I've recently noticed that the windows on the south side of our house have condensation early in the morning. Since we made such a large investment in windows, and in particular in low-E, triple-pane glass, I was concerned that there was something wrong.
Interior condensation occurs in the winter and usually is a sign that cold air is coming in through your windows. When the cold air meets with the warm inside air, it results in condensation on the interior surface of the glass. Condensation is a sign of poorly performing windows and can cause wood to rot and mold to develop inside your home. However, the condensation on my windows is on the exterior, not the interior.
After searching the Internet, I found similar explanations to my window condensation issue. The clearest explanation was on the website of RLC Engineering. It said that low-E coating (which reduces radiant heat transfer) will tend to warm the inside surface in the winter, and the outside surface in summer sunshine. A low-E coating will also lower the outside surface temperature at night in the summer. Therefore, a low-E coating will reduce the potential for winter condensation, while creating more potential for summer condensation, especially if the inside thermostat is set near or below the outside dewpoint temperature.
Based on this information, I'm sure that the condensation in our house is a combination of our efficient, low-E coated windows in conjunction with the fact that our house envelope is incredibly energy-efficient, maintaining a more consistent temperature, therefore magnifying the difference between the changes in inside air and outside air temperature. It's a reassuring sign that my windows are doing their job, and apparently doing it well.
To learn more about Jason's new house and to see photos and previous blog posts, go to www.startribune.com/newhouse. Or e-mail him at hammond@mojosolo.com.
