Low-E Glass windows: Everything You Need to Know

Primarily, the purpose of windows was to bring the light into the house. They protected it from the wind and rain and provided a view to the outside. Nowadays, advanced technology allows the production of windows that help us to control the temperature of the house. That matters because it makes an influence on your budget, as well.

That is a situation where Low-E windows (low emittance windows) can make a difference. Basically, they are windows covered with non-toxic, thin, and colorless coatings that decrease the effects of destructive UV rays and reduce your energy costs. Plus, they improve the energy efficiency of your home.

Glass Emissivity of Low-E Windows

Emissivity is the ability of the material to effectively emits energy as thermal radiation. Like every other material, glass can absorb, reflect, and emit a certain amount of thermal energy. Its scale showing emissivity goes from 0 to 1.

The average emissivity of regular glass is 0.95, which is pretty high value. That means your window glass allows the heat to enter your home during summer. On the other hand, the heat from the window air conditioner exits through the window during the winter.

Luckily, contemporary technology improvements can help with the energy efficiency of your home, including fantastic Low-E windows, which are one of the best innovations ever.

Preventing Ultraviolet and Infrared Light

All lights, including infrared, ultraviolet, and visible ones, are segments of electromagnetic radiation descending from the Sun to Earth. The heat of the Sun you feel in summer comes from the infrared waves. They are invisible, but their impact on all living beings living on Earth is immeasurable.

Some devices, such as toasters, lamps, and industrial heaters, can emit this type of light, as well. Actually, anything with the temperature higher than -451 F (-268 C) emits IR radiation.

On the other hand, ultraviolet rays are dangerous, and they may cause sunburn and skin cancer. They are responsible for the persistent efforts of glass manufacturers to improve their products and come up with solutions to prevent UV rays from entering the houses.

Nowadays, you can find Low-E windows on the market that fulfill all the necessary requirements. They block the unnecessary heat to come in through the windows and let visible light to come in, at the same time.

Also, Low-E windows have the improved panes that don’t allow the infrared and ultraviolet rays to go through, as is the case with ordinary windows. Therefore, you can replace traditional window insulation kits used to improve energy efficiency with a more durable solution.

Insulating Properties

Double-pane windows were a primary type of insulated windows for decades. They had two window panes with the space between them filled with an insulating gas, mostly argon.

Their purpose was to reduce the heat loss from the inside of the house in winter. Also, they gained heat from the outside of the house in summer. Thanks to excellent insulating properties, these windows were the primary choice for many citizens of the US until recently.

Later on, triple pane windows showed up on the market with increased insulation features. They were expensive, which influenced their usage in modern homes. Also, not every house construction was convenient for this type of window.

For these reasons, manufacturers install almost all the energy efficiency upgrades, including Low-E coating, on the double-pane windows.

Energy Efficiency of Low-E Windows

Several features of your windows determine their energy efficiency, including:

• R-value – It will tell you about the ability of your window to reduce the transfer of heat. When it is about windows, the high R-value is a desirable option.
• U-value (U-factor) – It measures the transfer of heat and its losing or gaining through the window glass. You can get this value by calculating the conduction of materials necessary in windows production. Keep in mind that the lower this value, the better the window.
• VLT (visible light transfer) – It determines the amount of light going through the window.
• SHGC (solar heat gain coefficient) – It shows the quantity of solar radiation that can go through the window. If we refer that this value can be between 0 and 1, an SHGC rating of 0.45 means that your window lets 45% of the solar heat through.
• Light to solar gain – It is the value showing you the ratio between the amount of light and radiation that can go through the window.

What is Glass Coating?

Glass coating is a process of applying a thin layer of metal, such as copper, tin, zinc, silver, or brass on one side of the window glass. That layer is thin and not visible, but it still has reflective properties.

In the beginning, the coating layer contained two layers, one made of metal oxide and the silver layer, as well. Nowadays, you can find an improved version with three layers, the silver one and two coats of metal oxide. Although this coating allows the light in, some windows may have a slight gray or brown color.

The manufacturers always place the coating on the inside of the window glass. Putting it on the outer side is impractical since there is a possibility to damage the layers while cleaning either with a window cleaning robot or manually.

Modern Low-E windows have a microscopically thin, transparent coating. Since it reflects heat, this layer will keep the temperature in the house consistent. There are two types of low-E coatings, including:

Passive Low-E coating (hard coat)

It is the coating that stops the condensation of the surface of the window glass while it is still hot. The process of making it is a pyrolytic way of making the glass. That way, the connection between the coating and the glass becomes very strong.

The window obtained in this way is an excellent choice if you live in a cold area. It allows solar heat to enter the home through the windows and reflects it from the inside. Unfortunately, with this type of window, you won’t get top-notch R-value and U values.

Solar control Low-E coating (soft coat)

This technique has developed recently. The glass is made in the vacuum chamber at room temperature. During the process, the manufacturers apply the coating by sputtering. After that, the glass is ready for a cut.

Since the connection between the window glass and the coating is not that strong, it can peel off over time. Usually, this type of coat requires additional reinforcement, such as a seal or laminate.

You should pick out this type of window glass if you live in a warm area. The U-value of this glass is better, which means that it provides better UV protection.

Determine If You Have Low-E Windows

In case you bought a house and you are not sure if you have Low-E windows, there is a way to test them. Firstly, you should know that most of the windows with Low-E coating are double pane windows.

That means there are four glass surfaces. Two of them are on the outer window pane, and another two are on the inner pane.

To check it, you should light a match or a lighter and put the flame close to your window glass. You will see that the flame reflects in the glass and creates four copies of it.

If all four flame reflections are the same, there is no coating on the glass. However, if you see three same flames, while the fourth is slightly different and a bit darker, the surface of the window glass has a coating.

What determines on which surface of the window the coating is applied is the climate. In the cold regions, the Low-E coating is often on the outer surface of the inner window pane. In the warmer ones, it is better to place these layers on the inner surface of the exterior window pane.

Low-E Windows and Plants

Since the Low-E windows are highly efficient in blocking the heat and UV rays, most people are not sure if it is safe for the plants to be in front of them. Keep in mind that these windows don’t block the light. So, they are an ideal solution for plants that require medium light.

Also, you can always check the VLT value of your Low-E windows. If this number is low, it means that less light goes through the window glass, and you should move some of your plants to a more convenient place.

Final Thoughts

If you look for new windows, you should find all the relevant information about Low-E windows. This type of windows will help you save some money on the heating bills in the long run. Except for energy efficiency and UV protection, they also prevent condensation and consequently reduce the occurrence of mold.

Nowadays, Low-E windows are the standard for energy efficiency in every contemporary home. They reduce harmful UV light without blocking natural light from entering your home.

If you want to improve your home, you should consider replacing your old windows with these extraordinary models, if possible. It will be an excellent and very cost-effective decision.

Low-E vs. Tempered Glass Windows

The world of windows has come a long way from what it once was. No longer do we simply choose a single-pane wood window and call it a day. Now we have double- and triple-paned windows, high-efficiency windows, and a wide variety of frame materials to choose from.

This post will tackle a few of our most commonly asked questions: what are low-e windows? What is a tempered glass window? Is one better than the other? Are they different at all? Follow along and you’ll find out all you need to know.

What Is a Tempered Glass Window?

The tempering process consists of cutting an annealed pane of glass to size and then exposing the pane to extreme levels of heat, after which it is rapidly cooled within seconds. By rapidly cooling the glass, the surface of the glass will harden much faster than the internal portion in order to create equal tensile stress.

The resulting pane of glass is many times stronger than standard glass types, making it highly valuable when installed in areas where window damage may be possible. Additionally, tempered glass is considered a form of safety glass because it “crumbles” into small pieces when it breaks rather than forming dangerous shards.

What Is Low-E Glass?

Low-emissivity, or “low-e,” windows actually refer less to the glass itself and more to a coating that is applied to the pane. Low-e coatings typically consist of metallic particles or oxides that are applied to a finished pane of glass before installing the window. These coatings offer a reflective barrier against ultraviolet and infrared light, both of which can pass right through a normal, untreated window. Equally important is that a coated low-e window will filter out these light types without reducing the amount of, or altering the look of, natural light that comes into your home.

Ultraviolet light contributes heavily to heat gain, an issue that a low-e window can remedy. By filtering out (or, more accurately, bouncing away) UV light, a treated window can drastically reduce the amount of heat that enters your home through the windows. A low-e treated window will keep your home cooler and more comfortable while also helping to minimize cooling costs.

Which Windows Should I Choose for My Window Replacement Project in Maryland?

In order to answer this question, first ask yourself another one: what are your goals? Do you want strong, durable windows that are guaranteed safe if they break? Or is efficiency, comfort, and home preservation more to your liking? Answering these questions can make the replacement process much simpler overall.

Or, if you’re interested, you can actually have both! Windows treated with a low-e coating can also be strengthened and tempered. And additionally, plenty of tempered window options include efficiency advantages like advanced sealing techniques. Many manufacturers offer these window options, and the investment could be well worth it if you want a durable product.

Choose Weather Shield Windows for Peak Quality in MD, VA, and DC

Interested in low-e or tempered window products that can be customized according to your wants and needs? Connect with Quality Window and Door to find out more about Weather Shield products! Weather Shield tempers their own glass in-house and offers a wide range of efficiency coatings, multi-pane options, and custom window products!

Looking for a quote on your new windows? Contact us now!

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All of our consultants have 10+ years of experience

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Glass windows and lower

All windows and doors offered at 1stwindows feature dual paned (also known as dual glazed) glass. If you require a custom glass configuration and do not see it listed please contact us at (562) 494-9069.

Glazing refers to the glass in a window or door and the act or process of fitting a window with glass. There are many different glass types and treatments available. Assembled below are descriptions of the most common glass types.

Low-E Glass
Low-E glass products give you year-round energy savings and comfort by helping manage the sun’s energy and the heating system energy in your home. Low-E glass products are coated with microscopically-thin, optically transparent layers of silver sandwiched between layers of antireflective metal oxide coatings. In the summer, Low-E glass products let in visible sunlight while blocking infrared and ultraviolet solar energy that drives up cooling costs and damages curtains, window treatments, carpeting and furnishings. And in the winter, Low-E glass products offer greater comfort and reduced heating costs by reflecting room-side heat back into the room. Emissivity is a measure of how much heat is emitted from an object by radiation. Heat is transferred to and from objects through three processes: conduction, convection, and radiation. For instance, on a hot night, heat will be conducted through a window from the outside, causing the inside pane to become warm.

Convection, or natural circulation, of the air in the room past the window will transfer some of that heat into the room. But the window will also radiateheat as infrared waves, which will warm objects throughout the room. This radiative heating is why you can feel the heat of a red-hot piece of metal (for instance, a heating element on an electric stove) from several feet away. Low-emissivity, or low-e, coatings are put on window panes to reduce the amount of heat they give off through radiation. In hot climates, where the outside of the window will typically be hotter than the inside, low-e coatings work best on the interior of the outside window pane. In cold climates, where the inside of the window is typically hotter than the outside, the low-e coatings work best on the inside window pane, on the side that faces toward the outside.

Laminated Glass
Laminated glass is produced by permanently bonding two pieces of glass together with a tough plastic interlayer (polyvinyl butyral) under heat and pressure. Once bonded together, the sandwich behaves as a single piece. The interlayer is invisible when viewed through the glass and with glass on either side, the finished lite is indistinguishable from plain glass when installed. Most often, laminated glass is produced from annealed glass, but heat strengthened or tempered can be used when special performance needs are present. The benefit of laminated glass is that if broken, glass fragments adhere to the plastic interlayer rather than falling free and potentially causing injury. Laminated annealed glass can be cut or drilled. Laminated glass is required in sloped glazing applications that exceed any of the following conditions:
The area of each pane (single glass) or unit (insulating glass) exceeds 16 square feet.
The highest point of the glass is greater than 12 feet above any walking surface or other accessible area. The nominal thickness of each pane exceeds 3/16 inch.

Laminated glass is highly effective in reducing noise thus improving Sound Transmission Ratings. The best design incorporates laminated glass in an insulated unit. The damping characteristics of the plastic interlayer combines with the attenuating characteristics of the air space of the IG unit to maximize sound reduction. Example: Two lites of 1/4″ laminated glass in an IG unit with a 1/2″ air space provide an STC rating of 42. This compares with two pieces of monolithic 1/4″ glass in an IG unit with a 1/2″ airspace the STC rating would be 35. Laminated glass eliminates 99.9% of ultraviolet rays, making it highly effective in protecting furnishings, displays, merchandise, etc. Standard laminated glass is 7/32″ with a .030 (approx. 1/32″) polyvinyl butyral layer.

Tempered Glass
The tempering process produces highly desirable conditions of induced stress which result in additional strength, resistance to thermal stress and impact resistance. Fully tempered glass must have a surface compression of 10,000 PSI (Annealed is below 3500 PSI) and heat strengthened must have a surface compression between 3,500 and 7,500 PSI. The basic principle employed in the heat treating process is to create an initial condition of surface and edge compression. The condition is achieved by first heating the glass, then cooling the surfaces rapidly. This leaves the center glass thickness relatively hot compared to the surfaces. As the center thickness then cools, it forces the surfaces and edges into compression.

Wind pressure, foreign object impact and thermal stresses or other applied loads must first overcome this compression before there is a possibility of breakage. In the heat treatment process the key procedure is application of a rapid air quench immediately upon withdrawal of hot (1200 degrees F) glass from the tempering furnace. The immediate and sustained application of an air quench produces the temper. A quenched condition becomes stable when the glass is reduced to a temperature of approximately 400-600 degrees F. Tempered glass is about 4 times stronger than annealed.

Solar Bronze
A brown ‘smoked’ tint. Designed to reduce solar heat gain.

Solar Gray
A gray ‘smoked’ glass designed to reduce solar heat gain.

Graylite
Unique among all tinted glass, offering a dark-gray, almost black appearance which provides excellent glare control, shading coefficient and ultraviolet screening.

Solex
A green float glass that has excellent light transmittance and reduces solar heat gain.

Evergreen
A green tinted, spectrally select glass that provides a high daylight transmittance and UV transmittance.

Azurlite
This spectrally select glass has an ‘aquamarine’ appearance and is excellent for high daylight transmittance and has a low shading coefficient.

Reflective Glass
The reflective coating is applied just like hardcoat Low-E through spraying (Pyrolitic process) during the float glass manufacturing process. It reflects light and heat with a metal oxide coating giving a mirror effect and minimizes solar heat gain, and ultraviolet light damage to interior as well as providing daytime privacy. May be tempered.

Heat absorbing and heat reflective glass can only be used on the exterior lite of a unit in order to avoid a build-up of heat inside the airspace, which will cause thermal stress cracks or seal failure. Reflective type glass works with the play of light. Example: During daylight hours you can’t see inside a building with reflective glass, (only your refection). At night there is just the opposite effect. You can see in, but the people inside can not see out.

Types of Reflective Tints

Solar Cool Gray
Solar Cool Bronze
Light and heat reflective. Has a low daylight transmittance, shading coefficient and relative heat gain.

Bronze Eclipse
Gray Eclipse
Blue-Green Eclipse
These are light and heat reflective. They have a low daylight transmittance, shading coefficient and relative heat gain.

Heat Mirror
Heat Mirror film is a window insulation material that is transparent to light, but highly reflective to heat. It consists of a specially coated film which is mounted inside an insulating glass unit, midway between the panes of glass. The result is a finished product which looks clear, but has a dramatically improved insulation performance. Compared with ordinary types of glass, Heat Mirror dramatically reduces heat loss and heat gain caused by conduction and radiation. These are two of the primary methods by which heat transfer occurs in glass. The third is convection.

Ordinary double pane and triple pane glass only reduce conductive heat flow, and have little effect on the radiated component of heat flow.

Heat Mirror combines a low-E coating with two air spaces to block both radiated and conductive heat flow. This unique construction enables Heat Mirror insulating units to offer higher insulating performance than other high performance glazing options. The transparent Heat Mirror coating is actually 90% as reflective as aluminum foil. It is optically clear and reflects heat back to its source.

Because there are many climatic regions in our sales area, there is a family of Heat Mirror products to provide optimum thermal performance for virtually any application in a wide range of climates. Similarly, within a climatic region, each specific application has different performance requirements on each elevation. The higher the Heat Mirror number (i.e., Heat Mirror 88 and SC75) the higher the solar transmission. Heat Mirror products with the highest numbers provide higher levels of visible light transmission and solar heat gain. The lower numbered products (HM 66, 55, 44) provide the best control of solar heat gain for the optimum control performance in southern climates on homes with significant solar exposure, or glass-intensive structures such as sky-walls.

Heat Mirror 88 is designed for northern climates, where warmth from the sun is desirable for supplemental heating. Heat Mirror 77 and 66 are designed for climates where overheating is the primary concern or on elevations like the south and west sides of a house where overheating can occur, even in the north. Heat Mirror 55 and 44 provide even greater levels of solar control for skylight, sunrooms and commercial buildings.

Heat Mirror Benefits
Superior insulation performance — has twice the insulation performance of standard insulating units.
Ultraviolet fading protection — Blocks out 99.5% of ultraviolet rays.
Provides improved sound control — Reduces outside noise 12% more effectively than standard insulating units.
Design freedom — Can increase the glazing area in the design of a home or commercial building because of its high performance characteristics.
Excellent shading coefficient
Excellent U-values

Obscure Glass
Some obscure or pattern glass gets its pattern by going through rollers after the float glass process that have the pattern on the rollers. It adds privacy where window covering are impractical or undesirable (bathrooms, sidelights) and is available in various colors and texture patterns provide a translucent of semi-opaque effect. It may or not not be tempered.

Types of Obscure Glass

Obscure
Our standard Obscure pattern

Gluechip
A fine etched pattern glass that is made by pouring an epoxy on the glass and letting it dry in a high humidity environment. The glue is then chipped away which removes portions of the glass.

Reed
A type of obscure with a vertical reed pattern.

Rain
A type of obscure with a rain pattern.