# Condensation on plexiglass?



## Le_Marquis (Aug 11, 2015)

Hi,

In fall-winter-spring, I have lots of condensation on my double-pane original windows. After reading multiple sources on the Internet stating that condensation does not form on acrylic, I fastened a plexiglass sheet on a window to test. I lowered the double-cell cellular shades for the night.

This morning, I realized that the test failed - there was fogging on the bottom part (but no droplets).

So, what am I doing wrong?

Thanks for your help!


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## dd57chevy (Jun 21, 2015)

If your shades fit the window opening _too_ well , that _could_ be your problem . Try leaving a 2-3" gap (don't lower them all the way).


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## jeffmattero76 (Jan 4, 2016)

Where is the condensation on the double pane windows? Exterior surface, interior surface, or between the two panes? If it is between the two panes, it means the seal has failed and the window will have to be re-glazed to fix the problem. If they are double hung or sliding windows you would remove the sash, take it to a window manufacturer in your area, and they would replace the double pane of glass and the seal. I am in suburban philadelphia and that costs around $12 per square foot of glass. 

If the condensation is on the interior surface it means that the humidity in your house is too high. Typically, however, you see this in winter with houses that have humidifiers. 

If the condensation is on the outer surface, there is nothing to do. It simply means that the glass surface is cooler than the outside air, like what happens on the outside of your drinking glass.

I have never heard that about acrulic or plexiglass. Any surface that is colder than the air will cause condensation to form on it in a humid environment, as far as I know.

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## joecaption (Nov 30, 2011)

One other cause can be air leaks around the windows from lack of proper sealing before the trim went on.


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## Windows on Wash (Aug 30, 2011)

+1 to the previous question. Exterior or interior.


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## SeniorSitizen (Sep 10, 2012)

It would be interesting to see some of the references that state a plexiglass surface won't condense moisture.


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## Le_Marquis (Aug 11, 2015)

Thanks all for your help! 

Jeff- Condensation happens on the acrylic sheet that is fastened on the interior of the house. 

Joe - It could be. How do I know for sure? There is no trim on this window. 

Thanks!


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## Le_Marquis (Aug 11, 2015)

Senior Citizen - This is one such source - http://www.hydrosight.com/glass-vs-acrylic-a-comparision/

I found other sources too


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## Le_Marquis (Aug 11, 2015)

dd57Chevy - You are right, my double-cell shades fit too well. Only option is to leave gap? Nothing else?


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## Windows on Wash (Aug 30, 2011)

You have to allow roomside heat to reach the glass. If not, the glass temp goes down so low that you will have condensation at just about any relative humidity level.


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## dd57chevy (Jun 21, 2015)

Le_Marquis said:


> dd57Chevy - You are right, my double-cell shades fit too well. Only option is to leave gap? Nothing else?


I'm only _guessing_ , but I _have_ seen those insulated (accordion type) blinds cause condensation . I'm not putting them down , they are an excellent product . But if they are fitted too snugly , the airspace (between the blind & window) can't breath .

IIW you , I'd try leaving a gap tonight .

To answer your question , I don't know if they can be trimmed . But I wouldn't alter them _at least_ until you've determined they are causing the problem .


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## SPS-1 (Oct 21, 2008)

_The value of Thermal Conductivity is much higher for acrylic than for laminated glazing. For most types of acrylic is 0.19 W/mK. This means: no condensation on the acrylic window and few heat loss. Double glazing on the other hand is a much better insulator than even thick acrylic windows._

What you are doing wrong is believing everything you read on the internet. 

When the surface temperature of a piece of acrylic is below the dew point, you will have condensation. Period.

The poor grammar on the above quote makes me wonder if the guy's first language is even English. But to me, it is clear that he is saying that condensation has a *harder* time forming on acrylic than single pane glass, because acrylic is a better insulator than single pane glass. The above quote also says that double pane glass is a better insulator than acrylic, and I think we can all accept that condensation can form on the interior surface of a double pane window.


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## jeffmattero76 (Jan 4, 2016)

Le_Marquis said:


> Thanks all for your help!
> 
> Jeff- Condensation happens on the acrylic sheet that is fastened on the interior of the house.
> 
> ...


On which side of the acrylic sheet? The side closest to the glass or the side facing the room?

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## SPS-1 (Oct 21, 2008)

As shown below - cold acrylic plus warm moist air = condensation. 

Could be the humidity in your house is too high. Could be drafts around your windows. Could be not enough airflow in front of the window (i.e heat register below window but with air deflector on it). Maybe combination of all the above and a few other things.


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## Le_Marquis (Aug 11, 2015)

Jeff - condensation on side facing the room.

SPS-1. Humidity is high, around 50-60%, because I leave the windows open by day and close them at night. outside during the day it is about 18 Celcius and 50% relative humidity


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## SPS-1 (Oct 21, 2008)

50-60% relative humidity in your house in the winter seems high, and could be main problem. But the rest of what you just posted does not make much sense. Surely you don't keep your windows open all day in the winter. And you need to research the difference between relative humidity and absolute humidity ---- although it may be zero C outside and 80% relative humidity, cold air does not hold much moisture, so when you bring that cold outside air into your house and heat it up, its relative humidity would be very low. If you open your windows in the winter, you would have a DRY house. Where are you located? Do you have a reliable hygrometer, or are these estimates? 


http://joneakes.com/jons-fixit-data...r-level-of-humidity-for-a-house-in-the-winter


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## SPS-1 (Oct 21, 2008)

SPS-1 said:


> _The value of Thermal Conductivity is much *higher* for acrylic than for laminated glazing. For most types of acrylic is 0.19 W/mK. This means: no condensation on the acrylic window and few heat loss. _


I just noticed, that beside poor grammar, the person who wrote this is totally messed up. For low heat loss, you want LOW thermal conductivity, not high. Acrylic has a LOWER thermal conductivity than glass, not higher. Acrylic can be a preferred material because it has LOWER conductivity, not higher. 

R value is the inverse of conductivity, so acrylic would have a higher R value than the same thickness of glass.

Edit: I just looked it up --- the outfit that wrote this is in Germany. Probably used Google-Translate to write the English version. Possibly the guy is not totally out of it --- just a bad translation.


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