Inspecting windows after installation

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FenEx
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Re: Inspecting windows after installation

#16 Post by FenEx »

Interesting info HS!

I am very familiar with Stack, Mechanical and Wind effects on homes but this is the first time I have heard of "Shelf Effect" in windows. Can you share the poster's name?

The theory of a shelf effect seems only possible where there is no airflow or pressure influence. I don't wanna sound like Spock but that is Illogical. In forced air homes the supplies are located directly below windows and in radiant homes they are near by. Air won't sit if given any reason to move... it can't.

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Windows on Washington
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Re: Inspecting windows after installation

#17 Post by Windows on Washington »

FenEx wrote:Interesting info HS!

I am very familiar with Stack, Mechanical and Wind effects on homes but this is the first time I have heard of "Shelf Effect" in windows. Can you share the poster's name?

The theory of a shelf effect seems only possible where there is no airflow or pressure influence. I don't wanna sound like Spock but that is Illogical. In forced air homes the supplies are located directly below windows and in radiant homes they are near by. Air won't sit if given any reason to move... it can't.
I think that post was mentioned in regards to issues of condensation when looking at windows that have heavy drapes on them that are somewhat isolated from air movement.

Good to have you back Michael.

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HomeSealed
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Re: Inspecting windows after installation

#18 Post by HomeSealed »

There was no mention of window treatments by the Op, although tru_blu offered it as a possible cause in his post. Here is the link: viewtopic.php?t=1858 .... I thought the "shelving effect" was in interesting concept as it takes into consideration physical shape, and the fact that there would be reduced airflow in these areas... What is your thought on the last statement regarding the exposure of the bottom surface of the upper sash to colder tempertures, therefore making that glass edge(bottom of upper sash) the coldest ? That just seems like common sense.

FenEx
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Re: Inspecting windows after installation

#19 Post by FenEx »

It's not exposed to different temperatures from ambient interior air, but it is located at a considerable source of exterior, unconditioned air. Any airflow around the adjacent areas would create a positive or negative flow and thus still move the air unless the air was sealed on all sides.

Look at an airbrush... the paint is concealed in a bottle, but at one small point it has a draft moving across an opening... creating a pressure induced flow up a tiny tube with no problem, moving a fluid much heavier than air. Does it make sense that an open sash rail would protect air better and moving air would just pass by without effect?

For WOW: I thank you Sir. How the heck are things in DC??
I have a quick Certification training in Harrisburg, PA end of next week but next time I am out East we gotta do drinks or dinner.

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HomeSealed
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Re: Inspecting windows after installation

#20 Post by HomeSealed »

FenEx, I do understand what you are saying as far as the positive and negative airflow and agree that it plays a role, I'm just not certain that it is a full explaination in this situation... Here is a quote directly from Gorell which possibly explains it (shelving-effect) a little better:

Condensation often forms at the meeting rail and at the bottom of the lower sash on the interior of the glass. This is because when warm air cools, it falls down across the interior surface of the window at the same time the temperature of the air is falling. The air contacts the horizontal surface of the meeting rail, which acts like a dam, slowing the air's rate of fall and creating the perfect opportunity for the trapped water vapor to escape and form on the meeting rail's surface. The air then rolls over the edge of the meeting rail and again gains speed until it encounters the lower handle of the sash. At this point, the water vapor again makes its exit and lies at the bottom of the sash.

This would also explain why a sealed picture window will also show condensation first along the bottom edge of the glass. It is just the nature of condensation. This would seem to contradict your explaination above at least somewhat, as well as your comments citing the accumulation of gases in the bottom of the IG as evidence that the interlock is to blame.... and to clarify, I do not think that anything that you've said is completely incorrect by any means. My main points of contention were your statement that the problem must be a exclusively or even primarily due to a "poor interlock", and your questioning of my statement that the bottom edge of the upper glass sash will always be the first place for condensation, even if the interlock was completely sealed. All of my comments pertain primarily to those two points .. I appreciate your thoughts. :D

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Windows on Washington
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Re: Inspecting windows after installation

#21 Post by Windows on Washington »

Michael,

Give me a shout when you are out this way and we will definitely have to get some dinner.

Back to the point of the discussion, +99% of meeting/lower rail condensation is as a result of air leakage at those points.

A picture window showing condensation on the lower stile could probably just as easily be attributed to warmer air and interior temperatures being at higher points on the window. It takes very little air movement to disrupt this shelf concept and there is not a home (outside of purpose built tight homes) that is not moving enough air to disrupt these settling locations.

Take a smoke puffer and see how easily the air moves and will resist settling.

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HomeSealed
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Re: Inspecting windows after installation

#22 Post by HomeSealed »

Wow, again, I'm not trying to say that air leakage does not cause condensation or that any of the effects that you or Fenex have stated are false. It was stated that the OP's problem must be due to a "poor interlock seal". My point is that may or may not be true because 1. Every interlock is inherently going leak some air, saying that it is "poor" would imply a product or installation defect which may not be the case. 2. That even when all air leakage is removed, the lower edge of the glass on any window, particularly on the upper sash of a DH, will still be the first spot for condensation to appear (under ordinary circumstances). Fenex asked for some evidence/alternative theory which I provided. We can certainly debate the degree to which each of these effects are responsible for condensation, however it would be incorrect to say that any of them are false or irrelevant. That's all I'm sayin' :D

FenEx
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Re: Inspecting windows after installation

#23 Post by FenEx »

WOW or HomeSealed, Happy to discuss in further detail. WOW... screw dinner and lets cut right to cocktails as this crap could bore the best of us!!! I no longer have contact info so you gotta reach me! Michaell@midwesthp.com

HS... you are not wrong in theory... but what you suggest could only happen in an arena without airflow. Heated air rising, pressure differentials moving air from high to low, mechanical effects, wind effects through leakage... air with higher humidity pushing to a lessor..... these are all forces that contradict the simple theory of "shelf" effect.

This concept is easy disproved (in homes) using pressure diagnostics, thermography and chemical smoke.

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HomeSealed
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Re: Inspecting windows after installation

#24 Post by HomeSealed »

Fenex, would you agree that the lower edge of the glass is more often than not the first place for condensation on any window? ... I think that we can all agree on that. The question is why? I thought that the shelving effect made good sense and comes from multiple reputable sources, however, I have no trouble admitting that I do not know everything and there could very well be an alternative explaination... I wonder if you'd contribute your thoughts on what that would be.

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