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Condensation on storm windows

I live in a 1920's house, climate zone 4, with the original interior wood double-hung windows and triple track storms on the exterior. We have quite a bit of condensation on the interior of the storms and a few of the windows are so bad they get a pretty thick ice buildup on the interior of the storm glass when it's really cold. I've even had to drill additional weep holes in the storms to let the water out when the ice melts. And it causes large ice cycles to form on the siding below the windows as the sun melts the ice then runs out the weep hole and refreezes.

I've started to weatherstrip the old wood windows and I'm planning to replace the storms with Allied storm windows this summer. What's the trick to reducing the condensation? It's obviously air entering the window cavity around the wood windows from the interior - but I've read that weatherstripping is sometimes not the best answer as the wood needs air to dry and the weatherstripping, or at least too much of it, could cause problems.

I've also read you don't want to seal up the exterior storms too much because you want fresh air from the outside to help reduce the condensation.

So, any thoughts on the best approach to weatherstripping or not, sealing up storms or not, etc.?


Asked by Michael Mohr
Posted Jan 13, 2018 1:05 AM ET
Edited Jan 13, 2018 7:33 AM ET



I also wanted to mention there is a decent amount of air that comes through the window weight pulleys so air is infiltrating the window weight pockets from the exterior. The house has vinyl siding over the original clapboards so I can't really address that problem yet.

But this summer I also plan to remove the old vinyl and probably the wood to reinsulate the walls and install new sheathing and siding. With this the window weight pockets with be sealed from air infiltration.

Answered by Michael Mohr
Posted Jan 13, 2018 1:10 AM ET


It seems that you understand the principles fairly well. With storm windows, the aim is to have a very low rate of air leakage at the primary window, and a little bit of air leakage at the storm window. You always want your storm window to be a little leakier than your primary window. That way, the air between the two layers of glass will be relatively dry air.

An excellent article detailing all the steps required to reduce air leakage in an old double-hung window is this one from Fine Homebuilding: .

The work is fussy and painstaking. There aren't any shortcuts.

For more information, see What Should I Do With My Old Windows?

Note: Even though it looks like I have posted just a single image below, I have actually posted two images. Each image can be expanded. First click the top half of the image, and then click the bottom half of the image, to see both images.


Sealing air leaks at windows 1.jpg Sealing air leaks at windows 2.jpg
Answered by Martin Holladay
Posted Jan 13, 2018 6:54 AM ET
Edited Jan 13, 2018 7:00 AM ET.


Martin - thanks for the information. Very helpful.

Answered by Michael Mohr
Posted Jan 16, 2018 12:02 AM ET


Looking further into storm windows and now I'm looking at Low E glass. I've read about the pros and cons of Low E glass on replacement windows but I was wondering if the same benefits apply to Low E glass on storm windows. Does it help reduce condensation? How much heat gain is lost in winter? Or does the heat reflected back in make up for the loss in heat gain from the sun?

And lastly, how much visible light is diminished or discolored? Maybe that depends on the manufacturer of glass/Low E coating?

I don't think cost will be an issue as the storm windows I'm looking at are expensive anyway and I don't have that many windows, so the upcharge won't be that much - just curious if there are any cons to using Low E glass.

Any comments would be appreciated. Thanks.

Answered by Michael Mohr
Posted Mar 21, 2018 4:51 PM ET

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