Major condensation inside with new Marvin windows in new house

threeapplesNovember 24, 2013

We have so much condensation with the interior of the sashes of our high end Marvin windows that I'm sure the wood will rot if I don't wipe them daily. It is mostly the upper sashes, with one exception, and is present on almost every window in our house (and we have a ton of windows). How much us normal and what do I do? Thanks

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What is your interior humidity level?

    Bookmark   November 24, 2013 at 1:01PM
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More often than not you house has too much humidity inside and the windows re were it shows up. As Jerry asked what is the humidity inside your home?

    Bookmark   November 24, 2013 at 1:10PM
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45%. We were told to keep it at this level so woodwork doesn't crack.

    Bookmark   November 24, 2013 at 1:41PM
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We usually keep it below 30 in the cold part of the winter and move it up in the spring to about that level.

    Bookmark   November 24, 2013 at 4:25PM
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To be fair, interior condensation is usually the result of high levels of humidity on the inside of your home. Inefficient windows will make it worse dont get me wrong.

    Bookmark   November 24, 2013 at 5:05PM
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Actually, windows that are doing their job will make the issue more visible to you by collecting that excess moisture to the surface of the glass. Almost like a magnet. That is what you are seeing.

    Bookmark   November 24, 2013 at 8:05PM
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Water condenses on the windows when the temperature of the glass drops below the dew point of the air. If you look at the owners manual of your humidifier, it will state recommended settings vs outside temperature. The chart shows typical settings. Keep in mind also that digital controls on humidifiers can vary by as much as +/- 10%.

    Bookmark   November 24, 2013 at 8:16PM
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You really should not have to keep your rh below 45% with new windows. If you still experience problems, you either have a poor installation that keeps the product from operating optimally, or you chose a product that does not offer very good thermal performance. That latter opinion may not be popular and I have to agree that Marvin generally makes a nice piece, but there are thermally superior choices available with better condensation resistance ratings. Most wood windows leak air like a sieve, so that would be a contributing factor as well.

    Bookmark   November 24, 2013 at 9:54PM
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I would encourage you to read published material regarding condensation that cover the industries stance on the issue and not just Marvin`s. Try GANA,, or BBB. They will explain interior air flow in the home and other contributing factors.

    Bookmark   November 25, 2013 at 4:03AM
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Windows on Washington Ltd

+1 to the other suggestions here.

I would reduce my rH levels to start with.

Next, have the windows checked for properness of installation and look for misalignment at the meeting rail and weatherstripping interfaces.

If the windows are hung right, you can get excess leakage at those areas and get condensation, regardless of the efficiency of the glass/frame/etc., if you have outside air infiltration.

Lastly, make sure the blinds, drapes, and window coverings at the window are open and allowing air to circulate at the window.

    Bookmark   November 25, 2013 at 7:03AM
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Thanks for all the good advice. We had a senior Marvin rep here last week and went through each window. If there were any issues he would have caught them.

I'll read up on the literature and bring this up to my builder.


    Bookmark   November 25, 2013 at 8:11AM
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High humidity in the house can lead to other problems that will not be as apparent as what you see on the windows. You will have moisture that makes it past your vapor barriers your exterior walls and condense on the interior side of your wall sheathing. Keeping the RH lower reduces this. I have a LOT of wood in our house. As the seasons change you can hear it pop. I keep the RH set at 35%, we are in Georgia so the exterior temperature is rarely cold enough to cause condensation. The accuracy of the controls on your humidifier should not be overestimated. Most people laugh at this, but the only way to really check the dew point and Relative humidity is using this method: In a small light weight thin walled container, (preferably metal like a mixing bowl) filled with water, add ice while stirring with a thermometer. The instant water forms on the outside of the container, note the temperature on the thermometer. This is your dew point. Then use the attached chart to determine Relative Humidity (assuming you are fairly close to sea level), you can then check this against your humidifier control. You can also use Sling psychrometers, but they are not that accurate, battery powered psychrometers are ok and old fashioned calibrated camel hair analogue gauges are good if you can find one.

    Bookmark   November 25, 2013 at 12:41PM
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I would to offer a solution to your dilemma. If you try you will see the answer.
A rh of 45 % is a GOOD THING !!!! An acrylic window add on to your present window will fix everything. We test the acrylics to minus 75 F with dry ice and achieve an R 6.5 . Bear in mind the best 3 pane windows with dual 1 / 2 inch spacers and low E with argon and krypton gas.
Contact us and we can ask you some questions about your interior environment to give you the best path to follow
1 807 627 4631

    Bookmark   November 27, 2013 at 11:57PM
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Windows on Washington Ltd

I am sorry sir, but that is incorrect.

As a previous poster mentioned, regardless of the condensation potential on the windows at the higher rH levels, too much humidity can create a host of other issues in the home beyond the visible demonstration of the the windows sweating.

Nothing about an interior storm does anything to address that either.

Many interior storms that I see also exacerbate the issue by limiting the drying and air circulation at the window surface.

Your advice is flawed on so many different levels that I felt it needed address.

Happy Thanksgiving.

    Bookmark   November 28, 2013 at 9:44AM
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+1 WoW

and a Happy Thanksgiving to all!!

    Bookmark   November 28, 2013 at 11:09AM
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Windowsonwashington , I know that you are basing your comment about interior storm windows on the what you have seen . What we propose is something you have not seen. A PROPER install of these will magnetically seal 100 % of the inside damp air from touching the cold glass. no air = no sweating

    Bookmark   November 28, 2013 at 11:20AM
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Windows on Washington Ltd


I know exactly what you are proposing and the fact of the matter is they do not work in this case and your recommendations of 45% rH is completely incorrect as well unless you want the client to rot their house from the inside out in a colder area of the country.

Humidity and interior moisture is one of the bigger issues out there in a cold climate and magnetically attached interior panels are not what most people determine to be aesthetically pleasing or even and option.

Your claims or R-Value are completely inaccurate as well.

It is safe to assume that a double pane wood window with Low-e/argon is going to be about a U-Factor of 0.30 or R-Value of 3.33.

Are you trying to tell me that adding an acrylic panel, even perfectly sealed, is going to nearly double that number?

When a trapped air space (completely static) is R-1.0, you are telling me that a layer of acrylic with no coating on it adds R-2.5?

I am sorry but that is not going to happen and you can claim whatever you want to in this case but science and facts do not support your claim.

    Bookmark   November 28, 2013 at 1:28PM
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I live in North Dakota, so too much humidity in the house is quickly evident with condensation on the windows. We had 3 large aquariums, and no exhaust fans in the bathrooms (we don't open the windows in the dead of winter). Excess humidity was definitely an issue - and in February, 45% was WAY too much!

Three years ago, we installed exhaust fans in the bathroom, got rid of the largest aquarium, and even run a dehumidifier in the winter. It has made a world of difference in the amount of condensation on the windows - and as others have said, it's the moisture issues you can't see that are a far more serious problem.

Seeing water vapor on the windows is a good thing - it alerts us to a potential moisture problem.

    Bookmark   December 2, 2013 at 7:40PM
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Don't have much to add other than that your first course of action should be to reduce that RH. If you still have issues, call the marvin rep back out. Often times things can be overlooked until they are identified as a complaint. You definitely DO want to get this addressed one way or the other as water + wood windows = bad news.

    Bookmark   December 3, 2013 at 12:04PM
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