What Are Blown Double Glazed Windows — and What Should You Do?
Blown double glazed windows occur when the airtight seal between two panes of glass fails, allowing moisture to enter and become permanently trapped inside the unit.
Here’s a quick summary of what you need to know:
| Question | Quick Answer |
|---|---|
| What does “blown” mean? | The seal between the two glass panes has failed |
| Main sign | Foggy or misty glass you can’t wipe away |
| Main cause | Age, poor installation, or thermal stress |
| Can it be repaired? | The unit needs to be replaced — not repaired |
| Cost to fix | Typically $60–$400 to replace the glass unit only |
| Ignore it? | No — it raises energy bills and risks mold |
If you’ve noticed a persistent cloudy or foggy patch inside your window that won’t wipe off, your window seal has likely failed. This is one of the most common window problems homeowners face — and in Colorado Springs, the combination of high altitude, intense UV exposure, and dramatic temperature swings makes it even more likely.
The good news? In most cases, you don’t need to replace the entire window. Replacing just the sealed glass unit is usually enough to restore performance and comfort.
I’m Michael Smith, owner of Complete Window Care, and with over 18 years of hands-on experience diagnosing and resolving window issues — including countless blown double glazed windows — across Colorado Springs and the Front Range, I’ve seen how quickly a failed seal can affect a home’s comfort and energy costs. In this guide, I’ll walk you through exactly why it happens and what your best options are.
Understanding Blown Double Glazed Windows
To understand why a window “blows,” you first have to understand how it’s built. Modern windows aren’t just two sheets of glass slapped together. They are precision-engineered components known as insulated glass units, or IGUs.
An IGU consists of two (or sometimes three) panes of glass separated by a spacer bar. This spacer bar creates a gap that is typically filled with an insulating gas, such as argon gas, which is much denser than air and significantly slows down heat transfer. To keep the inside of the unit bone-dry, the spacer bar is filled with desiccant beads — tiny pellets that act like those “Do Not Eat” silica packets you find in shoeboxes, absorbing any trace amounts of moisture.
The entire unit is held together by a high-grade hermetic seal. When this seal is intact, the window provides excellent thermal insulation and clear views. However, when that seal breaks, the insulating gas escapes, and moist air from the Colorado Springs atmosphere rushes in. Once that moisture enters, it eventually saturates the desiccant beads. When the beads can’t hold any more water, the moisture condenses on the glass, and you get that classic “blown” look.
If you are curious about how these compare to older styles, our guide to single-pane and double-pane glass explains the difference in plain terms.
Identifying Blown Double Glazing Symptoms
How do you know for sure if your windows are blown? It isn’t always a dramatic crack or a loud pop. Often, the signs are subtle at first:
- Internal Misting: This is the smoking gun. If you see fog, mist, or actual water droplets between the panes of glass that you cannot wipe away from either the inside or the outside, the seal is gone.
- Cloudy or “Milky” Glass: Over time, the minerals in the trapped evaporated water can leave a permanent residue on the inside of the glass, making it look dirty even after a fresh cleaning.
- Visible Water Pooling: In severe cases, you might actually see water sitting at the bottom of the window, resting on the spacer bar inside the unit.
- White Dust: If you see a fine white powder inside the glass, it’s a sign that the desiccant beads have physically broken down due to extreme moisture saturation.
For a deeper dive into these warning signs, check out our guide to spotting a broken window seal.
Distinguishing Between Internal and External Condensation
Before you panic and call for a replacement, it is important to check where the moisture is. Not all condensation means your windows are failing.
- Room-Side Condensation: This happens on the surface of the glass inside your home. It’s usually caused by high humidity (cooking, showering, or even just breathing) hitting a cold surface. This is a ventilation issue, not a window failure.
- External Condensation: Believe it or not, seeing dew on the outside of your windows in the morning is actually a sign that your windows are working perfectly! It means the heat is staying inside your house and not warming up the outer pane of glass.
- Inter-pane Condensation: If the moisture is between the two sheets of glass, that is blown double glazed windows.
Our article on foggy or cloudy window panes can also help you determine if you need a glazier or just a dehumidifier.
Why Window Seals Fail: The Science of Solar Pumping
You might be wondering, “My windows were fine yesterday, what changed?” The most common culprit is a process called solar pumping.
Every day, the sun hits your windows, causing the air or gas inside the IGU to heat up and expand. This puts pressure on the seals. At night, the temperature drops, the gas contracts, and the pressure reverses. This constant “breathing” or pumping action eventually stresses the sealant to the point of failure. Over 15 to 20 years, even the best seals can succumb to this mechanical fatigue.
Other factors include:
- UV Degradation: Intense sunlight can eventually dry out and crack the rubberized sealants used around the glass.
- Failed Desiccant: If the moisture-absorbing beads become saturated too quickly, they can expand and put internal pressure on the seal.
- Chemical Damage: Using harsh, solvent-based cleaners can actually eat away at the perimeter seals over time.
Environmental Factors in Colorado Springs
In April 2026, we are still seeing the same challenges that have always plagued Pikes Peak region homeowners. Colorado Springs is a “perfect storm” for blown double glazed windows.
- High Altitude: The atmospheric pressure at 6,035 feet is lower than at sea level. If a window unit was manufactured at sea level and shipped here without “capillary tubes” to equalize pressure, the internal pressure can cause the glass to bow outward and the seals to pop.
- Extreme Temperature Swings: We often see 40-degree temperature shifts in a single day. This accelerates the solar pumping process dramatically.
- Intense UV: Our thinner atmosphere means the sun’s rays are much more punishing on the materials that hold your windows together.
If you’re dealing with these local challenges, our guide to window seal leaks and condensation covers what to look for next.
Manufacturing and Installation Issues
Sometimes, the window is doomed before it even reaches your house. Poor manufacturing can leave “voids” in the sealant. Furthermore, if the window frame doesn’t have proper drainage, water can pool around the bottom of the glass unit. If the edge of the IGU sits in standing water for long periods, the sealant will eventually “saponify” (turn to mush) and fail. This is why professional installation and frame maintenance are so critical.
The Impact of Ignoring Failed Window Seals
It’s tempting to look at a misty window and think, “I’ll get to it next year.” But a blown window is more than just an eyesore; it’s a functional failure.
Energy Efficiency & Heat Loss: Double glazing is designed to reduce condensation by up to 85% and keep your home insulated. Once the seal is blown and the argon gas is gone, your window’s R-value (insulating power) plummets. It’s essentially like having a very expensive single-pane window. In the winter, you’ll feel cold draughts, and in the summer, the heat will pour in, causing your energy bills to spike.
If rising heating costs are already on your mind, this guide on using insulated glass to save energy explains why the glass unit matters so much.
Health Risks: Trapped moisture is a breeding ground for mold and dampness. While the mold might start between the panes, the reduced insulation causes the inner pane to stay colder, which encourages mold growth on the inside of your window frames and walls. This can lead to respiratory issues and allergic reactions for your family.
Loss of Acoustic Insulation
One of the “hidden” benefits of double glazing is noise reduction. The gas-filled gap acts as a buffer against street noise and barking dogs. When the seal fails and the gas is replaced by moisture-laden air, you’ll likely notice that your home feels much noisier than it used to. Restoring that peace and quiet often requires professional glass replacement.
Structural Risks to Window Frames
If moisture is allowed to sit inside the window unit, it can eventually migrate to the window frame itself.
- Timber Frames: Moisture leads to wood rot, which can eventually require a total (and expensive) window replacement.
- uPVC/Vinyl Frames: While they don’t rot, constant moisture and temperature fluctuations can cause the frames to warp or the internal hardware to rust and seize up.
Catching the problem early is key. Our guide to signs you may need replacement glass can help you see whether your frames are still salvageable.
Solutions for Blown Double Glazed Windows: Repair or Replace?
When a window blows, you have three main paths. At Complete Window Care, we always advocate for the most cost-effective solution that actually works.
| Option | Typical Cost | Best For… | Longevity |
|---|---|---|---|
| Full Window Replacement | $200 – $1,200+ | Damaged frames or style upgrades | 20+ years |
| Glass-Only Replacement | $50 – $400 | Blown seals with healthy frames | 15-20 years |
| DIY Defogging Kits | $30 – $80 | Temporary cosmetic fix only | Weeks to months |
As you can see, replacing just the glass is often the “sweet spot” for homeowners. If you’re deciding between the two, this breakdown of glass-only versus whole-window replacement can help.
When to Choose Glass-Only Replacement for Blown Double Glazing
If your window frames are in good condition—meaning they aren’t rotted, warped, or cracked—there is absolutely no reason to tear them out of your walls. Replacing the sealed glass unit (the IGU) is a surgical procedure. We remove the beads, take out the old failed glass, and drop in a brand-new, factory-sealed unit.
This process usually takes less than an hour per window and saves you up to 70% compared to a full window replacement. It’s eco-friendly, too, as the old glass can often be recycled rather than ending up in a landfill. For residents in our area, our Colorado Springs glass replacement service restores your home’s efficiency without the mess of a full remodel.
The Limitations of DIY Defogging Kits
You might see “defogging” kits online that involve drilling tiny holes in the glass to vent the moisture. While these might make the window look clear for a short time, they are not a repair.
- No Insulation: Drilling a hole means you can never have insulating gas (argon) inside again.
- Temporary: The moisture will eventually return because the seal is still broken.
- Warranty: Most of these kits will immediately void any remaining manufacturer warranty on your windows.
- Precision: It is incredibly easy to shatter the tempered glass found in most modern windows if you don’t know exactly what you’re doing.
Preventing Future Double Glazing Failure
While no window lasts forever (most quality units have a lifespan of 15 to 25 years), there are ways to make sure you get the most out of your investment.
- Warm Edge Spacers: When you replace your blown glass, ask for “Warm Edge” spacer bars. Unlike old-fashioned aluminum spacers, these are made of a plastic composite that doesn’t conduct cold and is more flexible, which helps the unit handle solar pumping much better.
- Maintain Your Frames: Keep the weep holes (drainage channels) in your frames clear of debris. If water can’t drain away, it will sit against the seal and cause it to fail prematurely.
- Gentle Cleaning: Avoid power washing your windows or using harsh solvents. Mild soapy water is all you need to keep the glass and seals clean.
- Manage Humidity: Use extractor fans in kitchens and bathrooms to keep indoor humidity levels in check, reducing the stress on your window’s interior surfaces.
The Role of Warranties and Guarantees
If your windows are less than 10 years old, check your paperwork! Many reputable manufacturers offer 10- to 20-year warranties against seal failure. If you are within that window, you might be able to get the replacement glass for free (though you may still have to pay for labor).
When we handle glass replacement in Colorado Springs, we ensure that the new units meet or exceed original specifications, giving you a fresh start on your window’s lifespan.
Frequently Asked Questions about Blown Windows
Can blown double glazing be repaired without replacing the glass?
Technically, “defogging” exists, but we don’t recommend it. It doesn’t fix the broken seal or restore the insulating gas. The only way to truly “fix” a blown window and restore its energy efficiency is to replace the sealed glass unit entirely.
How much does it cost to fix a blown window in 2026?
In April 2026, the average cost to replace a blown glass unit ranges from $50 to $150 for small panes and $140 to $400 for standard-sized windows. Specialist glass (like tempered, Low-E, or extra-large units) will be on the higher end. This is significantly cheaper than the $200–$1,200+ you would spend on a full window replacement.
How long should my double glazing last before it blows?
High-quality double glazing should last between 15 and 25 years. However, in the harsh Colorado Springs climate, windows on the south-facing side of a house (which get the most sun) may fail closer to the 15-year mark due to increased solar pumping.
Conclusion
Blown double glazed windows are an inevitable part of homeownership, especially here in the Pikes Peak region. While the mist and fog are frustrating, they don’t have to mean a massive financial headache. By identifying the problem early and opting for a glass-only replacement, you can restore your home’s beauty and energy efficiency for a fraction of the cost of new windows.
At Complete Window Care, we specialize in exactly these kinds of smart, cost-effective repairs. We’ve helped thousands of neighbors in Colorado Springs save money by focusing on what actually needs fixing—the glass—rather than upselling you on frames you don’t need.
If you’re tired of looking through a foggy haze, don’t wait for winter to drive your heating bills up. The warning signs for window glass replacement are already there—let us help you clear things up.
Ready to see clearly again? Book a professional glass replacement consultation with our expert team today!