Window Repair or Replacement: Fogged Glass, Drafts, Rot, Stuck Sashes and Condensation, and Which Ones Are a $250 Fix

Windows & Doors

Repair or Replace? The Glass Is Fogged, the Room Is Cold, and the Salesman Says Eighteen New Windows

A window has four parts that fail on their own schedule: the sealed glass unit, the weatherstrip and hardware, the frame, and the installation around it. Only one of them is a reason to buy a new window. The other three are a glazier, a bag of parts, or a tube of foam. Here is how to tell which one you are looking at before anyone measures anything.

Ontario repair prices, October 2026, before HST.

The numbers

ProblemWhat it usually isRepairReplace instead when
Fog or streaks between the panesFailed seal on the insulated glass unit$250 to $450 per sash, new sealed unitThe frame is also rotten, or the unit is an odd shape nobody stocks
Cold draft at the sashFlattened weatherstrip, a lock that no longer pulls the sash tight$40 to $150 per windowThe sash is warped and will not meet the frame anywhere
Cold draft at the edge of the frameNo foam behind the casing; fibreglass stuffed in the gap in 1988$75 to $150 per window: pull the casing, foam, re-trimNever, on its own. This is an installation fault, and a new window set the same way does the same thing
Casement will not crank, or droopsWorn operator or hinge arm$60 to $180, parts and an hourParts are no longer made for that series (common past 25 years)
Slider is stiff, or falls off its trackRollers, track dirt, a bent track$40 to $120The frame is out of square
Water on the inside of the glass in winterHouse humidity, not the window$0 to $400: hygrometer, exhaust fans, an HRV settingRarely. Condensation on a triple-glazed window is still your air
Soft wood at the sill or lower frameRot, from years of condensation or a leak above$300 to $700 with epoxy and a new sill nosing, if caught earlyThe rot is past the sill, or more than two windows have it
Water stain below the window on the drywallFlashing or sealant failure around the frame$150 to $500 outside: re-caulk, re-flash the headFull-frame replacement if the sheathing behind is wet. Leaks

The one that is really a replacement: the frame!

Glass can be swapped. Hardware can be swapped. Weatherstrip is $12 a roll. The frame cannot be swapped without taking the window out, and that is a replacement by definition. So the test is the frame. Push a screwdriver into the bottom corners of the exterior sill and the lower side jambs. Solid: everything else on this window is repairable. Soft, flaking, or the screwdriver goes in a quarter inch: the window is done, and it is a full-frame replacement, not an insert, because an insert goes inside the frame you just found rotten.

Vinyl frames do not rot, but they do crack at the welded corners, warp in dark colours facing south, and go brittle past 25 years. A vinyl frame with a split corner is also done.

The fogged-glass trap

Fog between the panes means the seal around the insulated glass unit has let go and moisture got in. It looks terrible and it is cosmetic: the frame, the sash and the hardware are as good as they were last week. The fix is a new sealed unit, made to the size, swapped into the existing sash by a glazier in twenty minutes, $250 to $450 depending on size and whether it is tempered. Sealed units for 1990s and later vinyl are easy. Units for 1970s wood windows with putty glazing are harder and sometimes not worth it.

The window companies know this. “Your seals have failed, the windows need replacing” is the most common sentence in the trade, and it is half true. If five of eighteen windows have fogged and the frames are sound, five sealed units is $1,800. Eighteen new windows is $20,000. A company that only sells windows is going to say the second thing.

When replacement is the right answer

  • Rotten frames on more than two windows, or past the sill on one.
  • Original aluminum or steel windows with no thermal break: ice on the inside of the frame every January is the sign.
  • Single-glazed wood windows with storms, if the storms are gone or you are tired of them. Repairable, but the energy gap is real.
  • Hardware no longer made and the window will not lock. An unlockable casement is a security problem, not a draft.
  • You are doing the siding. The 40% extra for full-frame is cheap while the wall is open.
  • More than a third of the windows have two problems each. At that point the repair bill and the disruption start to look like the replacement bill.

The how-long-do-windows-last page has the ages at which each type usually crosses the line.

Where homeowners go wrong

  1. Letting the window company do the diagnosis. Get a glazier or a handyman to price the repairs first. Then get the window quote. Compare.
  2. Replacing for condensation. Water on the inside face of the glass is the house’s humidity finding the coldest surface. New windows move the coldest surface somewhere else. Fix the air.
  3. Repairing a rotten frame. Epoxy on a sill that has gone past the first inch is money spent twice.
  4. Replacing one window every year. Each one pays the minimum charge and the measure visit. Group them, worst side first.

Questions people ask

Can fogged windows be fixed without replacing them?

Yes, by replacing the sealed glass unit inside the sash. $250 to $450 a unit in Ontario. The “defogging” services that drill a hole and vent the unit are a cosmetic fix that lasts a year or two; the unit’s insulating gas is already gone either way.

Are drafty windows worth repairing?

Usually. Most drafts are weatherstrip, a lock that no longer compresses the sash, or no foam behind the trim. All three are cheap. A draft through a warped sash is the exception.

Is it worth replacing 20-year-old windows?

Only if they have one of the problems above. Twenty-year-old vinyl casements with sound frames and fresh sealed units are good windows. Twenty-year-old builder-grade sliders with failed seals, flattened weatherstrip and a cracked corner are not.

Should I replace windows before selling?

Replace the ones a buyer or an inspector will write down: fogged, rotten, will not lock. Leave the rest. Buyers pay for a clean inspection; they do not pay $20,000 extra for windows.

Not sure which you have?

Send photos. The $99 window quote review reads the quotes you were given against photos of the windows they want to replace, and says which ones are a glazier’s job. If it is all of them, that is $99 against $20,000.

Review my quotes, $99Price a replacement anyway

Sources and further reading