News & Events

Energy Saving Low E Windows

One of our goals at Spectrum Inspection Group is to educate real estate agents regarding some of the structural and mechanical idiosyncrasies that exist in Las Vegas Valley homes. The following information is meant to provide you with some of the fundamentals about Low-E windows.

Preface:  This information is intentionally rudimentary in nature and we do not get in-depth into the science of Low-E.  In this article we’re not going to discuss emissivity values, reflectivity, thermal reflective values, Pyrolytic CVD, Magnetron Sputtering and things that you do not need to know in order to do your job.  If you want that kind of technical information then we have provided links below to references where you can get all the technical information pertaining to Low-E that you could possibly want. 

With the information we are providing in this article you will be able to speak intelligently to your buyers and provide them with credible, accurate information about Low-E windows.  Interested?  Please read on!

Low-E Windows

First you need to know that energy saving Low E windows have been around for a long time now and they are a fabulous positive feature to have in a home.  They cut electric bills dramatically and are essentially maintenance free components.  Energy-Stars homes have them and for many years the prominent home builder Pulte was known to guaranty the energy costs associated with their homes and Low-E windows have played a key role in making this happen.

If you are a Listing Agent and you are listing a home that has Low-E windows installed you need to highlight the feature.  If you are a Buyer’s Agent and your Buyer’s are looking at two nearly identical homes; one with Low-E windows and the other without you should advise your buyers of the significant advantage the home with Low-E has over the home with standard windows.

What is meant by Low-E?

Low-E is an acronym for Low Emissivity.  “Emissivity” is an unusual word.  The root word for emissivity is “Emit”.  To put it simply: Low-E windows reduce the amount of heat or thermal energy that is emitted or passes through the glass.  To really simplify it you can say that one of the qualities of Low-E windows is that they reflect heat.

Low-E windows also reduce the amount of ultraviolet radiation that comes through a window and will reduce the amount of sun bleaching of furniture, flooring, window treatments and other interior components of the home.

How do they work?

First you need to understand that Low-E windows are almost always dual pane windows.  In dual pane windows there are two (2) panes of glass or “glazing” in the window.  A microscopic layer of metal oxide is layered on the surface of one of the panes of glass.  This layer of metal oxide reflects the thermal energy and reduces the amount of energy that is emitted on the opposite surface.

The location of the microscopic layer of metal on the glass is very important.  In Las Vegas where we live in a predominantly hot area of the country Low-E windows are used to reduce the amount of thermal energy (heat) entering the home.  Low-E windows are also used in cold northern climates of the country where the windows are “reversed” to prevent the amount of heat loss from the interior of the home to the exterior through the windows.

When I say that the location of the layer of metal oxide is very important you need to understand why.  Because many people aren’t aware of the importance of the location it has caused many problems for many homeowners.

A dual pane window has two (dual) panes of glazing and each pane of glazing has two sides. This gives us a total of four sides of the glazing.  The surface that is on the exterior of the home is known as surface #1.  The other side of that pane of glazing is known as surface #2.  The surface that you can touch by putting your hand on the window in the interior of the home is known as surface #4.  The opposite side of that piece of glass is known as surface #3.  Look at diagram #1 for clarification.

Between the two panes of glazing is a space.  Remember that the atmosphere between the two panes of glazing is not filled with air; it is filled with an inert gas like nitrogen or argon which greatly contribute to the window’s insulating abilities.

In hot regions of the country the Low-E coating is applied to surface #2.  This reflects the heat before it enters the space between the two panes of glazing.  In the cold region of the country the Low-E coating is applied to surface #3 to keep the thermal energy inside the home and prevent it from escaping.

I have a fair amount of critic’s out there so I need to provide the caveat regarding the location of the Low-E coating.  Low-E can never be applied to a pane of glazing that has another coating applied.  So, in some cases, where the outer pane of glazing is tinted on surface #1 then the Low-E coating is applied to surface #3.


How do you determine if a window is a Low-E window?  Contrary to what some builders’ superintendents might tell you it is impossible to see the Low-E metal oxide coating.  I have heard superintendents tell people that the green hue to the window demonstrates that it is Low-E.  That’s not true.  Some clear glazing windows will provide a greenish hue when you look at them from a certain angle. There are only two ways to determine if a window is a Low-E window;

  1. From the marking provided by the manufacturer of the window.
  2. Utilizing a Low-E meter.

Some manufactures of Low-E windows will stamp an arrow between the panes of glazing pointing to the pane that is coated with metal oxide.  Many window manufacturers put absolutely no permanent marking on the glazing assembly to indicate which surface has the Low-E coating installed.  If the window has no markings at all then the only way to determine that the window is Low-E is with a Low-E meter.

It is important that you understand that under the laws that govern home inspectors and the state of Nevada inspectors are not required to review a window to see if it is Low-E and verify that it is correctly oriented.  And of course, we review Low-E windows in the course of our inspections because we feel it’s too important not to do so.

It is very common to find “reversed” Low-E windows in Las Vegas homes.  By “reversed” we mean that the window is improperly oriented and installed in such a way that it keeps heat in rather than keeping heat out.

A True Story..

We once inspected a 4500 ft.² home in Southern Highlands for the buyer of Dennis Yates with Windermere Prestige Properties. This semi-custom home was four (4) years old and had ninety-four (94) windows installed.

During the course of the inspection, on the inside of the home, the inspector put his hand on one of the windows and it was so hot that it nearly burned his hand.  The window was exposed to direct sun and was radiating an enormous amount of heat.

Utilizing his Low-E meter the inspector reviewed every window in the home for proper Low-E orientation.  He determined that fifty-four (52) of the ninety-four (94) windows were installed inside out.  It was summertime and when you stood in front of one of these windows it felt like you were standing in front of a blast furnace.

As you can imagine no one at the inspection was pleased to hear that he determined that fifty-two (52) windows were installed inside-out.  The sellers were absolutely furious and the Listing agent just plain did not believe anything was wrong with the windows.

The Listing Agent contacted the builder and a lot of technical sheets were e-mailed back and forth for nearly a week.  (Luckily Buyer’s Agent Dennis Yates was a former licensed General Contractor.) Finally, a week later, our inspector met back at the property with the buyers and their agent, the listing agent and the seller, the builder, and a representative of the window contractor who had installed the windows four years ago.

The window contractor rep arrived at the scene with the very same and exact Low-E meter our inspectors use.  Within fifteen (15) minutes the window contractor rep had performed his own independent review and said, “Yup, they’re inside out.”

This happened on a Friday.  Everyone was pretty dismayed that this issue would push back closing.  But the following Monday, at eight o’clock in morning, the window contractor arrived back at the home with a four (4) man crew.  Before twelve (12) noon they had completed the job and had reversed all fifty-two (52) of improperly oriented Low-E windows.

Later it was determined that this home had historically high electrical energy bills from the very first summer.  The air conditioners were running almost continuously all summer long.  The homeowners, on several occasions, had an air conditioner contractor review the units and they were always found to be operating properly.  The A/C’s were running fine but they were running almost continuously because of all the heat emanating from the improperly oriented Low-E windows.

Do Home Inspectors Review for Low-E?

The State of Nevada does not require home inspectors to review the home for either the presence or orientation of Low-E windows.  Home inspectors are permitted to exceed the standards predicated by the State so if they wanted to review the home for Low-E they are permitted to do so.  However most inspectors still don’t review the windows for Low-E because of the significant  amount of extratime it adds to the inspection.

All Spectrum Inspection Group inspectors now carry the ETEKT+ AE-1600 series Double Pane Low E Coating Detector.  We now review all windows for the presence and proper orientation of the Low-E metal oxide coating and there is no charge for this additional service.

As is always the case whenever we discover an issue we also provide a path of resolution for addressing the issue.  Here are the most common:

  • In many case an improperly oriented window is the responsibility of the contractor who installed the window.  Contact the window contractor who installed the windows.  In some cases you may need to contact the builder to ascertain the contractor’s contact information.  Since this is clearly an installation / construction defect issue returning the windows to their proper orientation is often accomplished at no charge to the homeowner.
  • In instances where the age of the home relieves the contractor from responsibility understand that the cost to the homeowner to correct the issue is very low.
  • To correct this issue contact a licensed and qualified Window Contractor.  He will perform the follow steps:  The exterior retaining trim is removed from the window casing, the glazing unit is removed, reversed, and then reinserted, the retaining trim is reinstalled and the repair is complete.  The process takes mere minutes to accomplish.

Advanced / Technical Information

For those of you who are interested in the technical aspects of Low-E windows the following links should be reviewed:




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