Foggy Double-Pane Windows: Replace the Glass, Keep the Frame

If you see fog, haze or droplets between the two panes of a window, the seal around the sealed glass unit (IGU) has failed. The frame is usually fine. Natural Resources Canada's advice is direct: condensation inside a sealed double-glazed unit is best corrected by replacing the glazing unit, not the whole window.

So for most GTA homes, repairing a foggy window means replacing the glass unit and keeping the frame. This guide explains how to tell whether your frame can stay (it usually can), what the glass-only fix costs in the GTA, and the few cases where the frame, not the glass, is the real problem.

What fog between the panes actually means#

A double-pane window's glass is a factory-made sandwich. Two panes are held apart by a spacer. A primary seal (polyisobutylene) and a secondary seal (usually polysulfide or silicone) close the edges, and the spacer holds desiccant that soaks up moisture inside the cavity.

Those seals are never perfectly airtight. A little water vapour always creeps in, and the desiccant absorbs it until it's saturated. Once it's full, condensation appears between the panes and the low-E coating can start to degrade. By the time you see fog, the seal is broken, and if the unit had argon, that gas is already gone.

That moisture can't be wiped away from either side of the glass and won't resolve on its own. Before you book anything, rule out the two look-alikes:

• Water on the room side of the glass comes from indoor humidity, not a broken seal. Our winter condensation guide covers how to fix it.
• Dew on the outside surface on a cool morning is a sign the glass is insulating well.

If you're not sure which you're seeing, work through the tests in how to tell if your window seal is broken.

The fix, and the alternatives, at a glance#

When replacing just the glass is the right call#

NRCan notes that when only the glazing needs replacing, you can buy a new sealed glazing insert and keep frames that are in good condition. A glass-only job is the right fit when:

1. The frame has no cracks in the vinyl, wood or aluminum.
2. The sash opens, closes and locks smoothly.
3. Your only complaint is fog or condensation between the panes.
4. The window is roughly 20 years old or newer and otherwise sound.

The work itself is simple. The glazing beads come off, the old unit lifts out, the channel is cleaned, the new unit sits on fresh setting blocks and the beads snap back in. That takes about 20 to 30 minutes per opening. The wait is in making the unit, which is built to your measurements and typically takes 1.5 to 3 weeks in the GTA.

A replacement unit brings the window back to its original spec. It doesn't turn a builder-grade window into a high-performance one. You can still specify low-E glass, argon and a warm-edge spacer at the same thickness, which often beats what was there before. Our low-E, argon and triple-pane guide explains the choices.

The exception: when the frame is the problem#

New glass can't fix a failed frame. It becomes a window-replacement job, not a glass repair, when:

• Rot at the sill or jamb of a wood window.
• A cracked frame or sash, which lets water into the wall.
• A sash that warps or binds, which usually means the frame is out of square.
• You want a change the frame can't take, such as a larger opening, a different style or triple glazing. Triple-pane sashes are 30 to 50% heavier.

If that's where you are, we'll tell you plainly at the visit rather than sell you glass for a window that won't last.

Don't let two foggy windows push you into replacing every window. Canadian double-pane units typically start failing somewhere between 10 and 20 years, sooner in harsh conditions and longer with a good warm-edge spacer, but they don't all fail together. A 25-year field study of more than 2,400 sealed units found 4.9% had failed at 10 years, 7.9% at 15 years and 9.2% at 25 years. Seals fail one unit at a time, often starting with the sun-facing ones, so replace the failed units and keep an eye on the rest.

Two questions people ask before a glass-only job:

• Permits. Swapping the sealed unit in an existing sash is generally treated as a repair. In Toronto, even replacing a whole window in the same-size opening of a detached, semi or row house with a single dwelling unit needs no building permit; other building types, and enlarging or moving an opening, do. See permits for glass repair in the GTA.
• Rebates. Ontario's Home Renovation Savings Program pays $100 per rough opening for whole ENERGY STAR windows and doors, and requires a home energy assessment and at least two upgrades. A glass-only swap generally doesn't qualify, because certification applies to the complete window. Confirm with the program, but a $100 rebate doesn't close the gap between a sealed unit and a new window.

Why defogging usually isn't worth it#

Defogging drills small holes in the glass, washes and dries the cavity, and then seals the holes or fits vents. It can clear the view, but it doesn't repair the failed seal or replace the insulating gas, so it won't restore the window's efficiency. Professional defogging runs about $75 to $200 per window. That's money spent on a unit that still has a broken seal. Our full defogging breakdown covers when it might still make sense.

What a foggy window fix costs in the GTA#

These are typical GTA ranges, not quotes. Prices depend on size, glass type, whether safety glass is required and how easy the window is to reach.

Warranty, insurance and condos: check who pays first#

Manufacturer warranty. Look along the spacer bar between the panes for a printed or stamped mark. Certified units carry a permanent mark identifying the manufacturer, plant and year of manufacture. Seal-failure warranties typically run 10 to 20 years. Labour is often covered for only the first 1 to 2 years, glass coverage is often prorated, and most warranties aren't transferable to a new owner.

Home insurance. Insurance covers sudden damage such as storms or break-ins. It won't cover a seal that failed from age, and deductibles typically run $500 to $2,000. Check your own policy.

Condos. In many Ontario buildings, windows and sliding doors are common elements, so owners can't replace them on their own. Your declaration decides who is responsible, so check it (or ask management) before you book work. This is general information, not legal advice.

Does waiting make it worse?#

A foggy unit isn't a safety emergency the way broken glass is, so you can take time to get quotes. It won't improve, though. Seal failure and gas loss can raise a unit's heat loss by up to 32%. Repeated wet-dry cycles also leave mineral residue that becomes a permanent milky film. If a winter draft or frost on the frame shows up alongside the fog, have the frame and weatherstripping checked at the same visit.

What we'd do#

On a foggy-window call, we start with the frame, not the glass:

1. Check that the sash opens, closes and locks properly, and probe wood sills for soft spots.
2. Read the spacer label to see whether the unit might still be under the manufacturer's seal warranty.
3. Measure the unit and note whether the location needs tempered safety glass, such as a door or a sidelight.
4. Recommend the glass package: usually low-E with argon and a warm-edge spacer at your existing thickness.
5. Install the new unit in your existing frame and give you an itemized invoice.

If the frame is failing, we'll tell you so: that's a window-replacement job, and we won't put new glass in a window that won't last. We serve Toronto, North York, Scarborough, Etobicoke and the rest of the GTA.

Next step#

If your frames are sound, a new sealed unit is usually the cheapest lasting fix for a foggy window. See how our foggy window repair service works, or contact us with a photo and rough size for a free quote.