The dew point is the temperature at which moisture in the air will condense on a surface. It fluctuates with the outdoor temperature and relative humidity, which have an inverse relationship to each other. Because cold air can hold less moisture than warm air, as the temperature falls the relative humidity rises and, when the temperature of a surface falls enough, it reaches the dew point—which is 100% relative humidity—and condensation forms. The window glass of an air conditioned home will be cooler than the outdoor air on a warm morning and reaches the dew point temperature before other outdoor surfaces. Occasionally, we get asked the question “Why do I have condensation when my windows are insulated?” An insulated window still has some heat/cold transmission, and the exterior glass surface will still be slightly cooler because of the chilled indoor air. Trying to determine why one window has condensate on it and a nearby one does not can get complicated due...