There is an interesting condensation pattern on the inside of the
Even though neither side of the plastic (vinyl?) grids between the two
panes directly touch either pane, the grids still affect the R-value
near them (lowering it).
Outside temperature was below freezing; inside temperature at the
thermostat was about 70F.
Actually, it happened at all 10 double-hung windows in my house. They
are all from the same manufacturer, but I doubt every one would have an
imperfect seal. Even if the seals were imperfect, why would the
condensation show up in that pattern? And as I said the first sentence,
the condensation is on the inside of the inside pane, not between the panes.
Ron furnace blower. circulate indoor air taking in sosme fresh outside
air. If you have humidifier, lower the setting. Fogy window is not good
for the health of window. Our house is equpped with triple pane Argon
filled windows. I set humidistat at 25 to 30% during winter time.
Thing like that happen in really cold weather. If you measure the
temperature of the indoor side of the glass it is below the dew point.
Aside from "below freezing" there is little to go on. Pick up a
hygrometer and find out what the humidity is as a starting point.
The thermostat has an ON position that forces the fan to run all the
time. (Can't control the speed, however, from the thermostat.) But that
would create a chilly draft when the furnace isn't producing heat and
waste electricity. Also, two of the bedrooms are unused. I have their
ceiling supply registers closed and I keep their entry doors closed.
The humidity is added at the furnace by an Aprilaire unit. I have to
manually adjust the setting as directed by a decal on the control panel
that relates outside temperature to a dial setting. You can get the idea
from here if you zoom the photo and look at the upper right corner of
the control unit:
While the temperature is controlled closed-loop via the thermostat,
there is no closed-loop control of the humidity via a humidistat tied
into the Aprilaire unit.
I simply changed the Aprilaire setting to eliminate the problem. I
posted the photo here just as an education into the obscure behavior of
windows, even double-paned ones.
Have you ever done na energy audit? And look into running blower at
lower speed when you only need air circulation? I modified furnace
control and thermostat to do that. At lower speed you don't even feel
the draft. Sounds like your house may need to soup up the insulation
wherever it may need. Between furnace cycle if there is too much temp.
swing, that is one indication. Ideally indoor temp. should be kept near
constant at set point. In winter our 'stat is set at 21 deg. Celsius.
Temp. indoor is maintained between 20 and 22. Hardly feel any draft
between furnace cycles.
On Sunday, February 2, 2014 5:25:12 PM UTC-5, Tony Hwang wrote:
You can do all that and if you have a humidifier with the humidity
level set too high for the outside temp, you're still going to have
the same thing happen. Max indoor humidity should be 45% max when
it's around 40F outside. When it gets down to 0F, it should be about
20% max. When you see condensation like that, back the humditiy setting
On Sunday, February 2, 2014 4:14:11 PM UTC-5, Rebel1 wrote:
Of course there is a closed-loop control. The humidistat
that's mounted on the furnace plenum that you're adjusting
maintains the humidity at the level you set, just like the
thermostat maintains the temperature.
When it gets colder outside, you have to lower the humidity
level to avoid condensation. Or you can get one of the better
Aprilaire that have an outdoor temperature sensor that does
Nothing really obscure there, it happens all the time when it
gets cold enough outside and humid enough inside. They are just
panes of glass separated by a small gas filled space. The window
glass is going to be significantly colder than your walls that are
filled with 6" of insulation.
On 2/6/2014 8:53 AM, firstname.lastname@example.org wrote:
The other thing is that these humidstats are notoriously inaccurate with
age...there's no telling what it is actually responding at as compared
to the actual indicated setpoint. A secondary humidistat could indicate
just what actual range of RH is.
On Thursday, February 6, 2014 10:01:52 AM UTC-5, dpb wrote:
Agree. They are even inaccurate right out of the box. Many,
probably most of them, don't even have the dial calibrated by
humidity. They just have 1 to 7 or whatever. I think the one
the OP posted the link to is exactly like that.
Bottom line, if you have one of these and it doesn't have
automatic compensation via an outside temp sensor, you either
have to adjust it when the temp drops real low, or else set
it lower and leave it lower even when it's 40F outside.
Otherwise, you can expect condensation problems. That's why
I bought the Aprilaire with the outdoor sensor.
Not so happy with this one either. Overall, I think they make
great products. But the LCD display started failing on this
one when it was just 2 years old. Display is shot now, but
it still controls the humidity, you just can't see what
the humidity actually is.
On Sunday, February 2, 2014 10:03:27 AM UTC-6, Rebel1 wrote:
ough neither side of the plastic (vinyl?) grids between the two panes direc
tly touch either pane, the grids still affect the R-value near them (loweri
ng it). Outside temperature was below freezing; inside temperature at the t
hermostat was about 70F.
Everyone is making a simple thing as compicated as rocket science, just tur
n the humidity down when it gets REALLY cold!!!.
Condensation is formed when cold comes in contact with hot as you probably know.
Whether it's on the inside or outside of the window pain is irrelevant. It means
you have a problem with your windows.
Most double pain windows are filled with argon or krypton gases to slow the
transfer of heat through the window; however, after an extended period of colder
exterior temperature, the material ultimate achieves homeostasis from the
outside pane to the inside pane: BOOM! condensation.
What you need is new windows.
On Mon, 10 Feb 2014 03:44:02 +0000, WindowSpecialist
is high enough on the warm side and it is cold enough out side. There
is heat loss even from the BEST windows. If you know the "dew point"
of the inside air, at THAT temperature on the window surface you will
If you get FROST on the inside of the window either you have a window
problem or it is EXTREMELY cold outside.
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