A: Keep the curtains or shades open so that air circulates and warms the glass, even at night. Cold glass means more condensation.

But glass is only half of the equation. High indoor humidity means more condensation. So tackle the other side of the problem:

—Operate the kitchen exhaust fan every time you cook. Make sure the fan actually blows to the outdoors and doesn't just recirculate. Look in the cabinet above the fan. If you see ductwork, then the fan exhausts to the outdoors. If not, you have a recirculating fan, which does not eliminate moisture. In that case, you'll want to crack the window when cooking. (Some homes have downdraft exhaust fans with the vent housing under the cooktop.)

—Operate bathroom exhaust fans while bathing or showering and for 15 minutes afterward. You can increase ventilation in the home (bringing more fresh air into the home) by operating the kitchen or bathroom fan for some time every day, beyond when you're bathing and cooking. Cold winter air is dry, so this fresh air will lower the humidity in your home. Less humidity means less condensation.

—Do not vent the clothes dryer to the indoors.

—Use a hygrometer (available at hardware and home stores). The colder it is outdoors, the lower the humidity level should be indoors if you want to prevent condensation. Many homes in winter can't handle humidity levels above 50 percent. But if the humidity is too low, it can lead to dry skin, bloody noses and shrinkage in wood floors and chairs. A compromise is best, and the windows can be a guide:

If you have a little ribbon of condensation around the bottom of the windows, no problem. If you have to mop it up, it's too much. That can lead to mold and indicates that there could be larger problems in attic and wall cavities.