Themo shots of windows

I need some help understanding the science of scanning windows. I would say 90% of windows dont have a mfg’er name on them, let alone knowing if they were mfg’ed with argon gas between the panes. An ITC course by FLIR mentions a halo effect if the gas has leaked out. The double pane windows in the pic did not have any moisture between the glass and 3 have this halo effect and one does not? Outside temp was about 30F and inside about 65F.

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Negative pressure between the glass sucking the two glass panes together, Window failure,

Negative pressure between the glass sucking the two glass panes together, Window failure,

Scott can you expand on your answer? I am interested in knowing how you came to that conclusion. I too, am somewhat new to IR and am always looking to glean a nugget of information from those more knowledgeable than I am.

Fast forward to 25:00.


I was waiting for all the Infrared pros to chime in but nobody has, I have not looked at Martins video as of yet.

That mention training (ITC)has very little about windows, only one image. What is said that " as the seal fails the glass moves closer together and the energy is absorbed from the inside and outside". As far as pressure goes, if there was a sealed box and it got a hole in it how could the pressure be negative inside? Wouldnt it just go to ambient pressure? What causes the coolness in the middle of the windows? Why does it concentrate in that pattern? I have done additional research and took all the internachi training and i cant find the answers to these questions.

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Well, I am not an infrared pro but I have installed thousands of Andersen windows. I am aware of one of the Andersen windows defects, I have worked alongside an Andersen window Rep replacing defected windows, Andersen window has a 20-year warranty on their glass. This is not a complete explanation but something to expand on, so google Andersen glass failure due to negative pressure. Have a great day. :+1: :smiley:

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May I suggest taking a course on building science. That course may describe the bellow effect of window glass.

The cause of the pattern is described in the video.

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Scott…Thx for all the info. I did some googling and this link had some interesting info.

What i found out is that the gas can partially leak out and then the window somehow reseals. This causes the pressure difference. In some cases the center of the glass panes can actually touch. This narrowing dead air space must be responsible for the halo in the middle under IR. If you put a piece of masking tape on the outside and inside of the panes you can get a view of the thickness in relation to the aluminum side bars. I will put some tape in my tool bag and try this when i find some more failed window scans. The pic i attached was of Andersen Windows.

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There is a date code down in one of the corners, if the window is less than 20 years old Anderson will replace the sash.


Morning David.
Hope this post finds you well.

There can be several explanations for why the center of the thermal pane glazing appearing cooler and in a circular pattern. Reflectance.

If you wish to find ASTM and manufacturing standards it will be etched, stamped or embossed on the glazing or spacer bar, as will Argon or films used to treat the glazing for energy efficiency.

As for diagnosing thermal pane or any windows for that matter. Look/measure for air leaks, energy loss, around the site constructed window frame and not the actual manufactured window.

As for diagnosing the actual manufactured window.
I using a normal point and shoot camera with good lens. Take a close up shots of the seals. Look for ware.
Another shot the spacer bar up close.
Look for desiccant power.

As for the manufactured frames.
Take images of damaged or broker compounds.

As for structured frames.
Poorly installed manufactured windows do not line up in site manufactured framed. Single/double hung window sash locks do not align. Rail and head do not align. The list goes on…

Fogging between thermal panes is one indication of seal failure.

Hope that helps.
Read my following post below for thermal cameras and reflectance.

You don’t need a Thermal Imaging Camera to see this defect, Look down the sidewall at an angle, about 10 to 15 feet away, and you will be able to see the negative pressure sucking the glass panes together when the light is just right you can see it from your vehicle driving down the road.


That may be true Scott but a picture in the report is easier to understand.


Awesome video, thanks for sharing!

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Morning David. I suspect the Infrared Thermal device or Camera you are using has limited functionality. Indicate to the members, what thermal imaging equipment you are using. What you set the camera’s parameters, emissivity for example. How far away you were from the subject in feet. What was your subject. Which window?

There are 4 windows. Move around taking images at different angles and focus in on 1 object. In this case, 1 window. What is in focus for one object does not correlate to the focus of surrounding objects.

From Fluke. Understanding and fixing infrared thermography issues on reflective surfaces

Increasing thermography accuracy on reflective surfaces.
The content visible in a thermal image is almost entirely based on the amount of radiation emitted from or reflected by the surface.
Reflective surfaces are inefficient emitters.
The presence of reflections is obvious, but as we move our position the objects being reflected typically change.
Surface Emissivity vs Reflectivity
Opaque (non-transparent) surfaces produce a combination of emitted and reflected radiation. Because the reflected radiation isn’t related to the surface temperature, we must tell the imager to disregard that portion of what it sees.
There are two situations where this correction is not as accurate as we would like, such as when:

  1. The surface being measured has an emissivity of less than 0.6.
  2. The reflected temperature is extremely different than the surface temperature

This limitation applies to all thermal imaging systems. It means that you cannot accurately measure the temperature of most bare metals. But there is a workaround.

Increasing thermography accuracy on reflective surfaces
Applying a piece of electrical tape to either a cold window glass (left) or a warm sheet of steel (right) with variable oxidation allows a thermographer to consistently make accurate radiometric temperature measurements. Note both materials are quite reflective. In both cases the emissivity is set for the value of the tape (0.95) with an appropriate reflected background correction value.

Hope that helps.

Thanks for the info Robert. I have just begun my education into IR. I took that image about 6 feet from the window with a CAT S61 which I realize is a low end piece of IR equipment. Resolution of 160X120.
I guess my goal in all of this is can i accurately use this S61 on a home inspection to find failed windows. When I think about the reflectivity of glass, if the image is reflecting some other heat source why wouldnt that source be evenly distributed over the glass? What causes the concentrated halo effect in the middle of the window that many claim is failed glass?
I will take the pointers from this discussion and try to refine my technique in the field along with other clues presenting themselves on the windows when i get this indication.

The argon gas has escaped, and the R-value is less in the center of the glass. Because of the negative pressure, the two panes of glass are closer together in the center, eventually the window will start to fog up over time.

This is limited functionality.
More to it than160X120 Resolution.
RESNET. Because there are many imagers in the market today that are not well-suited to use in building diagnostics, establishing minimum specifications for equipment was deemed critical.
Thermal sensitivity is specified at 100mK or better, while spatial resolution is defined by the minimum array size (120×120 or better) and a suggested field of view (FOV) of approximately 20 degrees.
The thermographer must also be able to adjust the span and level within either their infrared imager or their software. While “fixed-focus” systems are technically allowed, the onus is placed on the thermographer to ensure the images are in adequate focus; if not, another system must be utilized.

Why even go there? For windows glazing’s?
Moisture, Energy loss, Leaking duct work, Structural anomalies,.
With your equipment you can process/diagnose wall, ceiling and floor assemblies fast and use other equipment, a moisture meter, to provide qualitative information afterwards.

A good mid level IR camera will set you back >< $5,000.00
Keep us posted.

My client, in building, had an issue with an Andersen casement window the wouldn’t close. I looked at the arms and got the date code and number off the corner of the glass, like Scott said but this window was 28 years old.

I sent the pats that I needed off to the Andersen replacement factory and 2 weeks later the new and old parts came back to me without any charge. My client was really happy!

There are many window with equivalent “U” factors but the service is what you get extra with Andersen windows.


Dear David:

Infrared Inspections of Insulated Windows was recently featured as a Tip of the Week at our content-based website,

When viewed with a thermal imager, IGU windows with failed seals will typically present a ‘bullseye’ signature where the center of the bullseye represents the relative temperature on the opposite side of the window. For cold weather conditions (cold outside/warm inside), the bullseye will appear cool when inspecting from indoors; it will appear warm when inspecting from outdoors.

If you have not already taken infrared training, I would invite you to check out infraspection Institute’s training course, Infrared Inspections for Home and Building Inspectors. Normally priced at $1095, this course is available to InterNACHI members for only $295.

Hope this helps.

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