Are your windows misting up on the inside, making it virtually impossible see out of? It is a common problem with low quality or improperly sealed glass units, and the only cure is to replace the unit with a new one. You can't see it, but double-glazed glass units are constantly expanding and contracting as they warm up and cool down throughout the day. the air or gas inside expands with the heat of the sun, causing the unit to balloon - this is known as thermal pumping. If the seal fails between the two pieces of glass, this allows moist air to be drawn in when the unit cools, and water droplets collect at the bottom. The next time the temperature rises these droplets try to evaporate but cant escape so they end up condensating on the inside of the glass, The level of moisture can sometimes be so great that it can start to fill up the inside of the glass unit.
