Double-Hung Insert Renewal Andersen Windows in Minnesota

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Double-Hung Insert Renewal Andersen Windows in Minnesota

#1 Post by Ann » Wed Oct 13, 2010 1:55 pm

In May 2003, we replaced 11 energy-inefficient windows with windows installed by Andersen Renewal. These windows were inserts, not full frame window replacements. The choice was based on cost and the aluminum wrapped around the window sill (house built in 1994) was in excellent shape.

Pros: (1) The house feels warmer in the cold Minnesota winters & cooler in the summers. (2) The screens sit snug against the frame (unlike Marvin Window's) due to the track on top and latches (versus pins) on the side, keeping all bugs outside where they belong. (3) The wood veneer over the Fibrex material along with removable interior wood grills looks beautiful.

Cons: (1) Minor issue with the caulk around the exterior perimeter of the window which collects dirt, shows visible outline of dirt viewed from the street, and is difficult to clean. (2) Some of the windows require a greater level of effort to open the sash. (3) Condensation forms on the lower edges of the glass on both upper and lower sashes causing mold and darkening wood. (4) In the winter, condensation freezes between the bottom of the lower sash and the sill.

The condensation and formation of ice is both an inconvenience and safety hazard. During the winter we decrease the humidity to unbearable low levels. We installed an air exchanger to further remove humidity from our tightly sealed house and to restrict air forced through the cracks around the windows due to differences in air pressure. Condensation and ice has decreased, but it is still present. Every winter morning, I wipe away the condensation and open each window to break the ice build-up. I am very concerned that this is a safety hazard in the event of a fire and the need for my children to escape via their window. Andersen Renewal has attempted to fix the problem with caulk, expanding foam and weatherstripping. Condensation and ice still recurrs. I now need to replace more inefficient windows in my house, but I don't know what to do!!!! HELP!

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Windows on Washington
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Re: Double-Hung Insert Renewal Andersen Windows in Minnesota

#2 Post by Windows on Washington » Thu Oct 14, 2010 8:20 am


You obviously understand the concept as you have tried to address the humidity in the home.

The issue is that there is air leakage at the connection between the sill and the lower rail of the lower sash. If they have not replaced that weatherstripping at the connection between the two, that is the first thing I would do. You are getting cold exterior air that is flowing in at a very uncontrolled rate and contacting the warmer moist air in the home....result = condensation and wet windows.

This would be an instance where a window that has a poor air infiltration issue at the sill is the reason for your problem.

You can do several things here.

1. Make sure that weatherstripping seal is intact and has some compression and rebound (elasticity) left in it.
2. Make sure that there is not a heating register pointed at the window.
3. Increase air circulation around the window to keep the air moving.
4. Call Andersen corporate and ask for new windows or credit.
5. Put up some thermal shades to keep that warmer, higher Relative humidity air from reaching the windows.

Here is a quick breakdown of one of our resident experts about condensation...

-------------Window condensation --------------by Oberon

The reason why there is condensation on the interior of your windows has a really simple explanation – 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, the reason that the window surface temperature is below the dew point temperature can potentially become somewhat more complex, but I am going to offer a few thoughts and 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. Basically, 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 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…and I bet that that statement is a bit of a surprise to some folks…it is true however.

There are two ways to lower relative humidity – increase air temperature or decrease moisture content. If you increase the air temperature 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.

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.

The advantage? If it gets cold enough outside, the temperature in the airspace between the lites can get very low. By keeping that space dry, it helps to keep the dew point temperature very low as well; something not always possible when using a single pane and storm window.

Although a single pane with a good and tight storm window can help the interior lite to avoid condensation (when compared with a single lite and no storm), the storm window itself will frost up when the temperature is low enough – at a temperature usually well above the temperature that will cause the dual pane to ice up. It is unavoidable given the right circumstances
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 unlikely that there will be condensation problem on those particular windows despite the relatively high relative humidity in the home.

But what happens 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!

Somewhere back in this post I mentioned that lowering the relative humidity in your home may not help control condensation…that is still true…IF the relative humidity is lowered because of an increase in temperature. But, lowering the relative humidity by removing water is a different story because in that case you will also be lowering the dew point as you lower the relative humidity and that WILL help to control condensation on your windows.

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