You wake up on a cold Calgary morning and your windows are covered in moisture, foggy, dripping, or frosted at the edges. Window condensation is one of the most common questions homeowners ask, and the answer matters, because while some condensation is harmless, other kinds signal a real problem. At Window Craft, we help homeowners understand what their foggy windows are telling them. Here is a clear guide to why windows fog up and what to do about it.
The Three Kinds of Condensation
Where the moisture appears tells you almost everything about what is going on.
| Location of moisture | What it means |
|---|---|
| Inside surface (room side) | High indoor humidity |
| Outside surface | Harmless weather condition |
| Between the panes | A failed window seal |
That middle-of-the-glass fog, moisture trapped between the two panes where you cannot wipe it away, is the one that signals a genuine problem. The other two are usually about humidity and weather, not a broken window.
Condensation on the Inside
If moisture forms on the room-side surface of your windows, especially in winter, the usual cause is high indoor humidity meeting cold glass. Your home generates moisture, cooking, showering, breathing, plants, and when that humid air hits a cold window surface, it condenses, just like a cold drink sweats in summer. The fix is usually about managing humidity: use bathroom and kitchen exhaust fans, run a dehumidifier if needed, ensure good ventilation, and avoid over-humidifying in winter. Newer, better-insulated windows also have warmer interior surfaces, so quality vinyl windows condense far less than old, cold ones.
Condensation on the Outside
Sometimes you will see condensation on the exterior surface of your windows, often on a cool morning. Counterintuitively, this is usually a good sign. Exterior condensation typically means your windows are so well insulated that the outer glass stays cool while your home’s heat is kept inside, so dew forms on the outside as it would on grass. It is harmless and passes as the day warms. Nothing to fix here.
Condensation Between the Panes: The Real Problem
This is the one to act on. If you see fog or moisture trapped between the two panes of glass, and you cannot wipe it off either side, the window’s sealed unit has failed. The seal that holds the insulating gas between the panes has broken, letting moisture in. Beyond looking cloudy, a failed seal means the window has lost its insulating gas and its efficiency. This kind of window generally needs the sealed unit or the window replaced, which is where window installation in Calgary comes in. It is not something you can fix by wiping or drying.
When to Take Action
So, what should you do? Inside condensation calls for managing your home’s humidity and, if it is persistent, considering better-insulated windows. Outside condensation needs nothing at all. Fog between the panes means a failed window that should be assessed for replacement. If you are seeing widespread inside condensation on old windows every winter, or failed seals in multiple windows, it may be a sign that your windows are past their prime and an upgrade would improve both comfort and efficiency.
Frequently Asked Questions
Why do my windows fog up on the inside in winter?
Usually high indoor humidity meeting cold glass. Moisture from cooking, showering, and daily living condenses on the cold window surface. Managing humidity with exhaust fans and ventilation helps, and better-insulated windows condense far less.
Is condensation on the outside of my windows bad?
No, it is usually a good sign. It typically means your windows are well insulated, keeping your home’s heat in while the outer glass stays cool enough for dew to form. It is harmless and clears as the day warms.
What does fog between the panes mean?
It means the window’s sealed unit has failed, the seal broke and let moisture in, and the insulating gas has escaped. You cannot wipe it away, and the window has lost efficiency. It generally needs the sealed unit or window replaced.
When should I replace windows over condensation?
When you have failed seals (fog between the panes) in one or more windows, or persistent heavy inside condensation on old windows every winter. These signal windows past their prime, where an upgrade improves comfort and efficiency.
Clear Up the Confusion, and the Fog
Knowing what your foggy windows mean tells you whether to act. Window Craft assesses and replaces failed and inefficient windows across Calgary.
Call Window Craft at (587) 718-8851, or visit 2360 Portland St SE, Calgary, AB. We serve Calgary and area.
