Window condensation is a frustration for homeowners, especially if their windows are new. Immediate thoughts are of mold, water damage, peeling paint and reduced energy savings. To help our customers prevent window condensation, we need to understand why condensation occurs and how to prevent it.

Humidity and Condensation 
Condensation occurs when there is a reduction in the rate of air exchange (i.e. closing windows in winter) and there is excess humidity in the home. Humidity is the amount of moisture or water vapour in the air. People and pets produce moisture when they breathe or perspire. Even indoor plants produce moisture. We add water vapour to indoor air through everyday household activities: cooking, showering, bathing and doing laundry. Every time you run the dishwasher, you add 5 lbs of moisture to your home! 

We need humidity for our comfort and health. But too much or too little humidity can produce a host of difficulties in homes. Some of the problems are just nuisances like condensation on windows and musty smells, others can be more serious such as wet stains on walls and ceiling, moldy bathrooms and allergic reactions. Humidity hassles often occur during the colder months when windows are closed, and indoor air circulation is reduced.

Humidity Levels 
Experts have developed rules of thumb to help homeowners make decisions regarding humidity levels in their homes. The limits should be used as guides only. Acceptable or comfortable humidity levels will vary from season to season, from house to house, and even between rooms in the same house. To measure the indoor humidity in a home, you can purchase a small inexpensive tool called a hygrometer that measures relative humidity (RH). The recommended indoor relative RH when the outdoor temperature is above 10° C is 30 to 50 per cent. When the outdoor temperature is below 10° C, the recommended RH is 30 per cent. 

How Our Windows Help 
We use warm edge technology on all our windows and doors, creating an insulated air space between the glass units. Warm edge spacers also keep the edges of your window glass warmer, reducing condensation. 

Double and triple glazed windows ensure the humidity inside the room can be higher than a room with ordinary single glazing before condensation occurs. Because the units are sealed at the factory, condensation between the panes of glass does not occur. 



The first step of preventing condensation is controlling humidity. Begin with installing new energy-efficient windows with a high performance rating. Highefficiency windows may not solve all condensation concerns, but properly installed, sealed and insulated windows are the first step towards eliminating humidity issues. Although excessive humidity shows up as condensation on the cold surface of a window, the window is probably not the source of the condensation problems. 



Further reducing humidity in homes is not difficult. Begin by remembering to open or close doors and windows on a periodic basis to exchange air in the house. Exhaust fans may have to be installed in bathrooms and kitchens, and seal up the house with weatherstripping and caulking. Humidifiers, both stand alone or attached to furnaces, can be sources of excessive moisture and mold, so ensure they are not overused.

Tips to prevent window condensation:

• Install an air exchange unit or a humidity control device to maintain the proper level of humidity
• Insulate water pipes
• Ensure hot air from registers does not flow directly on to the interior surface of the glass
• Turn furnaces with humidifiers off until condensation reduces
• Ensure the exhaust from the clothes dryer is vented outside
• Cover crawl spaces with 0.15 mm (6 mil) polyethylene
• Ensure gutters drain water away from the house
• Avoid drying firewood in the house
• Waterproof damp basement walls and floors
• Use exhaust fans while cooking
• Open a window when doing laundry
• Close the bathroom door and open a window after baths and showers
• Ventilate the home at least once a day

Outdoor Condensation*

Condensation on the outdoor surface of an insulating unit is not an indication that the glass or insulating unit is defective. Under the right set of atmospheric conditions it is possible to get condensation on the exterior glass surface of an insulating glass unit. Specifically, the following conditions:

• Glass temperature below dew point temperature
• Clear night sky
• Still Air
• High relative humidity
• Well insulated glazings

Exposed to these conditions, the exterior surface of the glass can radiate heat away to the night sky such that the glass temperature falls below the dew point of the ambient air. When this occurs, moisture from the air condenses on the glass surface. Only when the glass temperature rises above the dew point will the condensation evaporate back into the air. Dew formation on grass, car hoods and roofs, and building roofs and walls is common and accepted as a fact of nature.

The presence of moisture indicates that a specific set atmospheric conditions exist and that the insulating glass is indeed doing its job – that of insulating the building from the environment. In this case, that insulation capability is what retards the flow of building heat through the glass and prevents warming of the exterior above the dew point.
If exterior condensation occurs on insulating glass, there is little or nothing that can be done to prevent its reoccurrence. Draperies should be open to allow as much heat transfer though the glass as possible. Trees or buildings can block the radiation view to the sky. Shrubbery immediately adjacent to the glass can increase the local humidity and may need to be moved. The exterior surface of the glass will warm and the condensation will evaporate when either the heat loss to the sky is blocked (i.e. clouds), the wind picks up, or sunlight is absorbed on the glass surface.

*Source: Cardinal Glass