Condensation and Your Windows

Condensation and Your Windows

Sask Winter Condensation Concerns

Condensation Concerns

How to Reduce and Prevent Condensation


Each person has his or her own preference regarding the humidity level in his or her home.  If the occupants insist on a high level of humidity within the house, surface condensation must be expected when outside temperatures are low.  Some indications of surface condensation are:

Frost on door handles and hinges, or door frozen shut

Water or ice on windows

Damp spots or mildew on walls and ceiling

Damp spots or mildew on closet walls

Moisture on light fixtures

Moisture on water closets

Moisture on cold water pipes, walls and floors


Some humidity is necessary for comfort and health.  In many homes, it is a struggle to keep enough moisture inside the home to maintain an acceptable humidity 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 homeowner), which can contribute concealed condensation.

In some newer homes, however, air leakage is controlled so well that removing moisture from the house becomes a problem.  This problem is made worse by the use of humidifiers, resulting in condensation on windows, mold growth, or damp spots on ceilings and room-side surfaces of exterior walls.

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.  Because condensation occurs on inside window surfaces whenever the surface temperature falls below the dew point temperature of the room air, window condensation may signal a need to reduce the humidity level in your home.

WHAT CAN EFFECT THE PERFORMANCE OF WINDOWS (The following may cause condensation to form on a window at lower levels than given in TABLE 1)

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.

DRAPES- The figures in TABLE 1 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 ares of the home, thus encouraging condensation to form on the windows in these rooms.

ORIENTATION- 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.

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

WIND CHILL TEMPERATURE- This is 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 20C and an outside temperature of -12C, Table 1 recommends a relative humidity of 30 percent.  However, with an outside air temperature of -12C and a 20 kilometer per hour wind, the outdoor wind chill temperature is -26C and so the level of relative humidity should be reduce to 20 percent.



(Inside Relative Humidity of 21C with Double Glazing)


-28C (-18F) OR BELOW                                                  NOT OVER 15%

-28C(-18F) TO -23C (-9F)                                               NOT OVER 20%

-22C (-8F) TO -17C (-2F)                                                  NOT OVER 25%

-16C (-1F) TO -12C (10F)                                                 NOT OVER 30%

-11C (11F) TO -6C (21F)                                                    NOT OVER 35%

-5C (22F) TO 4C (40F)                                                     NOT OVER 40%



CONTROLLING HUMIDITY- Ventilation is the most effective means to remove moisture from your home.  By exchanging some of the drier outdoor winter air for warm humid interior air, the moisture level inside the house will be reduced.

  • Open a door or window for short periods to allow moisture to escape.
  • Gas appliances produce moisture from combustion.  Cooking adds even more moisture-be sure to run your kitchen fan while cooking.  Vent the kitchen fan directly to the outside to achieve the desired effect.
  • Showers are a high source of moisture.  Keep bathroom door shut and run the exhaust fan to eliminate moisture.
  • Clothes dryers should be vented to the outside.  Hanging up wet clothes to dry inside your home can add significant moisture to your home.
  • Shut off the furnace humidifier and any other humidifying devices in the home.
  • If you have a fireplace, open the dampener occasionally to allow moisture to escape.
  • Free air circulation is important.  Do not cover hot or cold air registers with furniture or appliances.  Leave bedroom and bathroom doors open.
  • Keep the temperature of all room at a minimum of 10C(50F), even if unoccupied.  Condensation will occur in a 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 kitchen) while floors are wet.  Avoid washing 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 dampener is open and that there are no obstructions to prevent airflow.  If you do not have a fresh air intake, have one installed.
  • Drapes and blinds should be left open during the daytime.  At night, raise blinds at least 100mm (4″) up off the frame to allow air to flow against the glass.
  • Certain fabric blinds that are designed to from jamb to jamb must be left partially open to ventilate the window cavity.  Failure to do this can cause extreme temperatures between the blinds and the glass.  Glass breakage or warping of PVC can occur, which can void warranties.
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