Windows Icing over

[jtfoxman]

I am having a problem with my windows icing over on extremely cold days. Our house has older wooden frame windows with only the upstairs having storm windows. So in the winter I cover all with the plastic insulation. Well in the upstairs ice forms on the inside of the storm windows and in the downstairs the ice forms on the inside of the window pane.
I am not sure what would cause this. Is our house to humid? Or is it the heat escaping throught the plastic and collecting on the windows.
Any ideas?

[Meffy]

Sounds like too much humidity indoors to me. I've got to install a ceiling fan in our main bathroom to vent the saturated air from showers outdoors so we don't have the same problem. (I suspect that's our main source of overly humid air.)

[edit] I'm no expert, this is an educated guess merely. But it seems a safe bet it's fairly close to the mark. What's causing the excess humidity is another matter altogether.