IGU Replacement Guide: Costs & Fixes for Double‑Pane Windows

Most foggy double-pane windows don't need a full replacement. The real double pane window repair is swapping the failed insulated glass unit, or IGU, while keeping your existing frame. That stops the fog, restores the insulating gas fill, and costs a fraction of a new window. As certified glass technicians serving Dallas and the northern suburbs, we make that call on service calls every week.

You notice the haze between the panes that won't wipe away. You might think the whole window is shot. You're right that something is wrong, but the fix is more direct than you expect. By the end of this guide, you'll know what's inside that foggy glass, why it failed in the Texas heat, what a real repair costs, and how to get it done without replacing the frame.

Key Takeaways- A fogged double-pane window usually needs a new IGU, not a whole new window.- Glass-only IGU replacement often costs $150 to $400 per window, while full window replacement can run $600 to $1,200 or more.- Drill-and-vent defogging removes the moisture but cannot replace the lost insulating argon gas.- Most IGUs fail because a sun-baked seal cracks, letting humid outdoor air inside.- We back every IGU replacement with a lifetime workmanship warranty and a 100% satisfaction guarantee.

What's Really Inside a Double-Pane Window

A double-pane window is a sealed sandwich of two glass sheets with a dry airspace in the middle. The whole assembly is called an insulated glass unit, or IGU. The spacer around the perimeter keeps the panes apart and holds a desiccant, a moisture-absorbing material, that captures any humidity trapped during manufacturing. Before the unit is sealed, the air between the panes is replaced with a slow-moving, non-toxic gas, almost always argon. Argon is denser than regular air, so it cuts heat transfer through the window and boosts the unit's energy efficiency.

When we pull a failed IGU from a Dallas home, the first thing we check is the condition of that perimeter seal. In a working unit, the spacer is dry and the glass is clear. In a failed one, you can see mineral deposits on the inner glass surface and the desiccant is saturated. The gas fill is long gone. That visual check tells us the seal has broken and outside air has been pumping in and out of the unit for months.

Why Double-Pane Windows Fog Up: Seal Failure Explained

Fog between the panes is a seal-failure problem. The IGU's perimeter seal, a butyl or silicone bead, is the only barrier between the dry interior cavity and the humid outdoor air. Over years of North Texas sun, the seal material oxidizes and shrinks. A tiny crack opens, and the window starts to breathe. During the day, the sun heats the glass, the gas inside expands, and a little argon pushes out through the crack. At night, the unit cools, the gas contracts, and the window sucks in damp outdoor air. The desiccant inside the spacer absorbs that moisture until it can't hold any more. Then the moisture condenses on the glass as fog.

We see this most often on west- and south-facing windows, where the afternoon sun beats on the glass for hours. A ten-year-old IGU on a shaded north wall might still be clear, while a six-year-old unit on a full-sun wall is already fogged. The failure is not a defect in the glass. It's a predictable wear item, like tires on a car, and the fix is to replace the worn part, not the whole vehicle.

Can a Fogged Window Be Repaired? The Honest Answer

A fogged IGU cannot be repaired back to factory condition. The seal is broken, the gas is gone, and the desiccant is spent. You can't reseal it, and you can't refill the gas in the field. What you can do is swap the failed glass unit for a new, factory-sealed IGU that fits your existing frame. That is the only permanent double pane window repair. The two shortcuts homeowners sometimes hear about are a temporary defogging treatment and a full window replacement. Here is how they compare.

Why drill-and-vent 'defogging' is only a temporary patch

A defogging service drills two tiny holes in the glass, pumps a cleaning solution between the panes to wash off the mineral haze, vacuums out the liquid, and installs one-way vents. The window looks clear for a while. But the original seal is still broken, so the unit keeps breathing outdoor air. The argon gas is not replaced. The desiccant is still saturated. Within a season or two, the fog returns. We treat defogging as a short-term cosmetic fix, not a repair. You pay a few hundred dollars and still have a failed IGU with zero insulating gas. When a homeowner asks us to make the fog go away and stay away, we recommend glass-only IGU replacement.

Glass-only replacement vs. full window replacement

A glass-only replacement leaves your existing window frame, trim, and interior stops in place. We remove the old IGU, clean the glazing channel, set the new unit on setting blocks, and secure it with a new gasket or glazing bead. The frame is undisturbed, so the interior paint and drywall are untouched. The whole job takes about an hour per window. A full window replacement tears out the entire frame and sash down to the rough opening, which means new interior trim, caulk, and often paint touch-up. It costs two to three times as much and fixes a problem a glass-only swap would have solved. We recommend a full replacement only when the frame itself is rotted, warped, or out of square.

Double Pane Window Repair Costs in Dallas-Fort Worth

Glass-only IGU replacement in the DFW metro area typically runs $150 to $400 per window. The spread comes from a few factors. The size of the unit is the biggest driver: a small bathroom IGU costs less than a large picture window. The glass type matters, too. Clear annealed glass is the least expensive. Low-E coatings, which cut UV and heat gain, add to the cost. Tempered glass, required by code near doors and in bathrooms, costs more than annealed. Argon gas fill is standard in every new IGU we order, so you are not paying extra for it.

Full window replacement, by contrast, starts around $600 per window and can reach $1,200 or more for a standard double-hung unit with Low-E glass and a new frame. The labor is heavier, and the materials include the frame, sash, hardware, and trim. When the frame is sound, the glass-only route saves hundreds of dollars per opening and delivers the same energy performance.

One recent call took us to a 1990s home in Plano with three fogged bedroom windows. The frames were vinyl, tight, and square. We measured the IGUs, ordered the replacements with the same Low-E coating and argon fill, and installed all three in a single morning. The homeowner paid for three glass units, not three new windows, and the bedrooms were clear and energy-efficient again by lunch.

How Our Certified Technicians Replace a Failed IGU

We start by inspecting the sash and frame. If the frame is rotted or the balance system is shot, we tell you before we order glass. Assuming the frame is sound, we measure the visible glass width and height to the nearest sixteenth of an inch, plus the overall unit thickness. That thickness matters, because a 7/8-inch IGU won't fit a frame milled for a 3/4-inch unit. We order the replacement from a Dallas glass fabricator that builds IGUs with dual seals, argon fill, and the same Low-E or tinted glass as the original.

On install day, we protect the floor with a drop cloth, remove the interior stops, and lift out the failed IGU. We clean the glazing channel, set the new unit on rubber setting blocks so it floats in the frame and won't touch the sill, and press a new foam or vinyl gasket into place. The stops go back on, and we check that the sash operates smoothly. The whole process is dustless and takes about an hour. We haul away the old glass and leave the room as we found it. Every IGU replacement carries our lifetime workmanship warranty. If the new unit ever fogs because of our install, we fix it at no charge.

A typical scenario we see in Frisco and McKinney involves a two-story entryway with a large fixed window over the front door. The IGU is heavy and awkward to reach from a ladder. We send a two-person crew with suction cups and a ladder stabilizer. The old unit comes out in one piece, the new one goes in the same way, and the homeowner never has to touch it. The job is done safely from the outside, with no disruption inside the house.

Your Double-Pane Gas Questions, Answered

Do double-pane windows have gas in them?

Yes. Almost every modern double-pane IGU is filled with argon gas during manufacturing. Argon is an inert, non-toxic gas that is denser than air, so it slows heat transfer and improves the window's insulating value. Some high-performance units use krypton gas, which is even denser, but argon is the standard for residential windows. When the seal fails, the argon leaks out and ordinary air takes its place.

Is argon gas dangerous if it leaks?

No. Argon is a naturally occurring gas that makes up a small fraction of the air you breathe. It is colorless, odorless, and chemically inert, so it does not react with anything in your home. A leaking IGU releases argon so slowly you would never notice it, and it poses no health risk to people or pets. The real loss is the window's thermal performance.

Can a lost gas fill be refilled?

Not effectively in the field. Refilling an IGU requires a vacuum-sealed chamber and precise gas concentration controls, equipment only a glass fabricator has. The original seal is already broken, so any gas pumped into the unit would leak out again within days. The only reliable fix is a new, factory-sealed IGU.

How long should a sealed unit last?

A well-made IGU should last 15 to 25 years before the seal fails, but the Texas climate can shorten that window. Intense sun, wide temperature swings, and the constant expansion and contraction of the glass put more stress on the seal than a mild climate does. We see units fail as early as 8 to 12 years on full-sun exposures, while shaded units often last 20 years or more.

Frequently asked questions

How much does a double pane window repair cost? A glass-only IGU replacement in DFW usually costs $150 to $400 per window. The price depends on the size, glass type, and whether the unit needs Low-E or tempered glass. Full window replacement starts around $600 per window.

Can I fix a foggy double-pane window myself? You can't permanently fix a failed IGU as a DIY project. Drilling and cleaning the glass is risky without proper tools and leaves you with a still-broken seal. A replacement IGU must be ordered to exact measurements and installed so it drains and breathes correctly. We recommend a certified technician for a lasting result.

Does homeowners insurance cover a failed window seal? Most standard policies treat seal failure as wear and tear, not sudden accidental damage, and won't cover it. If a storm or a fallen branch broke the glass and the seal, you may have a claim. We advise checking your policy's glass-coverage language before filing.

How long does an IGU replacement take? For a standard double-hung or casement window, the on-site work takes about an hour. The overall timeline, from measurement to install, is usually one to two weeks, which is how long the fabricator needs to build the new IGU.

Get an Honest Assessment of Your Fogged Windows

A fogged double-pane window is a seal-failure problem with a straightforward fix. Before you budget for new windows, let a certified technician check the frame. If the frame is solid, a glass-only IGU replacement clears the fog, restores the argon gas fill, and costs far less than a full tear-out. We serve Dallas, Plano, Frisco, McKinney, and the surrounding areas with free mobile service, so we come to you. For a look at how we price similar glass work, see our guide to rear windshield cost and replacement in DFW.

You might wonder if a glass-only fix will match the rest of your windows. We match the glass type, tint, and Low-E coating to your existing units, so the new IGU blends in. You might worry about the timeline. Most IGUs are ready within two weeks, and the install itself is a one-day job. We stand behind every replacement with a lifetime workmanship warranty and a 100% satisfaction guarantee. When you need a real double pane window repair that lasts, call Glass Replacement Pros at (972) 900-7559 or request a free quote. We'll measure, explain your options, and get the glass ordered.