How a sealed glass unit works
Most modern windows use a sealed glass unit (also called an insulated glass unit or IGU): two or three panes of glass held apart by a spacer around the edge. The edge is sealed, and the space between the panes is filled with dry air or an insulating gas such as argon. The spacer also contains a drying agent that absorbs small amounts of moisture.
As long as the seal holds, the space stays dry and the window insulates well. Once the seal fails, the drying agent eventually becomes saturated, and moisture starts to condense on the inside surfaces of the glass.
Why the seal fails
- Age. Seals slowly break down over years of service.
- Temperature swings. Glass and frames expand and contract with every hot day and cold night. Edmonton’s freeze–thaw cycles put extra stress on the seal.
- Direct sun. South- and west-facing windows heat up more, which ages the seal faster.
- Physical stress. A frame that’s out of square, a pressure washer aimed at the edge of the glass, or a manufacturing defect can all shorten a seal’s life.
Fog between the panes or condensation on the glass?
Not all fog means a failed seal. Try wiping the glass on both sides:
- It wipes off the inside (room) surface: that’s condensation from indoor humidity, common in winter. It’s a ventilation issue, not a broken window.
- It wipes off the outside surface: that’s outdoor dew, and it’s normal.
- It won’t wipe off from either side: the moisture is between the panes. The seal has failed.
Is a foggy window a problem?
A failed seal isn’t a safety hazard, but it does cost you. The insulating gas escapes, so the window loses some of its energy efficiency. Your view gets cloudier, and over time minerals in the moisture can leave permanent marks on the inner glass surfaces.
Can foggy windows be “defogged”?
Some services drill small holes in the glass to dry out the space between the panes. That can improve the look for a while, but it doesn’t restore the seal or the insulating gas. Replacing the sealed glass unit is the lasting repair.
How we fix it
We replace only the failed glass unit and keep your existing frame. We measure the opening, your new Low-E, argon-filled unit is made in Edmonton (usually in 2 to 3 weeks), and installation takes about 20 to 30 minutes per window. Sealed glass units start from about $300 each, with a $500 minimum for installed jobs. See foggy window repair for details, or read how much glass replacement costs in Edmonton.
Common questions
Will a foggy window get worse?
Usually, yes. Once the seal has failed, moisture keeps getting in, and mineral deposits can build up on the inner glass over time.
Do I need a new window if the glass is foggy?
Not if the frame is in good shape. The fog comes from the glass unit, so replacing just that unit fixes it.
Do replacement glass units come with a warranty?
Yes. Every sealed glass unit we install includes our premium warranty.
