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<div class="moz-cite-prefix">Air flow through the window is not the
same as heat flow and in NO way will it always be in to out, hot
to cold. Within one window assembly air may even flow in two
directions, typically in such a case, in at the bottom and out at
the top. Your simple case is incomplete, but in any case pressures
do drive air flow, but not temperature difference (although
pressures can be established because of temperature but that is
not at all the same thing).<br>
<br>
I'd quibble with some other points you raise, but I can't pass on
the above.<br>
<br>
</div>
<blockquote cite="mid:508DD521.8060007@dnaco.net" type="cite"> Two
points, in response to two of your posts (bearing in mind that I
am speaking on the assumption of a cold climate). <br>
<br>
In a cold winter, without extreme exterior humidity and wind - in
coastal Alaska, for example - the flow through any leaks in the
window assembly will be from warmer to colder. The greater the
temperature differential, the greater the pressure driving the
leakage. So, "cold' air should not be leaking into the space
between panes because the air between panes will be somewhere
between the interior air temp, at the inside pane, and the air
temperature against the outside face of the outer pane.
Therefore, the air/heat flow will be from inside to out.<br>
<br>
Of course, that is the simple model. Solar loading and wind will
have their effects. Of course, the ideal is to have all
seams/joints in a window unit hermetically sealed, but that's a
hard thing to achieve and sustain over time. <br>
<br>
Adding appropriately sealed layers to the window units will change
the temperature of the air film under whatever conditions are
producing condensation, but any window can condense, given the
"perfect storm" of conditions. Look to the
RH/temperature/lifestyle conundrum for each "problem" window.<br>
<br>
The solution is to determine the RH/temperature combination that
allows the problem, then locate the moisture source(s) and change
them or the actions/assumptions which are causing the elevated RH.<br>
<br>
As Mr. Holladay points out, there are several ways to calculate a
given window's condensation likelihood ranges. Unfortunately,
these have to assume a standard set of conditions, which may not
match those at you home, for any give window or any given time.
For all of the complex factors involved, whether or not you will
have a condensation problem on any given window finally comes down
to the surface temperature of the window (which as he points out
varies for different areas of the window) and the dewpoint of the
film of air actually in contact with that window surface.<br>
<br>
Recommendations and RH guideline for house temperatures are useful
as starting points but, if you have a condensation problem, the
two approaches are either to experiment or to have an accurate RH
gauge to measure the room air near the window at any given time
and to get an accurate measurement of the window's surface
temperature. You will need some form of psychrometric chart to
look up the dewpoint for that temperature and RH. Someone will
need to chart those factors over the time the problem occurs, then
go looking for the excess moisture source(s).<br>
<br>
The chart can take a bit of practice to understand but there are
"slide rule' forms of the psychromatic chart, to more easily find
dewpoint. Bachrach makes a sling psychromometer which has a slide
rule built into the case, but it can be a pain to use. Electronic
psychrometers give dewpoint as an automatic function, but are
significantly more expensive.<br>
<br>
Reading the air film temperature or RH is difficult to measure;
better to use the room air near it and add a cushion. Trial and
error should show you a workable adjustment factor.<br>
<br>
Reading the window surface temperature can also be tricky. I have
the best luck with a quick response contact thermometer. Remember
the edge of the glass at the frame is the most likely spot for
condensation to start. (IR thermometers do not read accurately on
glass, unless they can be adjusted for the reflectivity, only
possible on some expensive models. You could use a "black body"
target to get around the reflectivity, but that is probably beyond
what you need to get into. <br>
<br>
I hope this is helpful.<br>
Bob Klahn<br>
<div class="moz-cite-prefix">On 10/28/2012 6:30 PM, Sacie
Lambertson wrote:<br>
</div>
<blockquote
cite="mid:CAM6L0t4GLPeOyYVJuDWCCvG9w9CS8LKAob67om8X4_x7ZdUjFQ@mail.gmail.com"
type="cite"><font><font face="verdana,sans-serif">thanks <font>for
the suggestion Cor<font>wyn but we have about 50 windows
in this house, all of them 9 year old Pellas (the only
manufacturer who would make my custom sized windows <font>within
my time frame--a long story here)</font>. I can't
possibly imagine building storms for the inside of
these.<br>
<br>
<font>Our indoor humidity is within the <font>suggested
range.</font></font><br>
<br>
<font>S</font><br>
</font></font></font></font><br>
<div class="gmail_quote">On Sun, Oct 28, 2012 at 5:24 PM, Corwyn
<span dir="ltr"><<a moz-do-not-send="true"
href="mailto:corwyn@midcoast.com" target="_blank">corwyn@midcoast.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On 10/28/2012 1:20 PM, Sacie Lambertson
wrote:<br>
Our windows are starting to condensate at the base on the<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
inside. Many of you have suggested this is the penalty
of winter.<br>
Isn't there anything I can do about it?<br>
</blockquote>
<br>
</div>
See my previous suggestion for interior storm windows.<br>
<br>
Here's the basics of when you will get condensation. When
the dewpoint temperature of the inside air is a the same as
(or greater than) the temperature of the inside surface of
the windows (or anything else in your house), that surface
will condense water. So in order to avoid condensation you
need to either lower the dewpoint of the air inside, by
reducing the humidity, or increase the temperature of the
inside surface of the windows.<br>
<br>
Whether the humidity is too high is a matter of perspective
and some controversy. Get a humidity gauge and measure what
yours is. Generally somewhere in the 40% - 60% range is
recommended, but balance is between being too dry (and the
dry throat and colds that that produces) and being too wet
and the mold and mildew (and the allergies that aggravates),
so decide for yourself. That said, lowering the humidity
will reduce the condensation (and vice versa). One of the
things we generally see is that as people increase the air
tightness of their house they need to go from worrying about
too low humidity to worrying about too high humidity. At
that point, you are probably in the place where you will
need to have supplemental ventilation (for fresh air
reasons), and an HRV will take care of the humidity issue.<br>
<br>
The other way is to raise the temperature of the glass.
Traditionally this was done by putting the central heating
output right under the windows so that hot air washed over
the surface warming it up. Now, the solution is generally
to increase the insulation value of the windows. The
interior storm windows are a cheap way to do this, adding
about R-2 to a window for about $1.50 per square foot (if
you make them yourself), I make them for around $4.00 per
square foot. Raising the temperature of the glass will also
increase comfort levels (even at the same air temperature.<br>
<br>
Thank You Kindly,<br>
<br>
Corwyn<span class="HOEnZb"><font color="#888888"><br>
<br>
<br>
-- <br>
Topher Belknap<br>
Green Fret Consulting<br>
Kermit didn't know the half of it...<br>
<a moz-do-not-send="true"
href="http://www.greenfret.com/" target="_blank">http://www.greenfret.com/</a><br>
<a moz-do-not-send="true"
href="mailto:topher@greenfret.com" target="_blank">topher@greenfret.com</a><br>
<a moz-do-not-send="true"
href="tel:%28207%29%20882-7652" value="+12078827652"
target="_blank">(207) 882-7652</a></font></span>
<div class="HOEnZb">
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