Window Condensation

By
©1993-2012 Tim Carter

        
Summary: Many homeowners experience window condensation in the winter. Condensation can form on windows, walls, ceilings, the underside of roofs, and more places. Condensation on windows comes from the water vapor inside your home. Homes that are sealed-up, so they are more energy efficient, can produce condensation on windows.

DEAR TIM: I have massive amounts of window condensation forming on expensive name-brand windows in my new home. My sister has condensation on some pricey vinyl-replacement windows. The window people say it is our fault stating that the humidity is too high in our homes. I even have condensation on a storm door. What is cure for condensation, and how can I stop the water damage and mold that is forming? Patty S.

DEAR PATTY: Window condensation plagues many a homeowner each winter. Condensation can form on windows, skylights, walls, ceilings, the underside of roofs, inside closets, etc. The source of condensation is invisible water vapor that is a component of the air inside your home. Condensation on windows, even new ones, has become an increasingly more-common problem because we are building new homes better and sealing up existing homes so they are more energy-efficient.

I have people ask me frequently what is condensation. Condensation is a physical process that happens when water changes from the gaseous state to the liquid state. The air we breath and that surrounds our planet holds vast amounts of water - billions of tons. Some of this water is invisible while much of it is liquid. You can see liquid water in the sky each time you look at a cloud.

This glass has condensation on it that can peel the paint and cause both wood rot and mold if it is not stopped!  PHOTO CREDIT: Tim Carter
This glass has condensation on it that can peel the paint and cause both wood rot and mold if it is not stopped! PHOTO CREDIT: Tim Carter
The water vapor turns to liquid water when it comes into contact with a cool or cold surface. For condensation to form, the temperature of the surface must be at or below the dew point of the air that is touching up against the cool surface. This dew point is a moving target, and this is why the window companies are saying you and your sister might be the cause of the window condensation.

A given volume of air can only hold so much water vapor at a given temperature. The warmer the air, the more water vapor it can hold. Certainly you have experienced stifling air in the summer months where the air seems so thick you can cut it. If you had an instrument to measure relative humidity with you, you would have discovered the dew point of that air might have been as high as 72 F. This means that if there was an object outdoors whose surface was 72 F or lower, you would see water droplets forming on that relatively warm surface!

The air inside your home or that of your sister might have a dew point of 50 F. This means that if the surface temperature of the glass drops to 50 F or below, you are going to see condensation.

Even though you and your sister have state-of-the-art windows that might have Low-E insulated glass with Argon or some other inert gas between the panes of glass, you can still get window condensation. Here is why. If you keep the temperature and humidity constant inside your home as many do, condensation will form on windows as the outside temperature plummets in bitter-cold weather. The temperature of the surface of the inside pane of glass is not constant as the outdoor temperature drops! Your furnace is fighting to keep the temperature up, but it will always lose that battle if it is sized properly for your home.

You can stop or minimize condensation by monitoring the amount of water vapor in your home. As the outdoor temperature drops you must lower the amount of water in you air. Modern humidifiers have controls with outdoor sensors that can do this automatically. You should also use exhaust fans in your kitchen and bathrooms that exhaust air outdoors, not into an attic space. Indoor plants, laundry that is drying indoors, interior painting, cooking, crawl spaces that have no vapor barriers, etc. all can aggravate window condensation.

Older homes had window-condensation issues, but they were not always as bad. The reason was simple. Old homes like the one I grew up in were often very drafty. The influx of cold air mixing with the interior air made the relative humidity of the air lower. Cold air is dry by nature, and when it is mixed with warm air, the humidity drops as does the dew point! This means you would not see condensation form in an old drafty house but might see it in a new home that could be built next door.

Condensation on a storm door is very common. Storm doors are installed to act as a water and wind barrier. They often have single-pane glass and the temperature of that glass is frequently equal to the actual outdoor temperature. Moist warmer air from inside your home leaks past your primary door and contacts the cold storm-door glass. Condensation starts to form in seconds if the storm door is sealed well as it should be.

Fans that blow air on window condensation can help evaporate the liquid water putting it back into the gaseous state. But always remember that the light fog you see in the first phase of window condensation is doing the same thing a blaring smoke detector does; it is screaming at you warning that you have too much water in your air.



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Comments:

Welcome! I, Tim Carter, don't answer questions here. If you post a question here in the Comments Area, perhaps another visitor will help you. You need to go to the Ask Tim page if you want a question answered. Once there, look closely at how many weeks behind we are. Please be patient as you use this free service. If you have an emergency and need to talk to me, there is an option there for you.
Joe Bartmann
20 Sep 2008, 23:07
Hello,

I am wondering if this site can help me get some badly needed information regarding window condensation. I need to conduct a survey to find out if homeowners know several things about the issue. I am in the construction business and need some market research done because I am planning on helping address this problem. I currently hold a provisional patent on some new technology to remedy most of these window condensation cases. If you would be interested in helping us (even for a fee) please contact me. My number is (920) 422-0739 or my email is joe.bartmann@sbcglobal.net Thank you in advance for your time and consideration regarding this issue.

Sincerely,
Joe Bartmann
Terry M. Johnson
28 Sep 2008, 18:17
We have installed a glass outdoor bullention board at our cemetery(grave directory)we are having trouble with condensation. The water causes mildew on the directory, can anything be done to prevent this from happening
Jessica
17 Oct 2008, 13:41
We have recently moved into an older home. It has new windows but plaster walls. The back bedrooms have a horrific amount of black mold on the walls under all the windows and the windows condence badly. We have attempted to lower the humidity in our home however it is to no avail. I have five small children, one of them an infant and two others are autistic and lick just about everything so this is a huge problem. is it safe to use kiltz to controll the wet or will this damage the plaster in the wall, if this is a solution at all.
sal
19 Nov 2008, 09:28
I would like to know why I get moisture only where the two double pane windows meet for about a inch or so . Is the gasket between the two windows shot or is this normal . My windows are probably 10 years old and my humidifier doesnt work
Paul
22 Nov 2008, 09:08
This summer we put insulation in our attic and blown in fiberglass in the knee wall of our 1850 farm house in maine. We never had condensation problems before and now all the windows in the house are soaked,even after wiping them down an hour later they're soaked again. Is a dehumidifier the answer?
Dee
25 Nov 2008, 09:16
We had single glazed windows in our 1970s house for 35 years and last year we installed new UPVC double glazed windows and doors all round the house. As this is the first winter with the double glazing we were really looking forward to a Wnter of no condensation as it used to be really bad. However, we still get some condensation on most of the windows.. just aroun the edges mainly for an inch or so and at the bottom, more at the fro of the house which is North Facing. We have the temperature of the house at 14/16 degrees C in the day and reduce it very slightly at nidht so that the heating kicks in if the temperature drops very low. Is this the best way to control the condensation? We have read notes on reducing the humidity in the house and will try this. Are there any localised appliances that can be placed on windowsills to help.
Jesse
27 Nov 2008, 19:01
Do air exchangers help with condensation on the windows?
Kim
03 Dec 2008, 17:34
install a wood stove and leave the window open all winter long to give fresh air intake to combust the wood....it's the only solution that I know of after living across the country (Canada) in probably two dozen different houses.
I've spent 15 minutes on this website and basically it seems there's a lot of explaining why it happens but no methods for reducing it!
NN
09 Dec 2008, 12:05
I was experiencing some severe window condensation. It got the point that the water was pouring onto my carpets and also damaging the paint by my windows and early mold signs were beginning to develop. I live in a new condo in WI, so it is freezing and snowy outside. Wiping down accomplished nothing as it would be wet an hour later. So what I did was I wiped all the windowsills and then just ever so slightly cracked each window open (hardly even noticeable to the eye). No noticeable temperature change in the room, but just enough to replicate a tiny air leak that an old window might have. They have been dry as a bone for 2 days. Crossing my fingers this will last!
CP
15 Dec 2008, 12:52
I too am experiencing window condensation on a brand new home built in 2006 and am in TX (and then only when the temperatures drop to about 34 F or below). The windows, most unfortunately, are aluminum framed, but, a very energy efficient home nevertheless. I have to wipe down the window sills, the tops of the bottom portion of the double hung windows (where the locks are), the lip of the windows and usually in the corners where the caulking is.

Will a dehumidifier solve this problem? Does it have to be a single unit in each room where we are having the problems or a housewide dehumidifier?

To the poster, NN on December 9, that tried cracking each window open: is this still working for you?

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