Weatherproof your windows

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Q: We have a two-story house built in 1939 with original double-hung windows in good shape and aluminum storm windows. In winter, the inside of the storm windows on the second-story (bedrooms) get some condensation on them. The house windows have metal weatherstripping (some missing).

Besides putting up foam tape around the house windows, do you have any suggestions without spending a lot of money to try to correct this? Also, is the condensation something to worry about? Could the condensation rot the window sill or something like that? I'd appreciate any advice. --Phil C.

A: There is a dead air space between the house windows and the storm windows, which is why having storm windows helps from an insulating standpoint. When air is allowed to move into that space, it carries moisture vapor with it, which then condenses on the cold glass and turns to liquid water.

To answer your second question first: Yes, the condensation is...