Condensation on outside of my double pane windows

I read your page

about condensation in double pane windows.

About a year and half ago, I had some double pane windows installed and there was no condensation for some time. But then I began to notice a draft coming from the double pane windows at the front of my house and also to notice condensation on two of the windows. (There are three in from and only two of them show condensation).

Today, the installer came back and noted that the condensation was on the outside of the windows and not between the panes.

Is this normal? If so, why is it only affecting 2 of the windows?

Thanks for your help in this matter.

San Francisco, CA

Doug check to see if they are leaking where they come together Locks may need adjustment.

This page should help some…

Were the supplied windows supposed to have “Low Emissivity” coating on the glass and/or Argon gas-filled? If so, the unit not having condensation should be checked to see if there has been a miss on either/both of these items when assembling the unit.

The above answers are only speculative…

Summer condensation occurs when the outside window surface is cooler than the dew point temperature of the outside air. In the southeast US, summer dew point temperatures range from about 65F to 75F. When temperatures inside the building are within this range, summer condensation problems can occur.

The outside glass surface in energy efficient windows will be closer to the outside air temperature, while the outside glass of an in-efficient window will be closer to the inside temperature. Low-E coatings help reduce the amount of radiant heat transfer through a window. As the summer sun warms the outside glass, a Low-E coating reduces the amount of this heat that moves inward. (The outer glass can warm significantly in the sunshine. During the winter, the inside glass is warmer because of the reduced radiant heat movement outward, and you don’t get that “cold” feeling sitting next to a window.) At night during the summer, heat is radiated from the outside glass to the cold sky and other objects. The Low-E coating reduces the heat transfer from inside, so the outside glass surface can cool significantly below outside air temperatures.

In cases where the inside temperature is below the outside temperature, a Low-E coating will allow the outside glass temperature to drop to about the same as that of an inefficient window. In cases where the outside air is colder than the inside temperature, a Low-E coating allows the outside glass to get even colder. Therefore under the right conditions, windows with Low-E coatings can develop more summer condensation than inefficient windows.

Since we cannot control the outside dew point temperature (or relative humidity), the options for preventing summer window condensation problems are to warm the inside surface of the window as a way to warm the outside surface. Raising the thermostat setting is about the only option. Exterior shutters, shades or even trees can help reduce summer condensation problems as well.

In summary, condensation occurs when a surface falls below the dew point temperature of the air. The outside glass in an energy efficient window will be closer to the outside temperature, and the inside glass will be closer to the inside temperature. The glass in an inefficient window will be more heavily influenced by both inside and outside temperatures. A Low-E coating (that reduces radiant heat transfer) will tend to warm the inside surface in the winter, and the outside surface in summer sunshine. A Low-E coating will also lower the outside surface temperature at night in the summer. Therefore, a low-E coating will reduce the potential for winter condensation, while creating more potential for summer condensation situations (especially if the inside thermostat is set near or below the outside dew point temperature.)

Correct, and the right information.

From the initial poster:

"Today, the installer came back and noted that the condensation was on the outside of the windows and not between the panes.

Is this normal? If so, why is it only affecting 2 of the windows?"

We still haven’t answered the question or fully told SF how to analyze/test the thermopanes/sealed glass panes for argon/krypton gas loss, missed Low “E” coating, etc.

There are Argon/Krypton gas testers but they are very rare.

One way I used to verify Low “E” coatings is to hold a match or lighter flame close to an inside corner of the window sash and count reflections from the glass surfaces. A regular thermopane with no Low “E” will have 2 flame reflections while the pane with Low “E” will have 3 reflections.

I just had new windows installed and had the same concern. It is not uncommon in areas with high humidity to have condensation on the outside of the windows. this is due to the high insulating value of double pane, low-E glass with argon. the outside glass actually gets colder then the air allowing condensation to form. there is no way to control the humity on the outside of your home so there is no solution and nothing to worry about. the windows are working as designed.

The condensation is on the inside panes of all the main floor windows and patio door (NOT outside & NOT between the panes). I find it necessary to wipe off the water every morning.


Can we get this spam deleted?

I agree James. And how is it they can change the thread title on individual posts???

Thanks for the heads up, guys.

I just had two energy efficient windows installed yesterday and this morning had condensation on the outside of only these two windows.

Until I read the post from 1/1/2010, I was concerned, but this poster offered a thorough well
thought out explanation.

Thanks for keeping this thread available!!

Thank you for good explanation. I, too, just had windows installed and two of the four have outside condensation when colder and moister outside. I guess I will just wash windows more often :frowning:


Just in case this isn’t spam and somebody really wants to know, you can contact me.

What is posted follows theory, but is not actually what is happening here.
Until you can see it, you can’t understand it.

Probably the closest comparison we can come up with is if you ever notice that you can get frost on your car windows on one side and not the other? Not because the sun shining on one side, this occurs in the middle of the night. There is a reason for this. It’s quite simple actually but I’m not going to educate the window salesman here.

If you actually have a problem and you want it solved you can contact me.

Far as I know there is nothing complex about it.(explanation)

Warm air hold more moisture because heat expands the space in between molecules which gives it more storage space to hold moisture.

When this hits cooler air the space contracts and the moisture gets squeezed out.

How is that for simple ?
Why make it so hard that you need to be a physicist.

Excellent information. I am still not sure what is happening, but the statement that said the windows are functioning normally since the condensation is all on the outside of the window is all I needed to know. Thank you so much

8 years ago I replaced all the windows in the back of my house. in the previous 20 years I never had a condensation problem on any window. 3 years in, 1 window starts getting condensation. the next year its worse. then last year one of the larger windows, with two identical panes gets condensation on one pane but not the other. these two panes are 2 inches apart. Some replacement window companies tel me that this indicates the argon between the glass has leaked out of one pane and not the other. My neighbours on either side never have condensation on any of their windows.

So I would like all the experts I have read on this form on this forum to explain to me how this happens. Does the "environment wake up one morning and say I will pick this window today.

Look up “dew point”.

Use a hygrometer and determine the psychrometric properties of air.

Measure the glass temperature with your $32,000 thermal camera…

Or, accept Bob’s “cut and paste” from the NACHI CE Corse.

There is a thing called the “View Factor” that most thermal camera owners refuse to go to thermography school and learn about. It has to do with geometry.

This is how the environment picks which window today…