Condensation on windows

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swimmer_spe

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Windows are double pane, about 15 years old. Humidity in the house is about 40%. It is winter.
Condensation is on most of the windows.

Why would this happen? It happened last winter, and the house was over 80%, so I bought a dehumidifyer.
 

Guzzle

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Assuming 70F indoor temp, this
says your glass is at 45F or below.

How cold is it outside?
 

swimmer_spe

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Assuming 70F indoor temp, this
says your glass is at 45F or below.

How cold is it outside?
House is ste at 22.5C and the outside temperature is about -5C
 

Guzzle

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The inert gas may have leaked out of your windows.
We try to get >50% RH in winter & our 10 YO windows never have condensation but we don't get 23F very often.
 

swimmer_spe

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The inert gas may have leaked out of your windows.
We try to get >50% RH in winter & our 10 YO windows never have condensation but we don't get 23F very often.
I am in Canada and we will get a week where it is below -40 for a week.
 

Guzzle

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And -40C = -40F.

I can't imagine your insulation requirements.
We live on the edge of what's classified as subtropical, with winter seldom reaching +14F.
 

swimmer_spe

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And -40C = -40F.

I can't imagine your insulation requirements.
We live on the edge of what's classified as subtropical, with winter seldom reaching +14F.
You caught that I didn't specify, or needed to.

New homes are 2x6 construction with spray foam filling the walls. We hit your low right now.
 

Guzzle

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I'd ask at least three of your neighbors whose houses were built when yours was [sample size > or = 3]. . .

Do they have this problem & when does it happen?

If they don't,
What is their relative humidity & inside temperature [you all share the same outside conditions]?

Plus ask anything else they can tell you about HVAC stuff.
It may be that every single thing on the issue of condensation or lack of it that
they tell you
may turn out to be relevant
in some way.

Cast a wide net.
 
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papakevin

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We purchased a home out in the woods and had terrible humidity issues. Turned out the HVAC super expensive filter was dirty, which created humidity issues inside the house. Crazy I know. Doubt this is your issue, but worth checking.
 

swimmer_spe

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We purchased a home out in the woods and had terrible humidity issues. Turned out the HVAC super expensive filter was dirty, which created humidity issues inside the house. Crazy I know. Doubt this is your issue, but worth checking.
Can't hurt to have a clean filter.
 

Steve123

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Condensation is on most of the windows.
Why would this happen?
What is the U value of your windows ?

If you are someplace that gets -40 for a week at a time, you really should have high performance windows.
Just the term "double pane" is meaningless. I don't think you can even buy single pane windows any more in Canada - would not be allowed on a new build anyways.
There are countless ways to configure window glass assemblies. All the manufacturers have many, many options. Types of gas in the fill and type of coatings all matter. Some coatings give better insulation values but not so good for condensation resistance. Manufacturers will also have a CR (condensation resistance) number for each type of glass assembly. Condensation resistance of triple pane windows is typically significantly better than double pane windows.

If the seal on the glass unit fails, you will get humid house air between the glass and then permanently cloudy windows all winter. When this happens, you know it, so I doubt that is your problem

But to answer your question - the humidity in your house is too high for the temperature of the glass. The humidity in one's house is typically pretty high going into a winter and it takes a while for it to drop. Probably you will see less condensation in January/February. And when it get real cold, you will see condensation regardless of how good your windows are.
 

Guzzle

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Heat tape for windows, like vehicle rear window heat tape, may help but I doubt anybody makes such a product. :(
 
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