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new double panes fogging outside.

Posted by island (My Page) on
Thu, Feb 17, 11 at 13:43

Just got new double pane replacement windows from Home Depot. It rained lightly last night and this morning 3 of them were fogged and were still that way when I left for work almost 2 hours later. One fogged completely, a perfect rectangle of fog surrounded by about 2" of unfogged window all around the perimiter.Weird. 2 others fogged along the bottom with that same 2" of unfogged area.
We had 12 windows redone and I should clarify we have sliding windows and it's only the non-sliding side of the 3 that fogged. The sliding sides with the screens are not fogged. All are in the same room and so far these are the only ones replaced on that side of the house which is typically the side that the rain falls towards the windows, but rain is usually light as it was last night.

I think they're fogged on the outside rather than between, but the 25 year old double panes I had before this never fogged. I live in San Diego so it's not like it's freezing outside and very warm inside and besides, I wouldn't think that should happen anyway with energy rated double panes?? Maybe by the time I get home from work they will unfog, but still don't think that's normal and how annoying to not be able to see clearly out new windows!

So before I call Home depot can someone please advise me if it is normal or not and why they're doing this?
Thank you!


Follow-Up Postings:

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RE: new double panes fogging outside.

Im guessing this is the east facing side of your house and the problem is early in the morning. If the fogging or condensation is on the exterior of the outer pane, this is normal and indicates your windows are operating normally. The reason this happens is because the glass get much cooler at night on the new windows than with the old because the heat is not transferring from inside your house to the outside as readily. When the sun comes up the warm rays hit the cooler glass causing it to warm up quickly and the surrounding air reaches it dew point causing moisture in the air to accumulate on the glass. It should dissapate within an hour or so as the glass warms up. This will occur occasionally at different times of the year when you have cooler nights and warmer days. Usually in the Spring and Fall. Again, it indicates your windows are working correctly.


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RE: new double panes fogging outside.

+1 skydawggy

absolutely normal, no cause for concern at all


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RE: new double panes fogging outside.

I noticed the same thing after I got new windows and panicked but then saw it was on the outside, not between the panes. As the others here say, it is normal. Low-E coatings can make it worse: http://www.rlcengineering.com/win_cond.htm
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.


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RE: new double panes fogging outside.

Thank you all for the info, explaination, and website.

As you can see from my post I thought just the opposite: the temp diff between 2 panes of well insulated low E glass seperated by a layer of gas, air, whatever it is, wouldn't register. I get it now.

I ended up putting a call in to Home Depot before these responses, (dying to know) and the project manager told me he called the company and both agreed it's normal, but a little unusual here because of our mild climate. Also we have our thermostat set back to 60 degrees at night and I noticed the fogging before the heat kicked in so again, unusual.

Project manager added he's had a few customers call with the same question. Most had it happen a couple of times when first installed and then the fogging never happened again and a few had it repeatedly happen and they replaced the glass with no further problems. So we'll see what happens. Happy to know it's supposedly normal, but if reoccurs with little temp change or only rain they will replace. Hope that isn't necessary!

Thanks again!


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RE: new double panes fogging outside.

What would they replace it with? The only thing that would prevent it from re-ocuring would be less efficient glass.


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RE: new double panes fogging outside.

I'm a little confused by that too. Saying it's normal, but also saying others have only had fogging occur a couple of times when first installed and others had it repeatedly occuring and resolved when replaced with new window of the same is a bit of a condradiction. What was odd was the perfect symmetry of the fogged area, like a smaller perfectly cut frosted glass was layed over the center. Also odd that last night it poured rain was much cooler out and warmer in and no fogging. Beats me.


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RE: new double panes fogging outside.

I have the same problem with my newly installed dual pane windows. It occurs mainly on all my west facing windows. I panicked when I saw this too and called the company who installed them. He had me speak with the sales rep in the area, who told me it was normal. I believe they should warn people about this. It is rather annoying not being able to see out any windows in the morning. It last for several hours too. I did not have this in my last house, but those windows were installed when the house was built and were not retrofit windows. They also were not low e. So, the low e might be the main problem.


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RE: new double panes fogging outside.

Fogging on the outside of the glass is normal and actually means the window is working well by preventing the heat from the home from transferring to the outside surface.

Colder outside surface = dewpoint.


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RE: new double panes fogging outside.

WoW +1


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RE: new double panes fogging outside.

This will become more of a problem as triple pane windows become more popular. There are some folks entertaining putting a low- or mid-emmissivity coating on the outside surface to prevent (since this would prevent the glass from signicant radiant cooling that causes it to drop below the dew point). (I need a coating like this on my car windshields!).


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RE: new double panes fogging outside.

  • Posted by oberon north central (My Page) on
    Fri, Mar 7, 14 at 17:00

Cardinal's new X89 coating was developed specifically for that application.

Like NEAT it is an "easy clean" surface 1 coating but with the intended added benefit of eliminating surface 1 condensation - basically morning or evening dew.

I wish I had it on my windshield as well!!

This post was edited by oberon on Fri, Mar 7, 14 at 17:01


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RE: new double panes fogging outside.

What...you don't like ice scraping in the AM Oberon?

Try not to live in the tundra and see if that helps!!!

Ha! I am going to call you Ober-Popsicle from now on.


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RE: new double panes fogging outside.

Two weeks ago my daughter is reading the forecast for the next week (actually last week) and she says "oh good, it's going to be above zero all next week, well except for in the morning when we go to work, it will still be below zero then".

Somehow at the time that still seemed like a positive forecast.

Yep, I am tired of scraping my windshield! I think we have well passed 50 days total below zero this winter and we have hit -20 or colder maybe 7 or 8 times. Not to mention the five or six feet of snow.

You know it's a real winter when you go outside wearing a sweatshirt (no hat or gloves) and you think "not bad at all kinda nice out", then you look and it's eight below zero.

For our Canadian and Euro friends, hat would be F and not C.

Kinda reminds me of winter when I was kid...and if you are bringing popscicles, I like root beer!


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