# How does double glazing REALLY work?



## CBGB (8 Nov 2011)

I know how the concept of air/gas filled double glazing works. But on a practical level can anyone answer the following:
1) if the windows are good should you NEVER get condensation on the inside of the house? If you get condensation are the windows just bad?
My folks fitted new double glazed argon filled windows. Now with the cold weather they are getting condenstion on the inside of the window. My mams obvious reaction is that "thats what use to happen with my single glazed!". When it is very cold outside the gas/air in the gap eventually cools down, giving you warm inside pane surface in contact with cold and condensation. Obviously the gas would take longer as it is inert. So is it inevitable that they will get condensation? 
2) Why, as I've read here somewhere, is condensation on the outside better than the inside? Is this not the same action as above, in that, after time the air/gas has warmed up and is now the same temperature as inside the house. So, the outside pane is warm and condensation occurs. At that point will the house not lose the heat (warm in contact with cold) in the same way the condensation on the inside would?
Or am I nuts?


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## Superman (8 Nov 2011)

Condensation happens when warm moisture laden air comes in contact with something cold.
Change one of those variables:
warm
moisture-laden
cold
and you don't get condensation.
Condensation on the outside of your building is not really your problem as such. It means that your outer surface of your house is colder than the outside.
If your house is warm on the inside and cold on the inside that means you've done a great job of keeping the heat in.

Double glazing works by making the "something cold" less cold - so less likely to get condensation.

You still have two variables to play with though - the warmth of the house and the moisture.
You can reduce the moisture by ventilating well, by making sure you don't air dry clothes/boil lots of water etc.
You can also reduce the overall heating of the house if it is too warm.


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## Billo (8 Nov 2011)

Did you do a google search for some answers e.g.

[broken link removed]


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## onq (8 Nov 2011)

Heating a surface above the dew point helps prevent condensation.
Radiant heat is better at this than warming the air, which transfers its heat poorly to objects.
Of course, closing the curtains means that most if any radiant heat will be absorbed before it reaches the inner pane of the windows 

http://en.wikipedia.org/wiki/Dew_point

Ventilating a space to reduce water vapour in the air below saturation helps prevent condensation.
Local ventilation near a source of water vapour is more efficient than general space ventilation - eg a cooker hood or extract vent above a shower, both vented to a heat exchanger or direct to external air.

Human activity (sweating, cooking, washing, breathing) in sealed poorly ventilated spaces tends to increase condensation.
Athletic levels of exercise within an apartment followed by showering and a steamed, boiled or friend meal would be an example.

If you don't properly ventilate a dwelling, moisture can build up over time in the surfaces of fabrics and walls leading to the growth of damp and bacteria.
This is more likely to occur during extended periods of colder, wetter weather 


ONQ.

[broken link removed]

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