Thermal Insulation: Insulating Glass

Are you envisioning a big, picture window, yet know that double-glazed windows lose heat tenfold compared to walls? What if we said that with technological breakthroughs, there might be a way to design your dream home with the window game of your choosing without compromising on comfort?

The Ins and Outs of Insulating Glass

Theoretically, there are very few ways to insulate a window:

• Shutters (manual or mechanical)

• Storm windows (interior or exterior)

• Thermal curtains

• Plastic film 

Since none of the above methods are foolproof, researchers opted to develop a new type of glazing. Say goodbye to single-pane windows, and hello to laminated double- or triple-glazed windows.

For glazing to be labelled as insulating, it must be made of two or more panes, separated by an air space and sealed. Therefore, the gas found between the two panes ensures thermal insulation. 

The Benefits of Insulating Glass

There are four key values used to measure a glass unit's energy efficiency:

• U-value: measures heat transfer rate

• Solar heat gain coefficient (SHGC)

• Energy rating (ER): the balance between the U-value and SHGC 

• Centre-of-glass rating: only the glass unit’s energy efficiency (not the product as a whole)

The following values measure the glazing’s characteristics, and determine its advantages:

1. Reduced heat loss

2. Improved energy efficiency

3. Reduced energy bills

Reduced Heat Loss 

Typically, glass units have a U-value between 0.20 to 1.20. The lower the value, the better (efficiency-wise). To lower the value, the laminated glass panes are sealed together with an argon gas cavity sitting in between. 

Why argon? Because its thermal conductivity is 300 K, meaning 0.018 W/mK, compared to 0.026 W/mK for air. This means that if the ambient temperature is 27°C (80°F), argon is 31% more efficient than air.

While CO² is slightly more efficient, the latter is harder to produce than argon. In fact, CO² is only found in the air at heights of 400 ppm (parts per million), whereas argon represents close to 1% of the air we breathe. 

However, manufacturers are striving to add krypton instead of air or argon gas as, although its concentration in the air we breathe is only 1.1 ppm, its thermal conductivity coefficient reaches 0.009 W/mK. It’s well worth it.  

Improved Energy Efficiency

Insulated glass has a dual purpose:

• Insulate indoor spaces against the cold outdoors

• Preserve indoor warmth 

Due to its low thermal conductivity coefficient, the air or argon gas cavity between the glass panes preserves indoor spaces from outdoor conditions. Likewise, the glass unit’s low emissivity (low-e) allows for heat retention. We’ll circle back on the subject matter. 

Reduced Energy Bills

Let’s talk numbers. The most cutting-edge ENERGY STAR-certified window allows for annual savings of 7-15% on energy bills, meaning $500 a year. 

Technical Functioning of Insulating Glass

Insulated glass is made with two or more layers of glass panes separated by a cavity filled with either air or inert gas, thereby creating a thermal barrier. This concept prevents heat loss during winter and limits heat transfer during summer, improving a building’s energy efficiency.

The Different Layers and Their Respective Functions

A double-glazed window pane is made up of the following: 

• Two glass panes

• Gas

• Desiccant

• Seal

Double-glazed windows are made up of two glass panes, which are sealed together with the help of a spacer. The cavity created by the spacer holds argon or krypton to improve the sealed unit’s insulation. 

The spacer holds a desiccant to prevent fog from building up in between the glass panes. It's held together by a urethane sealant, which improves its air-tight feature. 

As such, multiplying the sealed units mechanically increases the window’s insulation capacity, hence triple-glazed windows, meaning three glass panes instead of two. 

The only downside to additional glass panes is limiting the amount of natural light filtering into a room. 

Mechanisms Limiting Heat Loss

As mentioned, argon gas is 31% more effective than air in terms of thermal conductivity. However, when considering a window as a whole, insulation is merely improved by 10% with an air-filled cavity compared to an inert gas cavity like argon or krypton. 

Thermal insulation isn’t solely determined by the glass panes, but also by the window’s frame, stripping, etc. To tip the scale in your favour, laminated glass manufacturers opted to develop different glass types, such as Low-E. 

The latter, which we’ll circle back to, is equipped with a low emissivity coat, hence its name, preventing heat transfer. 

The Purpose of a Spacer in Insulating Glass

The spacer’s the centrepiece, the one that makes all the difference compared to a single-pane window. The spacer allows for an air space (a cavity) between the two or three glass panes.

Gas—argon or krypton—will later be injected into this air space to reinforce the sealed units’ insulation. The spacer is either made of:

• Aluminum 

• Stainless steel 

• Hybrid (warm edge) 

The window’s weak point, commonly found near the pane’s edges, depends on the quality of the spacer. Today, high-performance spacers are typically made of aluminum and stainless steel (hybrid). 

Laminated Insulating Glass

Laminated insulating glass is made of at least two glass panes, each of which is 0.15 in (4 mm) thick, on average. This type of glazing system has sealed units reinforced with a polyvinyl butyral (PVB) interlayer.

This film has a dual function: 

• Safeguard against window breakage

• Deter break-ins

Its primary function is to protect dwellers. Therefore, in the event of a physical impact, the glass pane will shatter instead of breaking into sizeable pieces, capable of severing an artery.

Nonetheless, while ensuring everyone’s safety, laminated glass is also reinforced against potential burglaries. It’s harder to break through, therefore rendering access to interior knobs and handles challenging, even if violently hit or using a glass cutting disc. It’s an especially appealing option for picture windows, for example. 

Custom-Made Glazing

Most glass manufacturers offer custom-made glazing options. Therefore, if your windows exceed standard dimensions, you'll still find suitable insulating glass solutions. For more information, refer to the manufacturer’s standard-size catalogue. Some might have over 50 different types of windows, with up to a dozen different sizes per window type.   

What’s the difference between single-, double-, and triple-glazed windows?

Let’s break it down for you—single-, double-, and triple-glazed windows: the difference in terms of energy efficiency, soundproofing, and cost.

Energy Efficiency

We mentioned earlier in the article four values to consider when choosing a window. The truth of the matter is, there’s a fifth one, which is commonly used by window manufacturers and retailers: the R-value.

The R-value is the thermal resistance coefficient. It’s measured in square feet per hour and °F per Btu. Unlike the U-value, the higher the R, the better the glass. 

Therefore, the R-value of a double-glazed window is typically between 3 and 3.8. As for triple-glazed, the coefficient is usually between 7 and 8.

What does this mean in terms of heat retention? Double-glazed windows are 40% more effective than single panes, but also should you replace a window with an R-value of 3 with one with a value of 5, you’re reducing heat losses by 30-40%. 

By opting for triple-glazed windows, heat gain can soar up the 50%. In other words, with good glass panes, the heat in your home is directed inwards, not outwards.

Soundproofing

Acoustic comfort is glaringly obvious when switching from a single-pane window to a double-glazed one. It’s all the more evident when opting for triple-glazed models. 

However, it might be ineffective depending on where you live (near high-traffic roadways and airport air corridors). 

In such circumstances, manufacturers may suggest using double-glazed windows with a glass pane that's thicker than the other and a wider spacer in terms of air space. As such, you’ll have a pane that’s 0.15 in (4 mm) thick, while the other is 0.40 in (10 mm). 

Proof in point that standard triple-glazing isn’t always the better soundproofing option compared to double-glazed windows that are specially designed to act as a buffer against noise pollution.  

Cost-Wise

Naturally, single-pane windows are cheaper, but they also have the lowest energy efficiency. In fact, for a while now, double-glazed windows have been standard practice in Quebec. It’s still affordable and unparalleled, performance-wise. 

Essentially, in terms of triple-glazed windows, retail prices are the biggest hindrance since they’re 10-15% more expensive than double-glazed windows. Here are some tips to make the best and most informed decision when it comes to your house.

Two Tips to Make an Informed Decision

Tip 1: Target your windows

Given the sheer cost of triple-glazed windows, choose the quality of your glazing based on the following: 

• Size of the window

• Positioning (south-facing, etc.)

• Room in which it’ll be installed 

Should you decide to switch out all your windows for triple-glazing, it’ll cost you a pretty penny, thousands of dollars even. To avoid spending all that money, you can target the windows you think need triple-glazing, and those that don’t.

As such, a picture window may require triple-glazing due to its size. Keep in mind what we mentioned in our introduction: double glazing loses heat tenfold compared to a wall. 

The same thing can be said about north-facing windows in your house. However, you can differentiate your needs based on, for example, basement windows and ground-level windows in your home.  

Tip 2: Determine your needs 

Are you looking for:

• Soundproofing

• Thermal insulation

• Light 

Should you be looking for quality soundproofing, specially designed double-glazed windows are certainly the best option in terms of value for money compared to triple-glazing. However, in terms of thermal insulation, triple-glazing takes the lead.

As for daylight, single-pane windows are by far the best option. Hence, double-glazed windows would be a happy medium between the two.   

Other Options to Improve Door and Window Thermal Insulation

Glass Films

Commonly referred to as “shrink film,” it’s a plastic-based film that’s directly applied on the inside-facing surface of a window. The film is: 

• Flexible 

• See-through 

• Thin 

Such a film has one installation method. Its outer polyester layer reflects heat, sending it back inside the room, serving as a low-e coating.

Its inner polyurethane (or polyethylene) layer prevents a part of the heat from reaching the glass pane, and therefore from seeping through, controlling heat transfer. 

Vacuum Glazing

Vacuum glazing still has an air space—either filled with air, argon, or krypton. This cavity is found within the glass pane itself. It significantly limits heat loss by: 

• Convection 

• Conduction 

• Radiation 

The only hiccup: this type of glazing isn’t laminated and its overall quality is questionable due to the fragility of the welds. 

Therefore, vacuum glazing is efficient in terms of thermal insulation (0.4 to 0.7 W/m2.K) and soundproofing, yet it’s still rather expensive compared to standard glazing.

FAQ About Insulating Glass

What is the best insulation for windows?

The best thermal insulator is triple-glazing.

The best soundproofing is double-glazed windows with one pane thicker than the other and a wider spacer. 

Does double glazing insulate from heat?

To know for sure whether a type of glazing acts as a heat insulator, you have to consider its emissivity. Meaning, its capacity to radiate heat. Emissivity is assessed through a value between 0 and 1.

For example, single-pane windows have an emissivity coefficient of about 0.84. This means that 84% of the heat seeps right through it, to then only be restored on the other side. In other words, during winter, heat filters out the home, and in the summertime, it seeps in. 

Double-glazed windows insulate against heat, especially if it’s made with a low-e coating. 

What type of glazing is best to block out heat?

Low-e glass is the best option to block out the heat. Its low-emissivity coating safeguards your home against outside heat during summertime and prevents heat losses during winter. However, similarly to triple-glazed windows, you’re taking a back seat in terms of daylight filtering through with these thicker glass panes. 

Last but not least, insulating glass turns out to be the most effective solution to improve thermal insulation in a home. By investing in this innovative product, not only will you be saving significantly in terms of energy consumption, but you’ll also be creating a cozier and more eco-friendly environment. Opting for insulating glass means making sustainable choices in terms of energy efficiency and your daily well-being. 

Cutting-Edge Green Thermal Insulation

Insulating glass positions itself is the flagship solution in terms of thermal insulation, providing an eco-friendly and efficient solution. The benefits listed, such as improved energy efficiency and reduced heating costs, further highlight its key purpose in modern construction. It’s essentially an invitation to embrace innovative technologies to build increasingly sustainable, cost-effective, and eco-friendly spaces.