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Do your thermal windows sometimes fog up between the panes, or are there other signs moisture has made its way inside? Sorry to be the bearer of bad news, but those are tell-tale signs that a window seal has failed. Nothing lasts forever, and window seals can fail for any number of reasons — including old age. But there’s a lot you can do to reduce costs and get more life out of your windows. 

In this guide, I’ll explain how to help prevent seal failure, what to do if a window seal has failed, and how you can save money.

What Causes Seal Failure?

In order to know how to prevent seal failure, it’s helpful to understand a little bit about how thermal windows are designed, and why failures happen. 

How Thermal Windows Work

ESG_Blog5_Inblog-v1_1080x1080If you’ve invested in thermal windows, that was probably a wise decision if you live in an area known for having particularly hot or cold weather (or both, for those of us in the Midwest). These windows, also called Insulated Glass Units (IGUs) are designed to help your home be energy efficient. 

The way they work is by trapping air — or denser nontoxic gasses like argon or krypton — between two or three sealed panes of glass. Faulty seals or cracked panes make these windows less effective and can allow moisture to creep in and any dense gasses to leak out. 

6 Common Reasons Window Seals Fail

1. Extreme Weather

Frequent heavy rains can be tough on window seals. Water can cause corrosion in some weatherstripping products; eventually, that water can also make its way underneath seals, causing them to deteriorate. Extremely high or low temperatures and strong winds can also limit their usefulness, especially if the seals are already old or highly damaged. 

2. Mold

If your window seals contain rubber, mold can cause a lot of damage fairly quickly. That’s because rubber is porous, and there are plenty of tiny spaces where mold can hide out. If you see signs of mold around your window seals, you can kill the spores by applying a vinegar or alcohol-based solution. 

3. Old Age

Double or triple-pane insulated window glass typically lasts between 10 – 20 years, although that will depend on the manufacturer, the environment, and how well it’s been maintained. Updating the weatherstripping around a window can add to its useful lifespan. 

4. Poor Installation

Personally, I think it’s great whenever homeowners can save a bit of money with a DIY solution. But installing a thermal window requires precision, specialized tools, and the proper materials. If it’s not in your wheelhouse, leave it to the pros! Incorrect installation may result in window seals that don’t perform as effectively or fail faster.

5. Lack of Maintenance

Depending on the type of thermal window you purchased and its manufacturer, its maintenance needs may vary. It’s easy to forget about your windows once they’re installed, but keeping up with their maintenance goes a long way. If you do notice any gaps in your window seals, you should re-seal them with some caulk as soon as you’re able. 

6. Harsh Treatment

There are a few no-nos when it comes to thermal windows. Remember when I said heavy rain could be tough on them? Pressure washers are worse. They may be great for cleaning pavement, but don’t use them to clean your thermal windows. 

And that added note about extreme temperatures? That goes for heat guns too. Don’t use them to remove paint around window frames. 

What Happens When Window Seals Fail? 


Fogging, haziness, and distortion are what you’ll probably notice first when a window seal has failed. Your window will also lose some — but not all — of its ability to insulate your home. But that doesn’t mean you need to rush out and immediately buy a new window.

In fact, you might not have to buy a new window at all…

Pro Tips to Save Money 

First of all, these windows came with a warranty. Hopefully, when you bought your thermal window, you chose a high-quality product that was backed by its manufacturer for a decent amount of time. If your windows are still under warranty, get in touch with your contractor. 

Depending on how comprehensive your warranty is, replacement may be 100% covered.  

If your window is no longer under warranty, you can still avoid a big expense by contacting a custom glass expert to replace it. It’s far less expensive than buying a whole new window. 

Quick and Easy Window Replacement


Are you in the St. Cloud, MN area? Then you might have heard of us or seen our shop at 305 Franklin Ave NE. At East Side Glass, we’ve been faithfully serving the residents of St. Cloud since 1953. 

If you can bring your window sash to us, same-day service appointments are often available — just call ahead to make sure we can accommodate you. We’re also happy to come to you and replace your glass on-site.

Have additional questions about repairing or replacing your thermal windows? It’s one of our favorite topics! Click the button below to chat with an expert.

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