Condensation on the Inside of Windows: Causes and Fixes
Jan 13, 2026Condensation on the inside of windows is moisture in the room hitting glass that is colder than the dew point. In Chicagoland that happens a lot in winter, and it happens for more than one reason. McCann Window & Exteriors, Inc. gets calls that mix three problems: indoor humidity, a failed insulated unit, and a sash that leaks air. This page sorts them.
Wipe the water. Then decide which of the three you have. Treating all fog as a “new window” pitch is how people buy the wrong fix.
Room-side moisture on otherwise decent glass
Showers, cooking, a humidifier set like a greenhouse, and a tight house with nowhere for moisture to go. You will see beads at the bottom of the pane, especially on a polar morning. Run bath fans. Use the range hood. Lower the humidifier. Crack a sash for a few minutes if the house is sealed tight. This pattern often shows up on every north window at once. That is indoor air, not a factory defect on ten units the same night.
Fog between the panes
Haze, mineral staining, or fog you cannot wipe because it is inside the IGU. The seal failed. The gas fill is gone. Kits that “clear” it are a delay. Mark the unit for replacement. One failed IGU does not automatically condemn the house. Several on the same elevation, plus drafts, is a project.
Drafts that look like condensation
Air leaking at the lock or the meeting rail brings cold to the edge of the glass and can run moisture there. Weatherstrip, a sash that no longer squares, or an insert that was never sealed at the old frame will do it. A candle or a bare hand on a windy night is a crude but honest test.
What new glass changes
Warmer interior glass surfaces from a current Low-E package reduce room-side condensation for the same indoor humidity. They do not let you run a humidifier like a spa. Full-frame work can also remove a leak path the old frame was hiding. As a Pella Platinum Elite Certified Contractor, an Andersen Premier Certified Contractor with Marvin also available, we can show you real examples of each on the consultation, side by side, so the comparison is honest instead of one-sided.
When to call
Photograph the fog. Note whether it wipes. Note which rooms. Bring that to a measure. 35 years in this climate. About 50% repeat and referral. Crews 10 to 15 years. We don’t play pricing games. We show up. We clean up. We deliver what we promise. We would rather tell you to run the fan than sell you a window you do not need.
Baths, kitchens, and the obvious rooms
If only the bath fogs, start with the fan. If every north bedroom fogs on the same polar morning, start with indoor humidity and then look at glass temperature. If one sash is hazy between panes and the rest are clear, that sash is an IGU. Mixing those three stories is how a sales pitch gets sloppy. We would rather sort them.
Ready to improve your home’s comfort and efficiency? Call McCann Window & Exteriors at (847) 562-1212 or visit McCannWindow.com to schedule your free consultation today.
A cold-morning walk
Wipe room-side glass in the north bedroom, the kitchen after cooking, and the bath after a shower. Note which panes wet a towel. Look between lites of hazy units. Photograph stools. If only the kitchen wets after dinner, start with the hood, not a glass package. If every north IGU is milky between panes, start with replacement. If the stool is soft, start with the opening. Three jobs. McCann will do the window-shaped ones. 847-562-1212.
New windows can show more interior condensation because the house is tighter. Room-side water with a clear IGU is indoor air. Between-pane water on a new unit is a product problem. A certified product in a wet hole will still sweat the wall. Plants, aquariums, and indoor laundry are humidity machines — tell us how you live. 847-562-1212.
Do not caulk weeps shut. Do not blowtorch frozen glass. Storm panels can help old single-pane interior surface temperatures; on a failed dual-pane they are a bandage. We will name the wet surface: air, glass, or wall. 847-562-1212.
Bring the cold-morning photos. We will point to the wet surface and name the job: indoor air, failed glass, or the wall. Then we will do the window-shaped part from Northbrook. 847-562-1212.
