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Condensation FAQ

Why should you care?

If left unchecked, a condensation problem in your home may cause rotting, peeling of paint, and the deteriorating of insulation and even buckled floors.

What can you do about it?

There are many possible solutions to the problem of condensation. If one solution doesn't eliminate the problem, try another - or a combination.

Measure the moisture

Some humidity is necessary for comfort and health. With many houses it is a struggle to keep enough moisture inside the house and maintain an acceptable comfort level for the occupants. Frequently humidifiers are installed to add moisture to the air but their use must be controlled or surface condensation problems may result. Unfortunately a dry house may indicate a high leakage rate (depending on the amount of moisture added by the householder) and contributes to concealed condensation. In some of the new homes, however, air leakage has been controlled to such an extent that the problem really is how Ito get rid of moisture. Yet many householders go on adding moisture to the air. The danger signal of condensation on windows, mould growth, or the damp spots on ceilings and room-side surfaces of exterior walls do not discourage them. Because windows do not provide much resistance to heat loss, they are often the coldest component of a building enclosure, and can be an indicator of humidity problems. As condensation occurs on inside window surfaces, whenever surface temperature falls below the dew point temperature of the room air, it may be a warning signal to reduce the humidity in your residence.

What can affect the performance of your windows?

The following may cause condensation to form on a windows at lower levels than given in the table.

Air Circulation
A window may be in an area in which there is poor circulation of warm air. This means that the temperature of the inside glass surface is colder than in other parts of the home and this may cause condensation to form at humidity levels which are practical for the rest of the home.

The figures in the table below are based on natural circulation of warm air on the inside surface of the window. By drawing heavy drapes or Venetian blinds over a window or patio door the possibility of condensation can be increased because the flow of warm air is restricted.

Varying Humidity Levels
Remember that the humidity in some rooms, kitchens and bathrooms in particular, can be higher than in other areas of the home, thus encouraging condensation to form on the windows in these rooms.

If windows are exposed to prevailing winds, then they will be slightly colder than the other windows in the home and may cause condensation to form at humidity levels which are practical for the rest of the home.

Some windows in the home may be protected by other buildings, trees, etc., which form a windbreak while others are totally exposed to the wind and, therefore, colder.

Wind Chill Temperature
Traditionally this has been the method used to relate wind and temperature. Usually traditional temperature readings do not include a wind chill factor. For example, with an indoor temperature of 20 decrees C and an outside air temperature of -12 degrees C the table below recommends a relative humidity of 30 percent. However, with an outside air temperature of -12 degrees C and a 20 kilometer per hour wind the outdoor wind chill temperature is -26 degrees C and so the level of relative humidity should be reduced to 20 percent.

Inside Relative humidity of 21oC with Double Glazing
Outside Air Temperature Indoor Relative Humidity
-28oC or below
Not over 15%
-28oC to -23oC
Not over 20%
-22oC to -17oC
Not over 25%
-16oC to -12oC
Not over 30%
-11oC to -6oC
Not over 35%
-5oC to 4oC
Not over 40%

How to Control the humidity in your home?

Ventilation is the most effective means for the house resident to remove moisture. By exchanging some of the drier outdoor winter air for warm humid interior air the moisture level will be reduced.

  • Opening a doors or windows for short periods can lose air from your home in large amounts simply.
  • Gas appliances produce moisture from combustion and cooking adds even more moisture - be sure to run your kitchen fan while cooking. It is necessary to vent the kitchen fan directly to the outside to achieve the desired effect.
  • Showers are a high source of moisture.
  • Bathroom doors should be kept shut and the exhaust fan must be running.
  • Clothes drying in the basement must be done in a dryer with an outside vent, hanging up clothes to dry must not be done in cold weather.
  • Shut off the furnace humidifier and any other humidifying device in the home.
  • If you have a fireplace, open the damper occasionally to allow moisture to escape.
  • Free air circulation is important. Do not cover hot or cold air registers. Leave bedroom and bathroom doors open.
  • Keep all rooms at minimum of 10 degrees C even if unoccupied. Condensation will occur in an unheated room.
  • Wipe up any tracked in snow before it melts and evaporates.
  • Floors wet from mopping can add large amounts of moisture. Run exhaust fans (bathroom and kitchens) while floors are wet. Do not wash floors on extremely cold days.
  • Most builders install a fresh air intake into the cold air return duct of the heating system. Make sure that the intake damper is open and that there are no obstructions to prevent airflow. If you do not have a fresh air intake, have one installed.
  • Caulk the perimeter of doors and windows to reduce air leakage.
  • Drapes and blinds should be left open during the daytime. At night leave Venetian blinds up off the frame to allow air to flow against the glass.

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