About Donald Bosch Expertise I can answer any question relating to windows & doors, glass and mirror, including performance specs, insulation specs, installation and design.
Experience I am a retired window & door specialist, having had related businesses in the industry for over 20 years. I also have very good knowledge of glass, sealed units,(thermal glass) insulation.
Education/Credentials Many industry related technical courses and seminars and a lengthy career in sales with large manufacturers.
Question We can't see out our new windows! I live in Wisconsin- Brookfield (by Milwaukee). In the early morning until about 9am now in the summer, the windows are all foggy except around the edges. They are Pella windows, replaced in November. The window company says the windows are working fine, it is just humid outside. Yours is the first answer that might help me, as most others are baffled. Can I take your questions from the last answer, do they apply to my problem with condensation on the outside? The contractor said my 20 year old windows had leaks around them so that is why it didn't happen before. These windows came with all the woodwork and vinyl surfaces on the outside. They were a fortune. It looks ridiculous. What should I do?
Answer HI,
There is indeed nothing to worry about. This condensation on the outside of your windows is normal and is caused due to the dew point of the exterior air with regards to the temperature of your exterior glass.
Summer condensation occurs when the outside window surface is cooler than the dew point temperature of the outside air. In the southeast US, summer dew point temperatures range from about 65F to 75F. When temperatures inside the home are within this range, summer condensation problems can occur.
The outside glass surface in energy efficient windows will be closer to the outside air temperature, while the outside glass of an in-efficient window will be closer to the inside temperature. Low-E coatings help reduce the amount of radiant heat transfer through a window. As the summer sun warms the outside glass, a Low-E coating reduces the amount of this heat that moves inward. (The outer glass can warm significantly in the sunshine. During the winter, the inside glass is warmer because of the reduced radiant heat movement outward, and you don't get that "cold" feeling sitting next to a window.) At night during the summer, heat is radiated from the outside glass to the cold sky and other objects. The Low-E coating reduces the heat transfer from inside, so the outside glass surface can cool significantly below outside air temperatures.
In cases where the inside temperature is below the outside temperature, a Low-E coating will allow the outside glass temperature to drop to about the same as that of an inefficient window. In cases where the outside air is colder than the inside temperature, a Low-E coating allows the outside glass to get even colder. Therefore under the right conditions, windows with Low-E coatings can develop more summer condensation than inefficient windows.
Since we cannot control the outside dew point temperature (or relative humidity), the options for preventing summer window condensation problems are to warm the inside surface of the window as a way to warm the outside surface. Raising the thermostat setting is about the only option. Exterior shutters, shades or even trees can help reduce summer condensation problems as well.
Thus, condensation occurs when a surface falls below the dew point temperature of the air. The outside glass in an energy efficient window will be closer to the outside temperature, and the inside glass will be closer to the inside temperature. The glass in an inefficient window will be more heavily influenced by both inside and outside temperatures.
