Do you ever wonder why so many windows fog up? This may not be the first thing you think of on a day-to-day basis, but I’m sure if you have foggy windows or are thinking about replacing your old windows, you have given this some thought. Fog between the window panes is actually the #1 problem in double-pane windows, and it can be fairly easy to prevent. It is caused by the failure of the spacer system that connects the 2 or 3 pieces of glass. Many windows use inferior spacer technology that quickly breaks down. Sometimes in as little as a few years. Once fog appears, the glass unit or the entire window needs to be replaced.
A window that was supposed to last for decades now has a cloudy haze trapped between the panes. It cannot be wiped away. It comes and goes with the weather. And it keeps getting worse.
This is one of the most common window problems in homes across Atlanta, from older neighborhoods in Decatur to newer builds in Johns Creek. Windows that looked perfect at installation now have fog between window panes that will not go away.
The cause is clear. The solution depends on understanding what actually failed.
What Causes Fog Between Window Panes?
Fog between panes is caused by seal failure in the insulated glass unit, and when it comes to insulating glass performance, the spacer system plays a bigger role than many people realize.
Modern windows are built with two or three panes of glass, separated by a sealed air space. That space creates a barrier between the outside and provides increased insulation in double and triple-pane windows.
The panes are held apart by a spacer system, which is sealed to the glass to keep moisture out and insulate Argon gas in. When that seal fails, the performance of the entire window is compromised, and the insulating gas leaks out.
Once the seal breaks, even microscopic gaps allow moisture to get in and become trapped between the panes. The moisture turns into condensation—creating the fog between the window panes. Or the glass gets a rainbow effect, which is the layers of silver in LoE glass being contaminated.
The insulated glass unit, glass, and spacer system cannot be repaired. Once it fails, the only solution is replacing the insulated glass unit, or most times, the entire window.
Why Some Windows Fail Faster Than Others
When evaluating window performance, what people don’t realize is that the insulated glass spacer is probably the most important window component. The edge of the glass is the most vulnerable part of any window, and the spacer system is what is connected to it.
Not all spacers are equal!
Many windows, including high-end companies, are manufactured with Aluminum Space technology. This is often a manufacturing decision, not a cost savings, and many high-end companies use this inferior technology. For decades, aluminum spacers were the industry standard. While durable in structure, they present a significant drawback: they conduct heat extremely well.
Metal spacers create a thermal bridge—a pathway that allows heat to transfer easily through the edge of the glass. And the edge is already the most vulnerable part of the window system. Over time, this movement weakens and eventually breaks the seal.
Metal spacers contribute to a lot of problems.
- Increased heat loss in colder months
- Heat gain in warmer months
- Lower interior glass temperatures at the edges
- Higher likelihood of condensation forming
Over time, these temperature differences create expansion and contraction in the materials, and this movement puts stress on the glass and sealant system, which can eventually lead to seal failure, the #1 problem in double-pane windows.
Inherent problem – Atlanta’s temperature swings, from 95-degree summer days to occasional freezing nights, these immense temperature swings put stress on spacer systems. This constant movement leads to spacer failure and failed windows.
What Is A Better Solution?
SOLUTION – Warm Edge Spacers Improve Performance
Warm edge spacers were developed to address these exact issues. Unlike metal spacers, warm edge systems are made from low-conductivity materials designed to minimize heat transfer. This keeps the edge of the glass warmer in winter and more stable year-round.
GOOD – Duralite® and Duraseal®
1. Improved Energy Efficiency
By reducing heat transfer at the edge of the glass, warm edge spacers improve the overall insulating performance of the window. This leads to better insulation and more consistent indoor temperatures.
2. Less Chance For Seal Failure **This is one of the most important advantages!**
Warm edge spacers like DuraSeal that Windowcrafters manufactures all windows with as STANDARD are designed to be more flexible than rigid metal systems. The seal is not just glued to the glass; it is attached through a lamination process that allows the natural expansion and contraction caused by temperature changes, reducing stress on the seal.
IMPORTANT! Since seal failure is what leads to fog between window panes, reducing that stress directly extends the life of the insulated glass unit in Atlanta Homes.
3. Better Long-Term Durability
Windows are exposed to constant environmental changes—heat, cold, sunlight, and humidity. Warm edge spacer systems are engineered to perform under these real-world conditions, maintaining their integrity over time. DuraSeal attaches to the glass in a completely different way than traditional metal spacers. It is laminated between the 2 pieces of glass, creating a connection that is melded together, not just glued.
4. Enhanced Overall Window Performance
Because they improve both thermal performance and condensation resistance, warm edge spacers contribute to stronger overall window ratings and improved real-life indoor comfort for homeowners.
Why the Spacer System Matters More Than You Think
Once that seal is compromised, moisture enters the airspace, condenses between the panes, and creates the fog between the window panes that homeowners recognize. At that point, the glass unit cannot be repaired—it must be replaced.
That’s why at Windowcrafters we manufacture with DuraSeal. It allows us to manufacture a high-quality window, and it is critical to choose the right spacer system from the start.
Why the Frame Is Rarely the Problem
Many homeowners don’t know why they see fog between the window panes, so they assume the frame has failed. This is never true.
The frame holds the glass unit in place and provides structure. But the seal failure happens inside the glass unit itself, at the spacer, not at the frame.
A vinyl, wood, or metal frame can hold a failed glass unit, and the frame can be perfectly fine, but the window is not fine, because of the faulty seal that has led to fog between the window panes.
How to Spot Early Signs of Seal Failure
Haze That Comes and Goes
Early seal failure often appears as a light haze on humid days that fades when conditions change. This is moisture moving in and out through a weakening seal. If the haze follows weather patterns, the seal is already compromised.
Permanent Clouding or Streaks
Once fog stays visible all the time, the seal has fully failed. At this stage, mineral deposits from the moisture may leave permanent marks on the interior glass surface.
Catching the problem early does not save the seal. But it allows time to plan before the window becomes a larger issue.
Best for: Homeowners checking their current windows for problems.
Rainbow or IlluminationÂ
Once the seal has failed and even microscopic amounts of moisture enter the insulated glass unit, modern LoE glass is contaminated. When anything hits the LoE glass, the layers of silver begin to deteriorate, and this looks like a rainbow. This happens slowly and can start as a single dot or in a corner and then expand over time.
How to Spot Early Signs of Seal Failure
Generally no! You may hear of a company offering defogging services, but this is not a solution and does not work. If by chance it does help, the moisture will just return as the seal has not been fixed, and you’ve spent money on a problem that will come back.
The only solution is replacing the glass unit or getting a new window. If the frame is still in good condition, it may be possible to replace the glass unit, but that depends on a lot of factors. The most important one – can the glass be taken out of the window frame without damaging the frame, and then be put back in? This is possible on windows with a removable glazing bead, and Windowcrafters offers glass repair services for fog between the window panes, if the glazing bead is removable and the IG unit is ½” or wider. If you’d like to look into this service, give us a call or bring your failed window sash to our factory.Â
Some companies specialize in on-site Insulated Glass Unit repair, and this can be a good option, but this is often very expensive!!
If multiple windows are fogging, or your window has more problems and is old, the best bet is to replace your windows. Investing in a new energy-efficient, low-maintenance vinyl window with the correct spacer is most times a better solution than spending money on the old window.
Windowcrafters fabricates insulated glass units at the Tucker, Georgia, facility. Glass replacements can be completed quickly!
What to Look for When Buying Replacement Windows
Traditional metal spacers conduct heat, increase condensation risk, and place more stress on the seal over time. Warm edge spacers are designed to do the opposite—reducing heat transfer, improving durability, and protecting the integrity of the insulated glass unit. And since seal failure is the most common issue in double- and triple-pane windows, the spacer system plays a HUGE role in long-term performance.
That’s why at Windowcrafters we rely on warm-edge spacer technology to produce high-quality windows. It is critical to choose the right spacer system from the start. At Windowcrafters we manufactured using the industry leader – Quanex spacer systems, who have been trusted worldwide for over 35 years, proven in real-world applications and extreme climates.
When shopping for replacement windows in Atlanta, ask these questions:
Ask About the Spacer System
Warm edge spacers outperform aluminum spacers in almost every situation. They handle temperature swings better and last longer. In Atlanta’s climate, this matters more than most homeowners expect.
Ask About the Glass Brand
Cardinal glass is the industry standard for visible light transmission and reduced solar heat gain. Windowcrafters uses Cardinal 270LoE glass in every window. No upcharge. No upgrade fee. Standard.
Ask Who Makes the Glass Unit
Some window companies buy pre-made glass units from third-party suppliers. If something goes wrong, they wait for their supplier to resolve it.
The Windowcrafters 700 Series and 900 Series windows use Cardinal 270 LoE glass with Duraseal warm edge spacers as standard in every window. Because glass units are fabricated in-house, warranty issues and replacements are handled directly, without delays. Homeowners across Sandy Springs, Buckhead, and Marietta have found this makes a difference when service is needed down the road.
What Should You Do Next?
Start thinking about your windows. How many do you have, and do you see any problems starting? If so, and you are ready to explore options, give Windowcrafters a call. We offer wholesale prices to all customers and also have full-service installation for customers looking for a turnkey solution.Â
What causes fog between window panes?
Fog between window panes is caused by seal failure in the insulated glass unit. When the spacer system breaks down, moisture enters the airspace between the panes and becomes trapped, creating condensation or a cloudy haze that cannot be wiped away.
Can foggy windows be repaired?
In most cases, no. Defogging services do not fix the failed seal, so moisture returns. The only real solution is replacing the insulated glass unit or the entire window. Some windows with a removable glazing bead may qualify for glass unit replacement only.
What type of spacer system helps prevent window seal failure?
Warm edge spacers, like the DuraSeal system used by Windowcrafters, reduce heat transfer at the glass edge and flex with temperature changes instead of putting stress on the seal. This makes seal failure less likely over time compared to traditional aluminum spacers.
