Condensation on inside of window and condensation on inside of window in cold weather...

Condensation can occur on any surface that is below the "dew point" of the air with which it is in contact. The "dew point" is the temperature at which condensation will occur for a given humidity level.

In most houses in winter, the inner surfaces of the windows are the coolest surfaces in the home. Condensation will typically appear there before it appears on other surfaces. Condensation is less likely to occur on interior walls, because they are typically warmer than "dew point."

Occasionally however, condensation may occur on cold spots such as nail heads, in corners of outside walls where insulation is reduced, or in confined spaces where the circulation of warm room air is restricted. In extreme cases, condensation may lead to mildew and the growth of mold.

What To Do

To reduce or eliminate excessive condensation, the humidity level must be decreased and/or the ventilation increased.

To reduce humidity levels:

* Turn down humidifiers Ensure dryers are vented to the exterior

* Do not hang clothes to dry inside the house

* In extreme cases, operate a dehumidifier. Dehumidifiers generally are capable of removing 7.5 to 20 litres of water from the air per day.

Typical household dehumidifier.
A household dehumidifier.

To increase ventilation:

* Operate bath fans when showering or bathing

* Open windows or operate an exhaust fan as soon as significant window condensation appears, until the source of the humidity is remedied.

* Operate furnace with fan switched on for continuous air flow

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* Have range hoods vented to exterior

* In extreme cases, consider installation of an mechanical air exchanger or Heat Recovery Ventilator (HRV).

Heat Recovery Ventilator - A typical heat recovery ventilator.

If the obvious solutions dont eliminate the problem, before investing in a dehumidifier or an HRV, check the structure for other possible moisture sources. Ensure the appropriate insulation and moisture barriers are installed in the attic, basement or crawlspace. Check for seepage in the basement.

Attic ventilation is normally provided by vent openings in the soffits or gables and roof. The total area of ventilation should equal one square foot for every 200 to 300 square feet of ceiling area. Not less than 50% of attic ventilation should be throught the soffits or gables. Not more than 50% should be through the roof.