What causes “leaky seals”?

The glass panes of your windows are always in motion. Glass panes flex out in the heat of day and flex in at night as temperatures cool. Add Chinooks, and other sudden changes in temperature that Calgary is famous for, and you have the perfect recipe for foggy windows!  Here’s how the trouble starts:

Heating Phase of Windows

The inner airspace between window panes pick up heat from the sun or ambient air during the day. This increases the pressure inside of the window. As the pressure in increases, the glass flexes outward. When the pressure is high enough, some of the hot air expels through the semi-permeable seal.

Windows bow outwards when warming up.
The window heats up.

Cooling Phase of Windows

In the evening, the airspace cools. This decreases the pressure inside the unit and the glass returns to its normal position. Small amounts of air leak back into the unit to replace the expelled air. The spacer bar desiccant material sops up any of the moisture coming in from the outside air.

Windows bow inwards while cooling off.
The window cools down.

Where does the ‘fog’ come from?

The manufacturer accounts for  moisture by installing low-cost desiccant into the spacer bars. Because the amount of moisture over time is gradual, the desiccant generally holds up for ten years or more. The desiccant inevitably saturates (fails) and the airspace in the window becomes humid. When there is enough moisture to create fog, it’s time to call us!

You may have seen silica gel in your shoes!

Won’t my windows dry out on their own?

Because your window is still sealed, water continues accumulating. When the fog hits it’s dew point, it turns into water droplets. If left for too long, the droplets dissolve and corrode the the spacer bar. This dissolved material then gets baked onto the glass causing staining. These stains get will creep all over the window and bake into the glass causing permanent visual damage.  Yikes!

window with extensive silica staining
window with extensive staining.