Energy efficiency is crucial in this climate of increased fossil fuel consumption. The windows contribute about 20% of heat lost from houses with old double glazed windows. The air gap between the sheets of glass in double glazed windows will fail over time.
Symptoms of failed double glazing include condensation on the inside of the glass layers. Replacing all your windows is the only solution when double glazing units fail. Replacing your windows with new double glazing is an option, but for a couple of hundred pounds, you can go triple glazing.