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Excessive Frost on Windows


Asked by Ali Good
Posted Apr 25, 2010 8:15 PM ET
Edited Dec 12, 2011 2:06 AM ET


24 Answers

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Get out of the contract. You got a lemon.

Answered by Riversong
Posted Apr 25, 2010 8:36 PM ET


Window installation details are unlikely to be a factor. There are only two factors affecting condensation on window panes:

1. The temperature of the glass.

2. The indoor relative humidity.

If you are tired of looking at condensation on your windows, you have two choices:

1. Lower your indoor humidity by increasing your ventilation rate (or controlling the sources of high humidity).

2. Raise the temperature of your window glass. This can be done by adding exterior storms or by replacing double-glazed windows with new triple-glazed windows.

Don't forget — closing curtains at night is counterproductive if you want to reduce window condensation.

Answered by Martin Holladay
Posted Apr 26, 2010 8:04 AM ET


I would say that window installation and airtightness of windows CAN be a contributing factor.
Air leakage and thermal bridging near a window from poor installation can cause the microclimate near the window and the glass/window frame to be much cooler.
One of the windows seemed to be a slider which has poor airtightness to begin with.

Answered by John Brooks
Posted Apr 26, 2010 10:39 AM ET


Jobs like this are what give our profession a black eye!!! Horrible window and batt insulation installation, no thermal bypass mitigation, holes everywhere, etc. etc. Can I use your pictures for a ppt presentation on “What not to do when building a house”?
Your fan’s damper is flopping, probably because the home is negative pressured and a ton of air is coming-in thru the fan’s duct system.
Your fireplace is burning the sheathing because is improperly installed, no metal flashing and fire rated caulking. I hoep is a sealed combustion unit, otherwise you're probably backdrafting carbon monoxide.
Google: “Energy Star Thermal Bypass Guide”, download the 86 page document and you will have an answer for every question you have.

Answered by Armando Cobo
Posted Apr 26, 2010 12:21 PM ET



Do you know the standard recommendations by Canadian Health for healthy living is 30-40%. II disagree with your comment. The relative humidiy as ,measured by a hygrometer at various places is below health standards. Something is wrong with the circulation in the home.

Answered by Wes
Posted Apr 26, 2010 3:56 PM ET


Armand, you have my permission to use the pictures in your presentation.

Answered by Wes
Posted Apr 26, 2010 4:29 PM ET


You can disagree with my comment all you want, but it is a simple explanation of the physics involved.

It's not really a matter of opinion. Railing against physics is like railing against gravity.

Physics offers you two choices. If you are satisfied with your indoor humidity levels, your only option is to raise the temperature of your window glass. That means storm windows or triple glazing.

Answered by Martin Holladay
Posted Apr 26, 2010 5:47 PM ET


No, it's not a matter of opinion or physics, but of misinterpretation.

The indoor RH shown on the digital hygrometer is 29% at 72°. That is low enough to prevent condensation on all but single-glazed windows at normal winter temperatures.

There is substantial frost on the glass, the window sash and the crank handle. This is due to major air leakage, which could be from poor quality windows or poor quality installation or both.

Answered by Riversong
Posted Apr 26, 2010 6:31 PM ET


Robert and Wes,
29% RH at 72 degrees may be low enough to prevent condensation on dual-glazed windows at "normal" winter temperatures, but are Edmonton's winter temps normal?
There appears to be over 10,000 HDDs in Edmonton Canada (Edmontonians correct me if I am wrong) I would say that is NOT normal.
It definitely looks like garbage, leaky windows were installed, but I think you may get condensation on dual-glazed windows in this type of climate when RH levels are +30%.

Answered by Brett Moyer
Posted Apr 26, 2010 8:35 PM ET


Brett: I guess the NATIONAL BUILDING CODE IS WRONG. Did you look at my thermal images. Here is an excerpt from the NATIONAL BUILDING CODE which
The following articles of the 1997 Alberra Building Code states as follows; Thermally insulatedwall, ceiling andfloor assemblies shall be constructed so as
to include an air barrier system which will provide a continuous bcrrier to air leaknge
a) from the interior of the building into wall, floor, attic or roof spaces, sufficient to
prevent excessive moisture condensation in such spaces during the winter, and
b) from the exterior inward sfficient to prevent moisture condensation on the room side
during winter and to ensure comfortable conditions for the occupants.

Answered by Wes
Posted Apr 26, 2010 8:53 PM ET


BRETT: I appreciate both of your opinions.
. I actually think it is a combination of both the windows and the insulation since the rest of my house was poorly done. The key with this is to prevent excessive moisture condensation. Physics is used in both theories.

At the end of the day, I need a remedy. The builder is running from the issue. The warranty company is a joke.

Thanks for the feedback. The windows are actually used in a lot of places in Edmonton without the same issue as I am experiencing which I believe is the result of the framer's shoddy workmanship with poor insulaiton around the windows. I agree that triple pane windows are best, however the windows in my home are highly rated.

Answered by Wes
Posted Apr 26, 2010 9:05 PM ET



You should either sue the builder or just abandon the house and let the bank repossess it.

Answered by Riversong
Posted Apr 26, 2010 9:24 PM ET


Looks like Wes is the latest subject in an experiment that is essentially a race to the bottom.

Before I get rolling, let me remind people that Wes lives in a really, really cold climate. About 10,000 HDD on the Fahrenheit scale. When it's unremittingly cold and the days are short, overnight frost doesn't melt during the day - it just accumulates day after day after day.

Determining if the problem is installation is fairly easy. Remove the trim and look. Ideally the windows should be foamed in place and the foam should extend out under the window. If they aren't insulated in this manner insulate say the left half of several windows and see if this has an effect.

Having said that, my informed guess is that very little , if any, of the frost in the pictures is due to installation. The clearest exception would be #12 where there is frost on the jamb extension.

Most of the frost is, in my view, is due the frame design as opposed to installation or even air leakage. The frost is unfortunately typical of a builder window in frigidly cold weather and higher than average humidities.

Vinyl window frames used to be complicated honeycombs of smaller chambers. In an effort to reduce costs many suppliers are eliminating internal walls, profiles are becoming more open, as chambers are combined. Just as natural convection between the panes of an insulated glass unit make it coldest along its bottom edge so too will open vertical tubes be coldest at their base. Good examples of this are the jambs in pictures #2, #16 and #17.

For the record any open tube; vinyl, aluminum or fiberglass, can suffer from this. Insulated frames work because they not only suppress conduction, but also suppress convection.

The slider in #4 also exhibits a classic cold weather frost pattern that is often also seen on sliding doors. The outer interlock stile (the vertical member of the outer sash that isn't in the frame's jamb) is cold on 2 sides – its outside face and its end. The glass in the outer sash is not just cold on its bottom, but also on its exposed side.


Aside from Martin's suggestions, one simple trick to make outswing windows warmer is to remove the screen.

Also, if you're using a setback thermostat, be less aggressive on the setback. While setback thermostats usually decrease energy bills, they can also increase realtive humidity. If you decrease air temperature, and the absolute amount of moisture in the air remains constant the relative humidity – relative to what the air can hold at the lower temperature - will rise. Even worse while the furnace doesn't run for for the first part of the setback cycle, closed off bedrooms drop below the setback setting, becoming even colder, encouraging even more frost. The worst condensation problems i've seen are always in houses with aggressive setback thermostat settings.


The ultimate remedy is of course avoiding worst of the problem with a better window. Triple glazing has more condensation resistance than double glazing. Insulating spacers produce warmer edges than metal spacers. Insulated polymer frames and sashes suppress intraframe convection. (Wood frames,of course, are also free from the effects of internal convection.) Windows set deeper into the rough opening are more readily warmer by the room than those at the exterior face of deep wall.

While you can heat trace hollow alumuinum frames and even heat glass, ultimately no conventional window is condensation-proof or even frost-proof. Not that excuses what's in Wes' home.........

Answered by Stephen Thwaites
Posted Apr 26, 2010 11:06 PM ET


By NO means am I defending the builder. Looking through the photographs on the website you provided, one can assess that the builder either didn't know what he/she was doing, or maliciously cut corners to save money.
Either way, I agree with Robert... sue the builder, or walk (no RUN) away from the home.
If running is not an option, you have the appropriate documentation for legal action. With the photos on your website, accompanied by the testimony of a local building expert, you have a solid case.
Good luck.

Answered by Brett Moyer
Posted Apr 26, 2010 11:08 PM ET


While Edmonton may have a 10,000 HDD climate, the winter low temperature is only 0°F. It gets much colder here in northern Vermont and I don't get that much frost on my single-glazed wooden windows.

Answered by Riversong
Posted Apr 27, 2010 8:34 PM ET


My mother had sliding windows which were 30 years old and no frost or even condensation on the windows. . I am 43 years old in this city and have not seen this before in this climate so I think I can make a comment on this. This is excessive. .

Answered by Wes
Posted Apr 27, 2010 9:57 PM ET


An update. It was determined by an Engineering company that the windows did not have sufficient insulation and/or seal at the window. We have since had this repared. We also have had similar winter conditions with similar humidity as measured by the same hygrometer inside the home. The problem has went away. So the issue has been fixed. I hope this enlightens those that have given their opinion on the mattter and that there is a micro-climate at the windows.

Answered by Wes
Posted Dec 22, 2010 12:19 AM ET


Thanks for the feedback.

Answered by John Brooks
Posted Dec 22, 2010 7:06 AM ET
Edited Dec 22, 2010 10:34 AM ET.


Hi Wes,
Can you describe in more detail how your window issue was fixed?
Was it the airtightness and insulation of the "Installation" that was corrected?
Or was it a problem with the window unit that was corrected.

Someone at another forum is reporting a similar problem.

My thinking is that you are talking about correcting the poor installation.
thank you

BTW the link to your photos is no longer valid...
you can now upload photos here if you like

Answered by John Brooks
Posted Jan 17, 2011 4:51 PM ET
Edited Jan 17, 2011 5:01 PM ET.


I, too, would be interested in hearing the details of this repair. And would like to revisit the pictures you had posted.

It was -3°F last night here and I had just a light touch of frost on my single-glazed wood-framed windows at 28%RH.

Answered by Riversong
Posted Jan 17, 2011 5:16 PM ET


Hi Guys:

Here is an excerpt from the code. Lived in Alberta my whole life with double glazed windows and extreme temperatures. No issues until brand new home built in the boom. Perhaps this will shed light on the issue. The problem was with not following manufactured recommendations for installation and not following MINIMUM building code requirements. You will note in the enclosed picture that you can see some insulation between the window and the framing. Also see thermal from outside where most heat is escaping where there was no insulation or seal. It was repaired with foam at the exterior and rest of cavity fileed with insulation.

Insulation Excerpt "Continuity of the thermal barrier is important primarily to reduce condensation potential on the interior glazing and interior finish surfaces, and also for energy considerations, interior comfort and thermal environment."

Source:Patenaude, A, Scott D. and M. Lux,(1988) "Integrating the Window with The Building Envleope", National Research Council of Canada, Retrieved June 25, 2010 from http://www.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/88-window-envelope.html

Answered by Ali Good
Posted Jan 17, 2011 7:19 PM ET
Edited Jan 18, 2011 1:42 AM ET.


The IR picture you attached indicates that most heat loss is through the frame. You may have fixed the air leakage problem around the window units, but those uninsulated vinyl frames are a poor choice for cold-climate installations.

Answered by Riversong
Posted Jan 17, 2011 7:30 PM ET


I may not be reading the thermal image right...?
It looks to me that the extra "hot" (conductive)part is the glass spacer
the vinyl frame is cool and the framing around the window is "warm"

Answered by John Brooks
Posted Jan 17, 2011 8:34 PM ET
Edited Jan 17, 2011 8:38 PM ET.


The thermal image is too small to read easily, but I agree that the sash is losing more heat than the glass. This is pretty typical of most windows I look at, and the vinyl is almost certainly not insulated.

The website the OP posted doesn't appear to have any pictures of a house... or is it just me?

Answered by David Meiland
Posted Jan 18, 2011 12:58 AM ET

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