Window Condensation? Here’s Why…
When temperatures outside are low, you may notice some moisture on your windows (this can also happen in the Summer). Condensation usually happens when energy efficient replacement windows have recently been installed. The first inclination is that something must be wrong with the windows. However, the condensation is an indication that the windows are working as intended (and then some).
Winter condensation occurs on the inside, and summer condensation occurs on the outside. The problems with condensation are entirely visual, not structural. Since outside window and building surfaces often get wet from rain, a little extra liquid water will not be detrimental. The condensation disappears as outside air temperatures rise.
Energy efficient windows and window treatments reduce the heat moving through the window. The reduced flow of heat results in cooler surfaces on the cold side of the window and warmer surfaces on the warm side of the window.
So contrary to the natural initial reaction, condensation is actually a good thing. After all, reducing the flow of temperature through the window is the purpose of an energy-efficient window! However, at night during the summer, heat is radiated from the outside glass to the cold outside air. The low-E coating reduces the heat transfer from inside, so the outside glass surface can cool significantly below outside air temperatures. Under the right combination of inside temperature, outside temperature, and outside humidity, windows with low-E coatings or other energy-efficient treatments can develop summer condensation, while inefficient windows do not.
To prevent condensation, warm the surface air on the inside of the window during the summer and cool it during the winter. Since outdoor temperatures cannot be controlled, the way to preventing condensation is on the inside. Raising the thermostat setting a couple degrees is an effective way to warm the inside surface of the window which, in turn, warms the outside surface. Installing a deflector on a floor register or moving furniture can also help keep air-conditioned air from blowing directly onto a window. Exterior shutters, shades, window screens, or even trees can help reduce summer condensation problems, as well.