I have a fixed wood frame window with the glass secured by flat 3/4" strips
of wood on the inside. To prevent condensate forming between the two panes,
do I need to air seal the two panes or just secure with a second set of wood
It's not that easy a problem.
Condensation forms in proportion to the humidity of the air and the
temperature of the surface.
If warm, humid air leaks through the new inner pane and gets to the
cold outer pane, condensation will form on the inside of the outer
If cold air from outside leaks through the outer pane and cools the
inner pane, condensation will form on the inside of the new inner
Most window makers make the seals airtight and fill between the
panes with an inert gas. That's a great solution, as long as it
works. Once the seals deteriorate and air leaks in, the window
clouds and the entire glazing system needs to be replaced.
Pella windows let a small amount of outside air between the panes.
That seems to prevent any condensation between the panes, but
doesn't allow the inner pane to cool to the point where indoor
humidity condenses inside.
So, to put it simply, you're trying to replicate the results of the
best window manufacturers and their labs in a jerry-rigged system.
The answer, I think, is that you won't be able to do so very
satisfactorily, and you'd be better off getting a real 2-pane
window and installing it.
To reply by e-mail, remove the obvious word from the e-mail address
I asked a glass man about this once, and what he showed me was an aluminum
strip with desiccant inside about 3/8 thick. this would be placed between
the two panes and them a sealer was used all around. This whole unit was
then set into the frame.
This set up might be suitable with your situation.
About the time I had mastered getting the toothpaste back in the tube, then
that's the only real solution. take off the moldings and take a good
measurment of the glass inthe window opening. then go see your local glass
shop and order at minimim a 5/16" insulated unit. do not measure the glass
tight from side to side, you want at least 1/8" less on your width and
height measurements. he'll tell you about installation tips, but it's easy
and do not re-use the old moldings they will need to be trimmed down to
allow for the new thickness of the unit. you can use flat stock material,
but make sure your bottom and top are installed first. you can use latex
caulk on the outside to make a good seal on glass to wood moldings for
painting purposes, but set the new unit in a clear silicone on the backside
or interior side of the opening *or* if the window is set from the inside
do the opposite.
good luck...and make sure the opening is square before ordering anything.
Be sure to do some cost calculations first. I considered replacing the
single glass windows with double paned insulated glass in my Minnesota house
a few years ago. I was going to use the existing sash and replace only the
glass. I gave up on the idea when I calculated the payback to be something
like 15 years (if I remember right). Going from one pane to two only
increases the R value from about 1 to about 2 which is still very low. Such
a small change in thermal transfer for such a small area does very little to
improve heat loss and insulated glass is expensive.
Going to insulated glass may offer the benefit of more comfort if you're
sitting near the window, but don't count on it to save you any money.
Spending money on air infiltration by weather stripping is much more cost
I agree but, I'm only spending $2000 to replace 10 large windows averaging
20sqft each, with low-e argon which increases the R-value from 2 to 4 for
only 20% more. I expect to receive approx $1500 in rebates which makes my
net cost about $500. My main concern is comfort and resale value not payback
but I just could not resist such an excellent deal. Of course my labour is
Reducing air infiltration, increasing attic and basement insulation are all
part of the project.
If your in a mild climate, you will probably be ok with fabbing your
own dbl panes. My dad (Atlanta, GA) slaps a piece of plexiglass over
the windows (interior side) in the heating season to create a temp dbl
pane. Doesn't have any problems with condensation. Here in central TX I
have taken apart dbl pane windows to clean out the smoke (damn my
renters that smoke)that leaked in and then reassembled/installed. No
problems, didn't even use any sealant. The problem with sngle panes
around here is when a cold front blows thru and the temp drops 20dg in
1hr, the humid air inside the house condenses on the now cold glass.
Some day I will try making my own dbl panes. Awhile back I checked on
buying some of the spacer strips, they contain dessicant and have the
adhesive preinstalled. About $1 per ft and that was a few years ago.
That adds up fast, I will first try the wood strips. Also, the bigger
the space the better the insulation factor.
I will have to dig out my HVAC manuals to check but seems that the
table showing R values for dbl pane windows indicated that the bigger
the air space the better the R. seems like the triple pane were very
impressive. My previous house (central TX) had storm windows
installed. They created not much more than a primitive dble pane, maybe
a couple inches of air gap. Never had any condensation problems but I
am sure they are not very airtight. Wasn't insulation value the
marketing hype back when these things were sold? Guess they are
obsolete now with dbl pane windows so prevalent.
You are not going to be able to seal those panes will enough to keep the
moisture out of them. Even the manufactured windows can loose their seal
and when that happens, they cloud up quickly. Yours will not be that tight.
Your only home made solution is to vent the windows to the COLD side
"generally outside" That air is drier than the air inside. The other way
the warmer moister air will reach the cold outside window and condense on
it. Make sure you have a way of disassembling this window from time to time
as some dust etc. will get between the glass and need to be cleaned off.
You may want to see if you can mount a thermo-sealed window in that
space. You can buy the sealed glass units in any size you need at prices
that may be a lot less than you think. Most larger cities have local shops
that will make them up for you.
Thanks for all the replies!
I'm replacing 10 single pane windows with double low-e and will have a lot
of glass left over.
This window is quite small 31/2' x4' and set in stonework so I think I'll
just add another pane (removable) and see what happens. I can always replace
it with a sealed unit later. Temperature here rarely goes below freezing.
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