If your double glazed windows have turned foggy, misty, or show condensation trapped between the two panes of glass, don't panic — and don't call a glazier just yet. You can fix this yourself at home with basic DIY skills and save hundreds of pounds in the process.
Why Do Double Glazed Windows Go Foggy?
Every double glazed unit has a hermetic seal around the edge that keeps the gap between the two panes of glass airtight. Over time — typically 15 to 20 years — this seal degrades due to a process called solar pumping. Once the seal fails, moist air enters the gap. When the temperature drops, the moisture condenses on the inner surfaces of the glass, causing that familiar foggy or misty appearance.
The traditional solution is to call a glazing company and have the entire sealed unit replaced. For a typical home with several affected windows, this can cost £1,000–£3,000+. But there is a far simpler and cheaper alternative.
The DIY Repair Method
The Condensation2Clear method works by drilling tiny holes through one pane of glass, allowing trapped moisture to evaporate naturally, and then fitting one-way valves that prevent new moisture from entering while allowing any future moisture to escape.
What You Need
- A Condensation2Clear repair kit (available from our shop)
- A standard power drill
- A spray bottle with water (for lubrication)
- About 15–20 minutes per window
Step 1: Identify the Outer Pane
You'll be drilling through the outer pane only (the pane facing outside). An easy way to identify this: place your finger on the glass — if the condensation is closest to your finger when you touch the outer pane, you've found the right side. If there's a gap, it's the inner pane.
Step 2: Drill the Holes
Using the glass drill bit provided in the kit, drill two small holes (3mm) through the outer pane. Position one hole near the top of the window and one near the bottom. Keep the drill bit wet with the spray bottle while drilling — this keeps it cool and prevents the glass from cracking.
Important: Use minimal pressure and let the drill bit do the work. Glass drill bits cut slowly but cleanly. Never force the drill.
Step 3: Let the Moisture Evaporate
Once the holes are drilled, warm air will circulate between the panes and the trapped moisture will evaporate naturally. Depending on how much condensation is present and the weather conditions, this can take anywhere from 24 hours to 14 days. You'll see the fog gradually clear from the edges inward.
Step 4: Fit the One-Way Valves
Once the window is completely clear, fit the one-way valves (included in the kit) into the drilled holes. These clever valves allow any future moisture ingress to evaporate out, while preventing new moist air from entering. This means your window stays clear permanently.
Does It Really Work?
Yes — we've sold over 8,000 kits and helped customers clear more than 64,000 windows worldwide. Here's a recent example from a customer in Everett, Washington who cleared a large picture window in just 2 days.
How Much Does It Cost?
Our kits start from under £30 and can repair up to 4, 8, or 12 windows depending on the kit size. Compare that to £100–£300+ per window for a professional sealed unit replacement, and the savings are enormous.
Frequently Asked Questions
Will drilling weaken the glass?
No. The holes are tiny (3mm) and only go through one pane. The structural integrity is unaffected.
Does this work on toughened glass?
Yes, but you need a diamond-tipped drill bit (included in our Toughened Glass Kit).
What if the condensation comes back?
The one-way valves prevent this. Any trace moisture that enters will evaporate out through the valves. Thousands of customers report their windows have stayed clear for years.
Read more about why condensation occurs and what glazing firms don't want you to know.