Was with a couple in Vienna, Virginia today picking out roof and gutter colors when they asked me to take a look at their bay window. It's a common bay window configuration with 2 double hung windows on either side, and an extra large picture window in the center. This picture window measured 73" by 47", or 120 United Inches.
When you have a window this large, it's common to have seal failure, and it's often the first to go before the remaining windows all begin to lose their seal as well. When a seal is broke, a vacuum effect takes place and all of the insulation gas is drawn out, and the air and moisture is pulled in.
Once you can see any condensation at all in a window, the seal is shot, and it's no longer energy efficient. This will fast become the coldest and the hotten seat in the house.