New windows and steam/condensation?????

angeezNovember 26, 2012

Ok I have a ?. We just got Marvin Infinity windows put in our 2 bedrooms today. We live in a split foyer that is 1200 sq. ft. on the main level. The master bedroom has a doorway that goes into the main bath that is roughly 11 1/2 ft. x 7 1/4 ft. Tonight when giving the kids a bath and running the exhaust fan (Nautilus and have no idea how many CFM's) I noticed that at the bottom of the glass on our new windows in our bedroom was some fogginess/steam that I could wipe off. We replaced these windows due to supposed collapsed glass and the large amt. of condensation we get in the winter. WHY was there fogginess on the bottom of my window. THIS IRRITATES ME. Could my exhaust fan in the bathroom be to small???? I am going to be so upset if I get condensation on my new windows. ADVICE PLEASE!!! Hope this isn't too confusing!

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Where are you located and what was the outside temp? The situation that you describe is not at all uncommon. As glass temp goes down and the relative humidity in the room goes up, condensation can occur. The windows can be (and probably are) functioning as designed. Here is a cool little dew point calculator that I found.

Here is a link that might be useful: dew point calculator

    Bookmark   November 27, 2012 at 9:48AM
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Homesealed....I am in Central Iowa and the temp is around 15-18 degrees. I was able to figure out how many CFM's our bathroom exhaust fan is. It is a 70 CFM and our bathroom should have atleast 84-110 CFM's. Should I get a new one??? THANKS FOR YOU HELP!!!

    Bookmark   November 27, 2012 at 10:47AM
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How does the dew point calculator work? I am confused :)

    Bookmark   November 27, 2012 at 11:06AM
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You have condensation on your windows because the glass temperature is below the dew point.

Dew point temperature is the transition between evaporation and condensation. Dew point is defined as saturation vapor density, or actual humidity, or simply, 100% relative humidity. Go above the dew point temperature and you have evaporation, go below it and you have condensation.

Dew point is "fixed" depending on the moisture in the air. "X" moisture level will always equal "Y" dew point.

In other words, if the air in your home holds 5 grams moisture per cubic meter of air then the dew point will fall at 32 degrees F. Ten grams moisture per cubic meter and the dew point is at 52 degrees F. These numbers are totally independent of the temperature in your home, or the temperature outside, or any other temperature. Dew point is based on moisture level - period.

Most folks will refer to relative humidity when dealing with window moisture issues simply because we use RH all the time while we rarely ever consider actual humidity. Relative humidity is the actual vapor density divided by saturation vapor density - or - the percentage of moisture in the air versus the maximum amount of moisture that the air can hold at a specified temperature.

The really excellent calculator that Homesealed linked (I saved it in my favorites) allows you to adjust the the RH, temperature and dew point (again keep in mind that dew point is the temperature equivalent of the moisture in the air).

If we set the dew point at 32 degrees and then "solve for" RH, we can adjust the temperature slide up and down see what the RH would be at several given temperatures.
If we raise the dew point to 52 degrees, we have doubled the moisture level (as mentioned earlier) to 10 grams per cubic meter, and we can see the effect that change has on the RH at various temperatures.

If we set temperature at 72 degrees and the move the RH to 50% - what is the dew point temp?

So what does it all mean in your case? Basically, in order to stop condensation from forming on the surface of your windows you must:

lower the dew point by removing moisture from the air, or
warm up the window surface to a temperature above the dew point, or
do some combination of both.

So given a dew point of 32 degrees, if your glass temp is 32 degrees, then you are at 100% RH and dealing with condensation. Warm the surface to 40 degrees and you are at 75% RH with no condensation.
Given a dew point of 52 degrees, if the glass is at or below 52 degrees then you have condensation. Since it is quite possible that the glass temperature of your windows could be right around this temperature, then lowering the level of moisture in the air is probably going to be your best solution.

I think it's pretty much a given that the bath is putting a lot more moisture in the air than the exhaust fan is removing. A major gain of upgraded windows is that they tighter which helps to prevent air leakage to the outside. This is a good thing for keeping heat in, but it will also result in keeping moisture in as well. That excess moisture will raise the dew point in your home and can result in condensation that you never saw in the past.

Since you mentioned that you had condensation issues in the past, you might want to see just how much moisture that you do have inside your home. You might consider that if you are seeing extensive moisture on your windows, there may also be condensation inside your walls that you aren't seeing.

To help eliminate minor "misting" on your windows, use a fan to circulate warmer room air over the glass when bathing the kids, or at any time minor condensation becomes an issue. This should help to warm the glass to a level above the dew point.

Also, as Homesealed asked, what was the outside temperature? As it gets colder outside the glass in your windows will also get colder which will increase the possibility of condensation. As it gets colder outside it's almost always a good idea to lower the moisture level inside.

    Bookmark   November 27, 2012 at 11:45AM
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An excellent post by Oberon.

To answer your last question angeez, a new bath exaust fan may very well be in order and take care of the excessive moisture. It is also common to see installation issues with bath fans where ducting is crimped, baffle operation is inhibited by a screw securing the ducting, etc, etc. These issues will cause it to move even less air (and moisture). Ultimately, if you want to rule out the possibility of the windows being an issue, you can take a temperature of the glass (should be somewhere between 40-50* at the outside temp given), and also get a reading on the relative humidity in the home (more specifically in that room, and under the circumstances where your condensation occurs). If the glass temp comes in low and the RH is within acceptable levels, then perhaps the windows need attention, however given the circumstances I would say that is highly unlikely.

    Bookmark   November 27, 2012 at 12:37PM
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I just want to clarify that we did have very extensive condensation before but I assume that was due the the collapsed glass we had in our 1991 ANDERSON windows. This morning the condensation was a very small bead (1/8" or so)at the bottom of each window in the bathroom and our bedroom that is joined by a door as well as my sons room and the kitchen, all on the main floor. We just had the Infinity windows installed yesterday so I would highly doubt it is the windows, right? I also know that besides our low CFM exhaust fan that I don't believe goes outside, only to the attic, also no air exchange on our furnace or outside vent above our stove. How would I tell the glass temp?

    Bookmark   November 27, 2012 at 1:56PM
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You definitely want to get that fan ducting properly run to the exterior. You are inviting a host of issues by just exhausting it into the attic... By your description, it sounds like the windows are fine.

    Bookmark   November 27, 2012 at 5:08PM
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angeez do I know for sure if it is vented outside?

    Bookmark   November 27, 2012 at 6:40PM
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Windows on Washington

Get up in the attic or look for a penetration on the roof or through the side of the home.

All moisture control should always vent through the roof/side wall.

    Bookmark   November 28, 2012 at 8:08AM
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Yep... There should be a shroud either on the roof or the side of the house where it exhausts. If you are not sure, peeking in the attic would be best.

    Bookmark   November 28, 2012 at 1:49PM
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