condensation on storm window

the inside of the storm window has moisture.
i have older wood single-pane windows, and aluminum storms.
this is only happening in upstairs windows. very odd.
i have read all previous posts about moisture on windows, but
still can't understand why this is happening.

i've weatherstripped the insides of the windows, held up a match to see if any air was escaping.
even took away some cord weather strip from the base of the storm to let some moisture escape, but nothing.
it's particularly bad if i close the shades at night.

it's NOT happening on any of the 3 skylights upstairs, so i don't think it's internal humidity.
how concerned should i be?
any suggestions for next steps?

 

The condensation on the storm windows is a direct result of heat dropping to dew point temperature on the storm window. Since you weather-stripped the windows and it is still occurring, may I suggest you cover one of your windows with plastic. If the next day the condensation does not appear on the storm window, then either the weather-stripping is ineffective or there is another source for the heat loss.

There are several possibilities here. At the bottom of this page is a link to the do it yourself hardware store. If you click on it scroll down to weather-stripping. There are a variety of different kinds that may be better suited for your application, V-seal is just one.

You want to inspect the wood window closely. You want to make sure it closes properly, check the bottom sill and the bottom of the window for excessive paint or debris to see if it is prohibiting the window from closing tightly. Do the same for the upper sash, but on top. If the window uses ropes or chains, tape over the pulley on the window jamb. Check the glazing on the outside of the wood window and for cracked glass. The concern with condensation on your storm windows is sill rot.

Condensation on windows concerning humidity levels in the home. There is a window condensation chart that indicates the recommended humidity levels in homes concerning different types of windows. What is meant by different types of windows is the different types of thermal resistance windows have. In other words, windows that have a low thermal resistance should have a lower humidity level in the home to prevent moisture from forming on their windows. So the 2 main factors with window condensation are the humidity level in the home and the thermal resistance of the window. In most cases this is very confusing to the average person. In this application, the condensation would occur on the inside of the wood window.

In your application, it does not apply. Rather, air leakage does. In other words, heated air is by-passing the wood window and condensing on the storm window. The Thermal-Moisture Dynamic concerning condensation on windows poses 3 possible sources for it, thermal resistance, humidity level and air leakage. Only air leakage is considered with condensation on storm windows. This assumes the normal operation of the window.

There is one other possible source for condensation on storm windows but you removed the rope caulking from the bottom of the storms. This has to do with the expansion and contraction of air between the storm and wood windows, which puts it outside the normal operation of the window.

 

i will investigage as you suggest, and try the plastic weatherproofing.
i can't tell you how much i appreciate your detailed response.
much thanks