“Low E” refers to glass that has a film or coating that reduces radiant thermal energy. The idea is that it helps with the overall heating, lighting, and cooling costs of a building, property, facility, or home.
What does the E Stand for?
It means “low-emissivity” now what does that mean. Low Emissivity is the practice to limit the amount of light passing through a piece of glass. It is typically an application or coating that shades or tints the glass to achieve the reflective attributes that help to block the ultraviolet rays aka the sun.
How does it work?
Low E glass works this way; it reflects the infrared rays of the sun; this keeps the interior cooler from its warming in the summer. In the winter it works to keep the heat inside. It performs dual insulating measures.
Why is it utilized?
Low E glass has multiple applications. Low E glass is in homes, buildings, properties as well as cars, trucks.
Homeowners look for the glass to help the home perform better in the process of heating and cooling.
According to a Penn State University study, Windows typically occupy about 15 to 20 percent of the surface area of the walls. Windows not only add aesthetic looks and often an essential aspect of a home, but also a very significant component of home heating and cooling costs. Windows lose more heat per square foot of area in winter and gain more heat in summer than any other surface in the home.
Bigger the building bigger the savings.
Commercial, Multi-family, Hospitals, and Hotels are just some of the more significant buildings that use a lot of energy to heat and cool them. For this reason, architects and engineers look for this as a cost-saving measure. Also, “Green Buildings” is a designation that some owners seek to achieve, and the Low E glass can be one way to help make that status.
This article from usgbc.org defines what the definition of a Green Building.
The definition of green building
Green building is a holistic concept that starts with the understanding that the built environment can have profound effects, both positive and negative, on the natural environment, as well as the people who inhabit buildings every day. Green building is an effort to amplify the positive and mitigate the negative of these effects throughout the entire life cycle of a building.
There are many different definitions of green buildings. The best explanation would be the planning, design, construction, and operations of buildings with several central, foremost considerations: energy use, water use, indoor environmental quality, material section and the building’s effects on its site.
The https://new.usgbc.org/ goes further into Green Building and LEED buildings as well.
How much can it help?
The Department of Energy reports that you can save in the range of
12%–33% annually when utilizing a Low E storm window. Check out the report here.
When you are in the process of getting new windows for your building, you should explore the options your window installer can provide. Also, what kind of savings you could gain over time with a more efficient window. Many window manufacturers actually can submit a calculator to speculate how much you can save over time with more energy-efficient windows. I don’t know how accurate these speculations are, never tested or validated them or have research to back them up. I would consider these as guides but not to expect exact savings.
Now with commercial installations, window manufacturers provide more data to make sure that the owner will have an ROI for switching to their windows.
What does it look like?
Low E Glass, typically is not visible; in some cases, it can have a slightly darker tint to the overall piece of glass. There are reports that Low E glass can develop haze on the glass over time.
Can Low E be wrong?
There have been situations where consumers are claiming that the Low E glass installed has made issues for them in backyards/ courtyards. Due to its reflective nature, it reflects the heat into these areas affecting the exterior patios and common areas. In some cases, there have been people trying to link fires to the Low E glass. At this time there are no scientific studies to support this, but Low E does have it, detractors.
Low E Glass scams
During our research, we found reports on the internet (which as we all know means it’s true). Some consumers were duped with purchasing a higher-priced Low E Glass and instead got non-Low E Glass. A non-scientific test to identify Low E Glass is to hold a flame to it and if the last reflection is a different color. See below this youtube video of the test.
Typical options for Low E Glass
Hard Coat – A hard coat (Pyrolytic) Low E glass film is applied during the development of the glass. When the glass is in a molten state, the coating is added.
Soft Coat – A Soft Coated (Magnestron Sputter Vacuum Deposition– MSVD) Low E Glass is performed after the glass has been produced. The coating is applied to the interior part of the glass and can be more efficient than the hard-coated option.
Who makes it?
According to the energy star website, they provide information on the following manufacturers of energy-efficient or Low E windows:
Fixed or Picture Windows- List presented alphabetically
- A window Inc
- Anderson Corporation
- Capitol Glass/ Northern Windows
- Champion Window
- EnergyWall Window & Doors
- Ideal Window Manufacturing Inc.
- Interstate Window & Door
- Jeld-Wen, Inc
- Joyce Manufacturing Co.
- Kensington HPP, iNC
- Kohltech International, Ltd
- Kolbe Windows and Doors
- Marvin Windows and Doors
- Mathews Brothers Company
- Mercury-Excelum, Inc
- MI Windows and Doors
- NT Window, Inc
- OKNA Windows and Doors
- Pella Corporation
- Ply Gem Windows
- Polaris Technologies
- Provia Door, Inc
- Seaway Mfg. Corp
- Seven D Industries LP
- Simonton Windows, Inc
- Soft-Lite LLC
- Sunrise Windows, LTD
- Thermal Windows and Doors
- Thermo-Tech Windows and Doors
- Value Windows and Door Inc.
- Vector Windows
- Vinyl Window Designs Ltd.
- Vinylmax LLC
- Vista Window Company LLC
- Vytex Corporation
- Winchester Industries
- Wincore Window Company
- Window Mart Mfg. LLC
KPI’s or performance measurements for Low E
VLT Visible Light Transmittance – How much light is allowed to the interior space
SHGC – The rate/ amount of solar radiation allowed to pass through
Light to Solar – The difference between how much light can come through the glass and its coefficient rating
U Value – Rating factor of the quantity of heat escaped from the glass
Solar Heat Gain Coefficient (SHGC): This is the fraction of incident solar radiation that transmits through the window. It can be either directly transmitted and absorbed or radiated inward.
U-Value: This is the rating for a window based on how much heat loss it allows.
Visible Light Transmittance (VLT): The measure of how much visible light passes through the glass.
Light to Solar Gain: The ratio between the window’s visible light transmittance and its Solar Gain Coefficient rating.
Other things to consider with glass
Other than the Low E factor, of reducing heating and cooling cost of your building, there are a few other things to consider, especially when thinking of a capital project.
How does the glass rate for:
- Warranty – How long will the performance of the window last before we see issues with cracking or wear and tear
- What will be the effectiveness of the Low E over time
- How the glass perform for noise reductions
- What is the rating for R-Value
- What is the wind load?
- What is the process of replacement of glass due to breakage or cracks
- Is there a warranty if condensation happens
- What is the recommended cleaning process
- Is the glass suited to my region/ climate?
- With the warranty, what will the manufacturer cover? Is it just material or is labor included
- Is there a chance this glass will stop production in the future?
Hopefully this provides a comprehensive review of Low E Glass and factors to consider if you are thinking of installing it at your building, property or facility.