Do I Have To Replace Fogged Window Glass?

Seeing fog, haze, or condensation on your window glass can make you wonder if the whole window needs to be replaced. 

The good news is that you may not need to replace the entire window.

In many cases, you can replace the glass unit instead of replacing the entire window. That can save you money and leave the existing frame in place.

In this post, we’ll go over everything you need to know about replacing fogged window glass.

Do You Need To Replace Fogged Window Glass?

You only need to replace fogged glass if the mist is trapped between the panes. 

If that is the case, the insulated glass unit may have lost its seal. Once that happens, moisture can enter the space between the panes, creating the cloudy or fogged appearance you see.

You usually cannot fix that by wiping the glass. The moisture is inside the sealed unit.

However, you may be able to replace just the insulated glass unit, often called an IGU. 

The existing window frame can stay in place if it is still in good condition.

If the fog sits on the inside of the room, your glass is totally fine. It’s just humidity from hot showers or cooking; running an exhaust fan or a dehumidifier clears it right up.

When Should You Replace Fogged Window Glass?

If the fog is trapped between the panes, replacing the glass unit is usually worth considering. 

A failed seal can reduce the insulating performance of the window, and the cloudy appearance can become more noticeable over time.

You should also consider replacement if the glass is cracked, damaged, or difficult to see through.

Here are a few signs that it’s time to have the window checked include:

• Persistent fog or moisture between the panes
• Cracked or damaged glass
• Noticeable drafts around the window
• Difficulty opening, closing, or locking the window
• Condensation that keeps returning despite reasonable indoor humidity

You don’t necessarily have to make the decision on your own. A window professional can inspect the glass and frame and explain your repair options.

Also Read: Window Glass Replacement Cost

How To Replace Fogged Window Glass

Replacing an insulated glass unit requires care because the glass can be heavy, sharp, and difficult to handle. The exact process also depends on the window design.

If you’re experienced with window repairs, the general process looks like this:

#1 Remove The Window Sash

If you have a double-hung or sliding window, you can take the moving section (the sash) completely out of the frame. 

Unlock the window, lift it slightly, and tilt the top toward you to release it from the side tracks and spring balances. 

Carry the sash over to a flat table or a pair of sawhorses covered in an old blanket so you have a comfortable, protected workspace.

If you’re dealing with a fixed picture window, you’ll have to work standing up, but operable windows are infinitely easier to handle flat on a table.

#2 Pry Off The Glazing Stops

Take a look around the perimeter of the glass on the face of the sash. 

You will spot thin plastic, wood, or vinyl strips snapped into channels around the edge. These are your glazing stops. 

Slide a stiff putty knife into the thin seam near the center of a strip, then pry gently away from the glass until the strip pops loose. Work around all four edges, removing the sides first, and set them aside in order so you remember which piece fits where.

#3 Cut The Adhesive And Remove The Glass

Even with the stops removed, the glass unit won’t just fall into your hands because a strip of sticky, double-sided foam tape glues it to the back frame lip. 

Also Read: How To Remove Your Window Sash

Put on a pair of sturdy work gloves, take a sharp utility knife, and carefully slice through that adhesive layer all the way around the frame. 

Once the tape is cut through, gently push the old glass unit free.

Carry the old glass straight out to the garage or trash area where nobody can step on it.

#4 Measure And Order The Replacement IGU

Do not guess these numbers, because custom-made glass units cannot be trimmed down with a saw if they end up an eighth of an inch too big. 

Measure the open pocket of the sash from top to bottom and side to side in two different spots, taking the smallest reading and subtracting a quarter-inch from both the height and width to leave room for expansion. 

Next, measure the overall thickness of the old unit, which usually sits somewhere between half an inch and three-quarters of an inch. 

Call a local glass shop, hand over those exact numbers, let them know you need a sealed double-pane IGU.

#5 Clean The Sash And Apply New Glazing Tape

While you wait for your new glass to arrive, grab a scraper and clean out every scrap of old adhesive and grime left in the frame channel.

Wipe down the plastic or wood with a little rubbing alcohol to give yourself a pristine, grease-free surface. 

Once the area dries completely, unroll fresh double-sided glazing tape and press it firmly along the perimeter of the frame rebate.

Also Read: How To Get Rid Of Mold In Double Pane Windows

#6 Set The New Glass Unit

Place two small rubber or plastic setting blocks along the bottom channel to hold the glass slightly off the frame base. 

Peel the backing paper off your fresh glazing tape. 

Carefully rest the bottom edge of your new glass onto those setting blocks, double-check that it is centered horizontally, and gently tip the pane backward until it bonds snugly against the sticky tape.

#7 Reinstall Glazing Stops

Take the glazing stops you set aside earlier and snap them back into place, starting with the ends and pressing toward the center. 

A light tap with a rubber mallet helps seat the barbs deep into their retaining channels.

Once all four strips click in flush against the new glass, pop the sash back into your window frame, test the lock, and you are all done.

Bottom Line

Fogged window glass does not always mean you need to replace the entire window.

If the fog is between the panes, the insulated glass unit has likely lost its seal, and replacing the IGU may solve the problem. You can often keep the existing frame if it’s still in good shape.

Fog on the inside or outside of the window can have completely different causes, including indoor humidity and outdoor condensation.