Does a failed desiccant explain a cloudy Ottawa window?

Yes, a failed desiccant is almost always the reason for a cloudy or foggy window in Ottawa homes. When you see that milky haze or condensation trapped between the panes, it's a clear sign the insulated glass unit (IGU) has failed.

How the desiccant works — Every double or triple-pane window contains a small amount of desiccant material (typically silica gel or molecular sieve) packed inside the spacer bar that runs along the edge of the glass unit. Its job is to absorb any residual moisture trapped inside the sealed unit during manufacturing. As long as the seal is intact and the desiccant is active, the space between the panes stays perfectly clear.

What causes desiccant failure — Over time, the perimeter seal around the IGU degrades. Ottawa's climate is particularly hard on window seals because of the dramatic temperature swings — from -30°C winters to +35°C summers. Every day, the sealed unit expands and contracts with temperature changes, slowly fatiguing the seal. Once even a tiny breach forms, humid outdoor air begins cycling in and out. The desiccant absorbs moisture at first, but eventually it becomes fully saturated and can no longer do its job. At that point, moisture condenses on the interior glass surfaces and you get that permanent foggy appearance.

Ottawa-specific context — This problem is extremely common in Ottawa homes built in the 1990s and 2000s, when double-pane windows became standard. Those original IGUs are now 20-30 years old and reaching the end of their service life. The freeze-thaw cycling Ottawa experiences — sometimes multiple times in a single week during shoulder seasons — accelerates seal degradation faster than in milder climates.

What your options are — A failed IGU cannot be repaired by reactivating the desiccant. The moisture contamination and seal failure are permanent. Your realistic options are either IGU replacement (replacing just the glass unit while keeping the existing frame, if the frame is in good condition) or full window replacement (new frame and glass). If your frames are older, warped, or drafty, full replacement usually makes more sense and gives you the opportunity to upgrade to a modern triple-pane, Low-E, argon-filled unit — which performs dramatically better in Ottawa's Climate Zone 6 conditions.

To get your fogged units looked at and priced, send the details through Ottawa Window Pros — an installer can tell you whether replacing just the sealed unit or the whole window is the better call here.