Condensation: A Sign of High Humidity

Condensation is an unsightly problem. The last thing you want on your windows is a fog blocking the view. But the problem goes deeper than that—if condensation is a chronic occurrence in your home; chances are that you have excessive humidity. If water is accumulating on glass, it may also be accumulating on other harder to see surfaces such as wall and roof cavities. If left uncontrolled, excess moisture can have serious consequences, including:

• Mold or mildew
• Wood rot and warping
• Roof ice build-up
• Damp, ineffective insulation
• Discolored, blistered or bubbling paint
• Damaging moisture inside walls and attic

There are several ways you can reduce humidity in your home. 

You can determine how much moisture is in your home with an inexpensive Hygrometer that can be purchased from your local hardware store. Place the Hygrometer in your home for a few days and record the readings each day. Compare your data to the chart below. As outside temperatures drop, the indoor relative humidity level of your home should decrease. For homes with windows equipped with insulating glass, the University of Minnesota Agriculture Extension Service reports that the following humidity levels can be maintained in the home without causing window condensation. If your home’s relative humidity is higher than this chart, please consult Excess Moisture: Causes and Cures for tips on identifying and eliminating sources of excess moisture in your home. Outside Air Temperature with ideal inside relative humidity for 70° F (21° C) indoor air temperature:

• - 20° F (-29° C) outside should be 15% to 20% humidity inside
• - 10° F (-23° C) outside should be 20% to 25% humidity inside
• 0° F (-18° C) outside should be 25% to 30% humidity inside
• +10° F (-12° C) outside should be 30% to 35% humidity inside
• + 20° F (-7° C) outside should be 35% to 40% humidity inside

Cause	Cure
Inefficient windows with extremely cold glass surfaces	Install energy-efficient windows and doors. High-performance windows, such as those made with Low E II coatings with Argon gas, make the most of the sun’s heating rays during cold months and maintain a remarkable temperature difference between the indoor and outdoor panes of glass.
Inadequate ventilation of windows	Keep window coverings open during the day to allow air circulation and make sure patio doors have heat vents beneath them.
Moist air trapped in attic	Seal around indoor light fixtures to prevent warm, moist air from rising to the attic. Install soffit vents to prevent attic rot, making sure to keep vents clear of dirt and garden debris.
Radiator or kerosene heat	Use dryer sources of heat such as gas or electric furnaces.
Cooking and dishwashing	Vent stove range hoods and dishwashers to the outside. Cover pots while cooking.
Stale, damp air	Install an air-to-air heat exchanger to vent moist air outside. Some air quality systems recover up to 97% of the existing warmth and energy to heat incoming fresh air.
Showers and baths	Make sure bathroom exhaust fans are vented to the outside and use fans regularly.

Excessive humidity can actually be an issue in newer, energy-efficient homes that don’t “breathe.” An inexpensive hygrometer should be able to tell you if your humidity levels are in check.