Foggy Window Repair in Madison, WI

What fog between the panes means: the seal of the insulated glass unit has failed

Fog between the panes means the seal of the insulated glass unit has failed and moist air got in. When the seal breaks, the gas leaks out and outside air gets in. The moisture in that air condenses between the panes. You see fog or a cloudy film between the panes that wiping does not remove (This Old House).

StructureTech, a Minnesota home inspection firm, describes how it plays out. At the edge of the unit, a desiccant (a drying material) holds moisture for a while, so a window can look normal in the early stage. Later, a quick outdoor temperature change can bring a small patch of fog between the panes that goes away again. Repeated drying leaves a thin mineral layer, and the glass then looks permanently dirty. The same firm says inspectors often cannot see a failed seal, especially with screens in place or dirty glass, so check each window yourself. It calls fogged glass mostly cosmetic and not a critical repair item; that is one inspector's opinion.

How a double-pane unit is built: two panes, a spacer, sealant, sometimes argon or krypton gas

The sealed unit is the glass part of the window, with a sealed space between the panes that holds insulating gas (This Old House). The Efficient Windows Collaborative glossary describes it as glazing "hermetically sealed to form a single glazed unit with one or more air spaces in between." Its parts:

• Panes: two in a double-pane unit, three in a triple-pane one. This Old House adds tinted or reflective glass, which cuts glare and solar heat.
• Spacer: placed between the panes to keep them apart (Efficient Windows Collaborative; U.S. Department of Energy).
• Sealant: the compressible plastic material that seals the junction of the parts (Efficient Windows Collaborative). When this seal breaks, fog appears (This Old House).
• Desiccant: a material that absorbs moisture from the sealed air space (Efficient Windows Collaborative).
• Gas fill: argon or krypton, both inert and nontoxic, placed between the panes to cut heat transfer (Efficient Windows Collaborative).

Have the quote name the glass in the new unit, so you can compare quotes like with like.

Warning signs: condensation or a cloudy film between the panes

Look for condensation between the panes, or glass that looks permanently dirty. StructureTech describes a short-lived fog after a sudden outdoor temperature change, and later a thin mineral layer. These signs alone do not prove a bad seal, so use the wipe test below as the deciding step.

Sources describe condensation or a cloudy look between the panes (This Old House; StructureTech). We found no source that links drafts or sharp indoor temperature swings to a failed seal, so treat them as questions to ask the company, not as signs.

Fog inside vs on the room side vs outside: which one is a failed seal and which is just humidity

Fog inside the unit, between the panes, is the failed seal. Fog on the room side or outside is just surface condensation, which a cloth can wipe away.

Try this before you call anyone. Do it when the fog is showing.

1. Wipe the room side of the glass with a dry cloth. If the fog clears, it was surface condensation. The seal is not the problem.
2. Wipe the outside. Fog that wipes off outdoors is surface condensation, also not a seal problem.
3. If both faces are clean and the haze stays, the seal has likely failed. This Old House also ties fog between the panes, as opposed to surface condensation, to a failed seal.

Foggy window repair, defogging or a new window: which fits

Three different jobs get sold under the heading of foggy window repair. Ask which one a price covers before you compare quotes.

Replacing only the sealed unit in the existing sash vs replacing the whole window

Replacing only the sealed unit (IGU replacement) is the lighter job; replacing the whole window is the larger one. This Old House notes that not every shop does unit swaps, so ask on the first call. You may see the job called insulated glass replacement, IGU replacement, sealed unit replacement or foggy window glass replacement.

Defogging or "seal repair" vs a new unit: what each does and doesn't fix

Defogging clears the view but does not rebuild the seal. According to This Old House, the steps are to drill, flush, dry and seal the unit, and the result is cosmetic: it does not restore the seal or the gas. No national price for defogging was found, so none is shown here. If a company offers window seal repair or double pane window seal repair, ask whether that means a new unit or a defog, and get the answer in writing.

StructureTech names three options: replace the whole window, replace only the sash, or replace only the insulated glass unit; ask the company which fits and what each costs.

New sash or whole new window

A unit swap keeps your sash (This Old House), so ask the company to check the sash and frame and to say in writing whether the glass unit alone is enough. Read about window sash and frame repair before you decide on full replacement. Madison's permit chart lists window and frame replacement as permit-required, so ask Building Inspection before a full swap (see the permit section below).

Foggy window repair cost

These are national figures, not Madison quotes. No Madison company price for this work was found, and no local price is estimated here. The source is This Old House, which uses Angi cost data. The page is dated June 23, 2026 and was read on October 23, 2026.

The source gives no figure for exactly four units. Read the table as national ranges for the whole job. Your quote may be higher or lower.

A second signal sits well above those numbers. In a June 2026 update, StructureTech (a Minnesota home inspection firm) says a small window's sealed unit costs at least $250 and most run $300 to $700, with larger windows costing more. This is one Upper Midwest inspector's market signal, not Madison pricing and not a quote. The two sources differ widely, so treat both as signals and get Madison quotes in writing.

Cost by unit size and glass type, and for several windows at once

What moves the price is the unit size, the glass type and how many windows you do at once.

• Number of units: the job totals above rise with the count.
• Size, spacer type, grids, tempered glass and height above ground: StructureTech names these as the price movers. It gives no figure for any single one, and we found no sourced price per glass type (plain, Low-E, gas-filled, tempered or triple-pane), so the table above has no such row. Tempered glass is the type that breaks into small dull pieces and is widely used as safety glass (Glass Doctor); ask whether your window needs it.
• Sash work: check whether the quote includes any. See window glass replacement for glass jobs that are about a crack or a break, not fog.
• Unit swap or defog: the two jobs differ in what they do, so their prices are not comparable.

Ordering lead time and the visit: measure, order, install

Sources describe three parts of a unit swap. The unit is measured. A custom unit is ordered; an EngineerFix guide for vinyl windows says to record the smallest of three width and three height measurements, plus the thickness. Then the old unit comes out and the new one goes into your existing sash (This Old House). Use these asks to prepare:

• When you send the form or call, say how many windows are fogged, which rooms they are in and whether any sash sticks or looks rotted.
• Ask for a written quote that names the glass type and says whether the price is for a new unit or a defog.

On timing, EngineerFix says the lead time for a custom sealed unit is typically one to three weeks. A Minnesota inspector (StructureTech) reports that the glass for the author's windows was ready in about two weeks after on-site measurements, from a local manufacturer. Neither is a Madison supplier, so ask your company for its own lead time. One Denver glass company says minor repairs take one to two hours and jobs that need a new sealed unit take several days; that is one company's summary. No source times the swap itself.

How to compare foggy window repair quotes

Ask every company the same questions so the quotes line up:

• Is the price for a new sealed unit or for defogging?
• What glass is in the new unit: plain, Low-E, gas-filled, triple-pane?
• Who orders the unit and how long does the order take?
• What happens if the sash is found rotted when the old unit comes out?
• What coverage comes with the new unit, and is it written down?
• If the house was built before 1978, how will the company handle the lead-safe rules?

Wisconsin's consumer protection agency (DATCP) says a written contract should list the company name and address, a full job description, the total price and the start and completion dates. For a contract over $25 signed at home, Wisconsin gives three business days to cancel. To start, send the quote form on this page or contact Madison Window Repair, and we connect you with a local company.

Manufacturer glass warranties: check the spacer stamp or label before paying

Before you pay for a new unit, check whether the old one is still covered. StructureTech says most window makers give a 20-year warranty on the glass units and that it does not cover labor. The Efficient Windows Collaborative says failure coverage of 10 to 20 years is common (page undated). StructureTech adds that when a seal is covered, the maker can usually supply a replacement sash after a phone call with the window's serial numbers. So find the paperwork and the serial numbers from when the windows were bought or installed.

Marvin says its units carry a year mark. Your paperwork and the maker's terms decide whether coverage still applies. Here is what Marvin says, as one example:

• Marvin, made before November 2003: Marvin says the silver spacer bar carries an engraving with the Marvin name, and the last two digits identify the year of manufacture. It can sit anywhere around the glass edge. Some plants from 2000 to 2003 used a clear label at the bottom of the glass instead.
• Marvin, made after November 2003: Marvin says to look at the interior glass surface in the corner of the sash or door panel for a laser-etched code. The plant year is in the code, labeled "Glass manufacturer-Plant Year."

If your window is another brand, ask the maker of your window how its units are labelled and where the mark sits. If a company offers its own coverage on a new unit, get the length, the limits and who pays labor in writing.

Permits and historic districts in Madison

Madison's permit chart lists "Windows & Frames - replace" as permit-required work. The chart has no row for glass-only replacement and no notes column, so it does not say a glass-only swap is exempt. The chart tells readers to contact Zoning staff for clarification. The city's storm-damage page says no permit is needed for small repairs under $500 in estimated value. No Madison rule on a sealed-unit swap was found, so ask Zoning staff and Building Inspection before you order.

Madison also has five local historic districts: First Settlement, Mansion Hill, Marquette Bungalows, Third Lake Ridge and University Heights. In them, the Landmarks Commission must approve exterior changes on designated properties, and the city asks owners to apply before applying for a building permit. The city's standards (an undated PDF) say a historic single-glazed sash may be modified to take insulated glass when that will not jeopardize the sash or significantly alter the window's appearance. If your home is in one of these districts, contact the Preservation Planner before you order anything.

Older painted sashes: lead-safe questions

If your home was built before 1978, the window parts may carry old paint, and Wisconsin's lead-safe rule applies to homes of that age. The EPA says replacing a pane or fixing a balancer is not window replacement, but the job can still be covered if it disturbs more than 6 square feet of painted surface per room. The EPA also notes that the glazing holding older panes is typically painted. A complete window replacement in a pre-1978 home is always covered, whatever the size.

EPA's rule for a pane job turns on paint disturbed. Whether the company treats a sealed-unit swap as covered is a question for the company, so ask it. The Wisconsin Department of Health Services tells owners to check its list of certified lead companies, confirm the worker is a certified Lead-Safe Renovator, get a written contract and ask for the EPA Renovate Right pamphlet. It also suggests asking how the company will contain dust and verify the cleanup.

Energy and comfort after replacement: Low-E coatings, gas fill and spacers

A new sealed unit gives you a chance to choose how it performs. These are the choices you may hear about:

• Low-E coating: a coating that blocks radiant energy but lets visible light through (U.S. Department of Energy). The Efficient Windows Collaborative notes that moisture inside a failed unit can degrade these coatings.
• Gas fill: the insulating gas between the panes, which is what leaks out when a seal fails (This Old House). Ask whether the new unit is gas-filled.
• Spacer: the Efficient Windows Collaborative (EWC) says spacers sit between the panes of a double- or triple-glazed window, and the U.S. Department of Energy (DOE) says insulating spacers keep the panes apart. The EWC glossary lists warm-edge spacers as low-conductance spacers that reduce heat transfer near the edge of the glass; we have no sourced price or comfort figure for them, so ask the company which spacer is in the quote.
• Triple-pane units: DOE says high-performance windows use two or three glass panes. This Old House describes a triple-pane unit as three panes with two gas-filled spaces, against one gas-filled space in a double-pane unit. We found no stored source on whether a triple-pane unit fits a double-pane sash, or on what it costs to replace one. Ask the company and the window maker.

No energy savings figure is given on this page because none was found from a source that can be checked. Ask each company to name the glass type in the quote so you can compare like with like.

Why seals fail and how long they last

Tried and True Glass, a Denver company, lists age, extreme temperatures, poor installation and pressure changes at higher elevations like Denver's among the causes. It advises against pressure washing and slamming window frames shut. That list comes from a company, not a test lab, so treat it as a guide.

No year figure for seal life from an official or trade source was found, so this page does not give one. The Efficient Windows Collaborative says well-made units lose under 1 percent of their gas a year. The 10 to 20 year coverage period it calls common is a term set by the maker, not a measure of how long a seal lasts (see the warranty section).

Frequently asked questions about foggy window repair

Sources

• This Old House, window repair cost (Angi data, June 23, 2026)
• This Old House, fogged window repair
• This Old House, window glazing
• StructureTech, repairing a window with fogged glass (2026 update)
• StructureTech, failed window seals
• EngineerFix, replacing double-pane glass in a vinyl window
• U.S. Department of Energy, high-performance window glass
• Glass Doctor, types of window glass
• Efficient Windows Collaborative, durability of insulating glass
• Tried and True Glass, window repair
• US EPA, window repair under the RRP rule
• US EPA, Renovation, Repair and Painting Program
• Wisconsin DHS, lead-safe renovation rule
• Wisconsin DHS, hire a lead-safe contractor
• City of Madison, permits chart
• Efficient Windows Collaborative, glossary
• Marvin, identify my product
• City of Madison Building Inspection, storm damage
• City of Madison, historic preservation
• City of Madison, historic districts standards (undated PDF)
• Wisconsin DATCP, home improvement consumer tips

Related services

If the glass is cracked or broken instead of foggy, see window glass replacement. If the sash, sill or frame is damaged, see window sash and frame repair. For questions about a specific window, contact Madison Window Repair.