Walls & Ceilings

What Would Bob Do? Preventing Window Condensation

It's winter and I keep getting condensation on the inside of my windows. What's the solution?

When moist, warm air makes contact with a window-typically the coolest surface in a given space (at least during the winter)-condensation forms. That's because cool air cannot hold as much water vapor as warm air. If window condensation drives you crazy throughout the winter, I can recommend any number of solutions, most of which are geared toward lowering the relative humidity in your home. One or a combination of the actions listed below should do the trick. It may be worth it for you to purchase a hygrometer, an instrument that measures relative humidity, to assist you in your efforts to reduce household moisture.

• Operate room humidifiers strictly on an as-needed basis. If you are running a whole-house humidifier, reduce its output, then wait a day to see what happens. If the problem persists, turn the humidifier down even further. (It is usually necessary to do this only when outdoor temperatures drop below 20 degrees Fahrenheit.)

• Run the bathroom exhaust fan while you're showering and the range hood exhaust fan while you're cooking. Leave fans running for 10 or 15 minutes after either activity. Double-check that both of these fans-and indeed all the exhaust systems in your home-ventilate to the outdoors and not to the basement, attic, or garage.

• Inspect the entirety of your home-including the basement, roof, and plumbing-for evidence of leaks, because they can have a significant impact on relative humidity.

• If you're in the habit of drying your laundry on racks indoors, try suspending the practice to see whether that prevents window condensation from forming.

• Avoid indoor storage of freshly cut, nonseasoned firewood, because it contains a high degree of moisture.

• Pull back window treatments so the heated air in your home can raise the temperature of the window glass, thereby reducing the likelihood of condensation.

• Install storm windows, which can raise the temperature on the surface of your interior windows, keeping them from reaching the point at which water condenses.

In addition to high relative humidity, insufficient household ventilation can also cause window condensation. If you live in a climate with cold winters and your home is very tightly sealed-and if there are more than a few inhabitants, each of whom adds moisture to the home every day-consider a heat recovery ventilation system. This type of system controls the introduction of fresh air from the outdoors and the expulsion of stale, overly moist air from within.