Condensation on Windows - What's the deal?

A friend of mine has a 1950's house in which cheap replacement inserts were installed. He asks,

"Hey Abe, I want to pick your brain a bit. We have vinyl double hung windows in our home now with storms on the outside. When the weather cools down, moisture and frost almost immediately appears...a few of the storms are cracked so we ended up removing them yesterday, and they appeared to be pretty snugly installed, somuch that I broke a couple of the windows during this process since they were cracked already.

I'm not sure if the brand of windows matters, but do believe they aren't very high quality. Not sure if purchasing new storms would help? Any ideas or suggestions for a cost effective solution would be greatly appreciated."

The cause & solution depends: Is the frost on the storm window or on the interior window? Frost will almost always appear on the storm window and it usually indicates that the interior window is working OK! That's because it is keeping the heat in the house and the storm window is the cold surface.

However, it can occasionally indicate a different problem which is leakage of humid air from the house outside. This is sometimes from the replacement windows themselves, and other times due to the fact that they are an "insert" and there is leakage around them. It is hard to say.

I generally recommend leaving the storm windows in place. If the frost is inside the house, that is a different problem for us to talk about. That is probably a problem with humidity levels inside the home, or, having window coverings left down too long, or, in the mild fall weather, a VERY inefficient window.

You can also have a Home Performance with ENERGY STAR test completed to help determine other sources of air leakage and heat loss, and that testing will evaluate the potential energy savings from window replacement as well.