Author: Joe Brose

Manufacturers make modern windows as double- or triple-glazed panes with an inert insulating gas sandwiched in between. When energetic heat-transferring particles bump up against the glass, the insulation radiates them back into the environment instead of allowing them to pass through. This prevents warm air from escaping in the winter and penetrating in the summer. 

However, this type of window relies on an energy-efficient seal – a component that stops insulating gases from flooding out into the environment. Sometimes these seals can fail. And that can lead to air leakage and greater reliance on climate control systems.  

Why Do Window Seals Break Down? 

There are specific reasons why seals or caulk can break down, but it is worth noting here that all seals have limited lifespans. Wood and aluminium seals last around twenty years while vinyl-framed windows will function anywhere from five to fifteen years, depending on the quality of the spacer. 

Reason #1: High Atmospheric Moisture

Ideally, you should purchase windows suited to the climate in which you live. If you don’t, this can cause the seal to fail. 

For instance, wooden windows are unsuitable for cold, wet environments. Swelling and warping of the underlying material can create gaps in the seal, allowing insulating gases (such as krypton and argon) to escape. 

Reason #2: Solar Pumping

Another common cause of broken seals is a phenomenon called “solar pumping.” When sunlight enters glazed windows, it heats the insulating gases inside. As it expands, it pushes up against the seals and begins seeping out (even if they are in good condition). Then, on cold nights, the gas cools, reducing pressure in the window, causing it to suck in unwanted air over time. 

As this process continues, it progressively fatigues the seal material, causing it to weaken and harden. Eventually, so much of the original insulating gas leaves the interior of the window that it loses performance altogether. 

It’s worth noting that most modern windows come with a bead spacer that allows the glass to expand and contract without putting excessive strain on the seal. This component extends the life of windows exposed to highly variable light and heat conditions. 

Reason #3: Condensation

When there is a large difference in temperature between the inside and outside of your home, the risk of condensation rises. Water vapor in the atmosphere passing close to cold panes condenses into water droplets that form on the surface. 

Infrequently condensation buildup won’t adversely affect the seal. However, if moisture occurs more often, it can lead to mold. And this causes damage. As mold grows, it penetrates the seal material, fatiguing it over time. 

Reason #4: Manufacturing Or Installation Defects

Lastly, you can have a broken window seal because of manufacturing or installation defects. These could include: 

• Failing to properly clean the surface of the window before installing the seal
• Incorrectly applying the seal
• Puncturing the seal during installation
• Failing to allow the seal sufficient time to dry before installation

Window installation experts can confirm whether this is the source of your problem. 

How To Tell If A Window Seal Has Failed

The clearest sign of seal failure is condensation buildup on the interior surfaces of your window panes. When seals first fail, the visible signs will be subtle (i.e. a very small patch of condensation). But over time, you may start noticing more significant moisture buildup between window panels. And, eventually, the entire window can become fogged. 

How To Respond To A Failed Seal

When a window seal fails, you have several options for how to proceed. 

1. Do nothing: When you suspect a failed window seal, one option is to do nothing. If you believe the failure is in its early stages, you usually have a couple of years before it will start having a meaningful impact on your bills. The downside is the condensation buildup. You may find the window fogging unsightly. 
2. Replace the seal: Another option is to replace the seal and then re-gas the window. This process allows you to avoid replacing the entire window, but it isn’t usually economical. 

Replace the window: The final – and probably best – option is to replace the entire window. Here, you have two options. You can either use insert replacements that preserve all of the existing interior and exterior trim – the more affordable approach. Or you can just go the whole way and replace everything in full replacement.

Energy-efficient windows are becoming increasingly popular. Consumers are looking for options that allow them to cut their bills and reduce their impact on the environment. 

Not all window technologies, however, are the same. 

In this post, we explore the meaning behind terms such Low-E, argon gas, and krypton gas you inevitably come across while shopping for windows. 

What Are Low-E Windows? 

Low-E stands for “low emissivity.” It refers to a special type of treated glass designed to reduce the amount of infrared and ultraviolet light entering your home, without sacrificing on visible light. 

The sun emits a vast range of electromagnetic radiation. Some of it is the visible light you can detect with your eyes. But much of it is in the infrared and ultraviolet bands which you can’t see, but still heats your home.

For homeowners in some areas, infrared is a problem. As it penetrates regular glass windows, it heats up surfaces it interacts with, increasing cooling costs. UV is also problematic. The energy it imparts causes heating, plus it also damages occupants’ skin and interior finishes (such as painted surfaces). 

Low-E glass, therefore, is helpful. In the summer months, it prevents some of the light outside the visible range from entering. And, in the winter, its high infrared reflectivity helps to keep heat inside your home, lowering your energy bills. 

You can measure the quality of low-E glass via the following metrics: 

• U-Value: The U-value is a rating that reflects the degree of heat loss the window allows. The unit of measurement is W/m²K which stands for watts per meter squared Kelvin. Also known as “thermal transmittance,” it helps to capture the rate of heat transfer through a structure, divided by the difference in temperature across the structure. So, in this case, the heat difference would apply to the inner and outer layers of the window.  
• Solar Heat Gain Coefficient (SHGC): The SHGC measures the fraction of insolation (sunlight) the window allows to penetrate into your rooms (including light in the infrared and UV bands). The lower the SHGC, the better the glass can shade and reflect energy from the sun, reducing cooling costs in the summer. The higher the SHGC rating, the more effective the glass will be at collecting solar radiation, making it better for heating homes in the winter. 
• Visible Light Transmittance (VLT): VLT measures the fraction of visible light the glass permits to enter. Defined scientifically, visible light encapsulates all electromagnetic radiation with wavelengths between 390 and 780 nanometers. Typically, clear glass has a VLT of around 0.75 to 0.92, meaning that it allows 75 to 92 percent of regular light to enter the building. Colored glass can have VLTs ranging from 0.15 all the way up to 0.85, depending on the hue and tint. 

Good Low-E glass, therefore, should have a relatively high VTL, but low U-value and relatively low SHGC. 

What Are Argon Gas Windows? 

Glazed windows work by sandwiching gas between two panes of glass. Gases are good insulators, so when incorporated into windows, they help to keep the temperature of your home constant, regardless of the weather outside. 

Argon gas windows use argon to fill the gap between panes. It is a top-performing insulating gas because it has molecules that move six times more slowly than regular air, reducing heat transfer. It is also odorless and non-toxic which makes it safe and convenient for home use. 

What Is Krypton?

Krypton, like argon, is a noble gas, but with even higher performance. It is much heavier than argon, so its constituent molecules move twelve times slower than regular air, making it one of the best known insulators.

Kryton is also rarer than argon, so krypton windows typically cost around 40 percent more than argon windows. Some windows offer a mixture of krypton and argon gas to balance price with performance. 

You typically find argon gas in windows with a space of ½ an inch or more between inner and outer panes, while krypton windows typically have a ⅜ gap (usually found on triple-glazed models). 

While krypton windows are more expensive upfront, data from the Efficient Energy Collaborative suggests that they could offer savings over the long-term. Compared to an argon-filled window, each kryton version could save homeowners around $20 per year. Multiply that by ten exterior windows on the average home, and savings could reach $200 annually. 

Air leakages can be a problem in argon gas windows. Over time, argon gas can escape and get replaced by air. When this happens, condensation can build up on the interior surface of window panels, especially during spells of cold weather.