If your windows look cloudy, hazy, or foggy between the panes of glass, the most likely cause is a failed seal in the insulated glass unit (IGU). The sealed space inside your double-pane window has allowed moisture to enter, where it condenses on the interior surfaces of the glass.
This is different from condensation on the room side or exterior surface of a window. Fog trapped between the panes cannot be wiped away, and it will not correct itself as the weather changes. In most cases, the long term fix is replacing the glass unit or the entire window.
At Coughlin Windows & Doors, we help homeowners throughout San Diego County and Escondido understand what is happening with their windows and choose a practical replacement solution.
What Causes Foggy Windows Between the Panes?
A modern double-pane window is made with two panes of glass separated by a spacer. The space between the panes is sealed and usually contains air or insulating argon gas. A desiccant, or drying agent, inside the spacer helps absorb small amounts of moisture and keeps the cavity dry.
When the perimeter seal fails, humid outside air enters the space between the panes. Over time, the desiccant becomes saturated. When the temperature of the glass reaches the dew point, the moisture condenses inside the sealed cavity. That trapped moisture creates the fog, haze, streaks, or water droplets you see.
Because the moisture is inside the glass assembly, cleaning the outside of the window will not remove it.
Common causes of window seal failure
Window seal failure can happen for several reasons, including:
- Age and normal material breakdown: Many insulated glass units begin showing problems after 15 to 25 years, although the exact lifespan varies.
- Thermal cycling: Repeated heating and cooling causes the glass, spacer, and sealants to expand and contract.
- Sun and UV exposure: Strong sunlight can degrade sealant materials over time.
- Pressure changes: Temperature swings can create a “thermal pumping” effect that repeatedly pushes air in and out through a weakened seal.
- Manufacturing or installation problems: A defective unit, poor edge sealing, or improper installation can shorten the life of the window.
- Frame movement: Shifting or settling around the opening can place stress on the glass and seal.
- Water intrusion: Poor drainage or deteriorated sealant around the frame can accelerate the problem.
San Diego’s climate can expose windows to several of these stressors. Coastal homes may experience salt air and humidity, while homes in Escondido, Poway, and Rancho Bernardo can experience hot inland afternoons followed by cooler nights. Strong year-round UV exposure adds another source of stress.
Is the Fog Between the Panes or on the Surface?
Before deciding what to do, identify exactly where the condensation is located. This simple distinction helps separate a failed window seal from a normal humidity or weather condition.
Fog or moisture between the panes
If you cannot wipe away the haze from either side of the glass, the insulated glass unit has likely failed. The sealed cavity has been compromised, and the glass unit needs to be replaced.
Condensation on the room-side surface
If moisture is on the glass facing the inside of your home, the window seal may be working properly. The issue may instead be high indoor humidity caused by:
- Cooking
- Showers and baths
- Laundry
- Poor bathroom ventilation
- Drying clothes indoors
- Limited airflow around the window
Using exhaust fans, improving ventilation, and controlling indoor humidity may help. Persistent room-side condensation, however, can still deserve professional evaluation if it is damaging the sill or surrounding finishes.
Condensation on the exterior surface
Condensation on the outside of the glass is often normal, particularly in the morning or during weather conditions when the exterior glass is cooler than the surrounding air. Exterior dew does not necessarily indicate a defective window. In fact, it can occur on an energy-efficient window because less indoor heat is reaching the outside pane.
Why a Failed Seal Matters
Foggy double-pane windows are more than a cosmetic concern. When the seal fails, the window may lose some of the performance it had when it was new.
Lost insulation
Insulated glass units are designed to slow heat transfer. If argon gas escapes and outside air enters, the space between the panes may no longer provide the same insulating performance.
Higher cooling costs
A failed window may allow more heat to pass through the glass. During warm San Diego weather, that can make rooms less comfortable and cause your air conditioner to work harder.
Permanent staining and haze
Moisture trapped inside the unit can leave streaks, mineral deposits, and cloudy areas that become increasingly difficult to see through.
Damage around the window
Long-term moisture can contribute to deterioration around the sill, frame, trim, or nearby drywall. If you see water stains, soft wood, peeling paint, or discoloration, the problem may involve more than the glass itself.
Lower curb appeal
Fogged windows are noticeable from both inside and outside. They can make a home look older and may be a concern to prospective buyers or home inspectors.
Can Foggy Windows Be Repaired?
A foggy insulated glass unit cannot be restored by wiping, cleaning, or using a household product. The moisture is sealed inside the glass assembly.
Some companies offer “defogging” services that involve drilling small holes, drying the cavity, and installing vents. This may temporarily improve the appearance, but it does not restore the original airtight seal, Low-E performance, or argon gas fill. In many cases, the unit fogs again.
The dependable options are:
- Replace the insulated glass unit only: This may be appropriate when the existing frame is in good condition and the rest of the window operates properly.
- Replace the entire window: This is often the better choice when the window is older or has additional problems such as drafts, difficult operation, damaged frames, or poor energy performance.
Coughlin Windows & Doors does not repair windows or doors that were not originally installed by Coughlin. For customers who need glass or screen service on an existing window, we can refer you to Stuart’s Glass & Screen at (760) 745-7963. For windows installed by Coughlin, our team stands behind our installation and warranty commitments.
When Should You Replace the Entire Window?
Glass-only replacement may make sense when the frame is structurally sound and the failed seal is the only issue. Full window replacement is usually worth considering when:
- Several windows have failed seals
- The windows are approximately 15 to 25 years old or older
- Frames are cracked, rotted, warped, or corroded
- Windows are difficult to open, close, or lock
- You feel drafts around the frame
- Energy bills have increased
- You are already planning other home improvements
- You want to improve comfort, UV protection, or curb appeal before selling
During a consultation, we can evaluate the condition of the existing frames and help you determine which windows actually need replacement. Replacing every window is not always necessary.
Coughlin offers a wide selection of window styles, including single-hung, double-hung, picture, casement, awning, bay, bow, and double-pane windows.
Why Glass and Installation Quality Matter
Replacing a foggy window is an opportunity to address both the failed glass and the factors that may have contributed to premature failure.
Coughlin Windows & Doors partners with Simonton, Milgard, and Andersen Windows. One available option is the Simonton DaylightMax™ vinyl replacement window, which includes double-strength dual-pane glass, ProSolar® Shade Low-E3 coatings, argon gas insulation, and UV protection. These features help reduce heat transfer, protect furnishings from fading, and improve comfort.
Installation matters just as much as the product. Accurate measurements, proper flashing, weather-resistant sealants, drainage, and a secure fit help protect the opening from water intrusion and air leakage. Our San Diego window replacement service includes careful removal, frame preparation, installation, sealing, and a final operating check.
How Much Does It Cost to Replace Foggy Windows in San Diego?
The cost depends on whether you need a glass-only replacement or a complete window replacement. It also depends on the window’s size, style, material, glass package, frame condition, and installation requirements.
As a general guide, mid-grade vinyl replacement windows installed in an existing frame commonly range from approximately $600 to $1,000 per window in the San Diego area. Your project may be higher or lower depending on the details.
Coughlin provides 100% free estimates and offers flexible financing options, including low-interest and zero-percent introductory rate plans for qualified customers. A consultation gives you a more accurate price without requiring you to guess based on a general range.
What to Expect From a Coughlin Consultation
A free consultation may include:
- An evaluation of the fogging and the existing window frames
- A discussion of whether glass-only or full replacement makes more sense
- Measurements of the openings
- Recommendations for window styles, materials, and glass options
- An explanation of installation details and warranty coverage
- Financing information and a written estimate
Coughlin Windows & Doors has more than 30 years of industry experience, over 500 happy clients, and a 4.9 Google rating based on 104 reviews. Our team is fully licensed, bonded, and insured, including liability and workers’ compensation coverage.
We provide Energy Star-rated products, a lifetime warranty on installations and replacements, and accidental glass breakage coverage. You can also visit our showroom to compare products in person:
Coughlin Windows & Doors
215 W Washington Ave.
Escondido, CA 92025
(760) 737-5000
Get Help With Foggy Windows in San Diego or Escondido
Fog between the panes usually means the sealed insulated glass unit has failed. It is not a cleaning problem, and it will not go away on its own. Depending on the age and condition of your windows, replacing the glass unit may be enough, or a full window replacement may provide better long-term value.
If you are seeing foggy windows, drafts, difficult operation, or damaged frames, contact Coughlin Windows & Doors for a free estimate. Call (760) 737-5000 or visit our Escondido showroom to discuss your options.
We serve homeowners in San Diego, Escondido, San Marcos, Vista, Rancho Bernardo, Poway, Scripps Ranch, Mira Mesa, Carmel Valley, Rancho Peñasquitos, Valley Center, Lemon Grove, and surrounding San Diego County communities.
Frequently Asked Questions
Why are my windows foggy between the panes?
Fog between the panes usually means the seal on the insulated glass unit has failed. Moisture has entered the sealed cavity and is condensing on the inside surfaces of the glass. The glass unit or the entire window typically needs to be replaced.
Can foggy windows be repaired?
A foggy window cannot be cleaned between the panes without taking apart or altering the sealed glass unit. Defogging may temporarily improve the appearance, but it does not restore the original seal, insulating gas, or Low-E performance. Replacing the glass unit or window is the more reliable solution.
Is foggy window glass a sign I need new windows?
Not necessarily. If the frame is in good condition and the window operates properly, replacing the insulated glass unit may be possible. Full replacement is more appropriate when the window is older or also has drafts, damaged frames, difficult operation, or poor energy performance.
Does window fogging mean a broken seal?
In most cases, yes. Fog, haze, or water droplets that appear between the panes indicate that the sealed insulating cavity has been compromised.
Why do windows fog only in the summer or winter?
Temperature changes cause moisture inside a failed insulated glass unit to reach its dew point. This can make the fog appear or become more noticeable during certain seasons. Condensation on the room-side surface, however, is more often related to indoor humidity.
What does it cost to replace San Diego windows?
Mid-grade vinyl replacement windows installed in an existing frame commonly cost approximately $600 to $1,000 per window, although the final price depends on size, style, glass, materials, and installation requirements. Coughlin provides free estimates and financing options for qualified customers.
