PROBLEM: My window is fogged up.

ANSWER: First, you must determine if the fog is inside your home, between the glasses of the sealed unit, or even in some cases on the outside of the glass! Remove the screen if the window is a casement or awning. Touch the inside glass. If you can touch the moisture, you probably have a condensation problem.

-Condensation will occur on any surface where the surface temperature is lower than what is necessary to support the level of relative humidity in the air. This is not a window problem but is an airflow and humidity issue in your home. Check your relative humidity near the window with a barometer. Compare your humidity and exterior temperature to the following chart. (You may choose to live with a degree of condensation if the high humidity is a more comfortable living environment, while the humidity may be causing hidden damage to other parts of your home, it will not hurt your vinyl windows.)

Outside Air Temp (Celsius) – Indoor Relative Humidity (%)
10 70%
5 60%
0 55%
-5 45%
-10 40%
-15 35%
-20 30%
-25 25%
-30 20%
-35 15%
-40 5%

If the air circulation in the room with the fogging problem is poor, you may have fogging at even lower levels of relative humidity.
To eliminate fogging, there are two approaches and a variety of solutions. Try various combinations to discover what works for you!

  1. Lower the humidity in the room.
    A. -Moisture in your home is created from cooking, washing, watering plants etc. Check to make sure that where ever possible, moist air is immediately directed out of the home. Accomplish this by having and using good venting systems in your washrooms, attached to your clothes dryer, over your stove etc. Move plants that require high amounts of water to a less sensitive location in your home.
    B. -Blinds, curtains (even gauze!) and other window treatments will trap air next to the glass and lower the surface temperature of the glass. Leave treatments as open as possible, particularly at night, in order to maximize air movement st the window.
  2. Raise the air temperature at the window.
    A. -Add heat to the room by redirecting airflow to increase the flow of warm room air across the window. Redirect air from nearby heating sources toward the window. If the air in the room in general is cold, raise a local thermostat or use a space heater. Remove heat deflectors from below windows so heat will flow across the glass surface.
    B. -Turn off any central or room specific humidifier. Add a dehumidifier to the specific location. Opening a window a crack will allow drier outside air to mix with the air in your room. As it warms, it will lower the room’s relative humidity. Since health requires numerous full changes of air in a living space, this is not a waste of energy.

Exterior fogging:
If the moisture is clearly on the outside of the home, you have achieved an extremely efficient home system! This can occur when your glass is cold because heat is not leaking through from your home. It is a goal that thermal engineers strive to achieve!

Moisture between the panes of glass:
This is a seal failure. Consult your warranty for details on receiving service to replace the failed glass unit

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