2007)

While I could use the help, he never said they were "double paned" He said "they are the plain jane no argon gas type" I _assumed_ they were single. I may have been wrong, he never has stated. Many people assume single pane when someone refers to non lowE windows and does not know a lot about windows. He does not as he is running a huimidfier and wounder why the windoes are sweating. Thanks for the offer though


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## Ron6519 (Mar 28, 2007)

There's too much humidity in the house. Turn off the humidifier. Get an instrument to measure the humidity(hygrometer) and see at what level the windows stop sweating. Then turn on the humidifier and keep it below the level where water condenses on the glass.
If the humidifier is off for a week and you still have condensation, there's another problem contributing to the moisture.
I live in LI,NY and I have both double paned low-e Andersens and 1949 single paned double hungs with storms and don't have condensation. Relative humidity is 43% in the house.
Ron


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