I was reading an interesting article from www.pressroom.pella.com about condensation. I was reading to see what reasons they gave and how to go about reducing it. Then this section came up about external condensation:

Exterior condensation on windows occurs primarily in the morning when days are warm and humid, but nights are cool. Typically, it clears as the day warms. Exterior condensation can occur at any time, especially in warm, humid climates where interior temperatures are cooler than outdoor conditions. Exterior condensation means that windows are doing their job properly. However, if you spot excessive condensation on the inside of your windows, check your inside humidity – it may be a signal of potential problems if not addressed.

The bit I’ve underlined is the bit which I tell our customers exactly to the word how they’ve described it. Is exterior condensation a bigger problem in the US than here? Maybe so if www.pressroom.pella.com have felt the need to explain it. 

Now that we are selling much more thermally efficient windows, we are going to need to explain to future customers that this scenario could happen from time to time. The good thing is that it only last a couple of hours, and is physical proof that the windows are doing their job…and we haven’t been just typical double glazing salesmen and just lied through our teeth!

The full article can be found here: http://pressroom.pella.com/fast_facts/87/