What You Need to Know About Thermal Imaging Cameras

I purchased my first thermal imaging camera back in 2009, it was an Extech i3 (made by Flir).  The $1200 camera had a resolution of 60×60, total pixels of 3,600 and shot photos only in thermal (no digital photo overlay).  If you don’t understand any of those terms, that’s okay, you will have a basic understanding of how thermal imaging works by the end of this article.  Oh, and by the way, you can now purchase more than twice the camera I had in 2009 with half the cost.

Let’s start with a misconception, a thermal imaging camera cannot see through walls as often seen in television shows and movies.  Thermal imaging “sees” temperature differentials in the camera’s field of view.  In the construction industry, this might be a thermal bridge, a heat pathway between the hot and cold side of a wall or roof.  You might see water leaks, wet or even slightly damp areas.  You can even see air leaks under the right conditions.  They are a handy tool that most contractors should have in their toolbox.

There are several manufacturers selling thermal imaging cameras that work well for the construction trades.  Flir (now called Teledyne Flir) is probably the best known, but there are other manufacturers.  I own a Hikmicro Pocket 2 I use all the time.  Seek and Fluke also produce cameras.  The manufacturers also offer reporting software where you can manipulate images and create reports.

Thermal imaging cameras come in a few different styles.  There are models that attach to a cell phone, one that look like the older style digital cameras, and others that have a pistol grip configuration.  Most take a thermal image and overlay a digital photo for more clarity in the picture.  Some will even shoot videos.

Let’s start with the smallest, and often least costly of the different camera options, the thermal image attachment for cell phones.  This class of camera is best for the DIY homeowner or the occasional quality control inspections.  These tiny devices simply plug into your charge/data port on the phone.  You need to be sure to get the specific camera that fits your phone’s port.  Around $200 will get you into a base model with limited features and low picture clarity.  Doubling the price of these plug and play thermal imagers produces better features and photo resolution, but the $400-$500 price range is where the next class of camera starts.  One drawback is that these cameras are so small, they are easy to lose.

The $500-$1000 price range (and even sometimes less) gets you into a dedicated thermal imaging camera.  There are both the pistol grip style and the traditional digital camera styles available at this price point.  The biggest improvement over the cell phone camera is photo quality and more standard features.

Prices above $1000 are camaras for people who use thermography regularly.  Energy auditors, building and quality control inspectors, and maintenance personnel all require more from thermal imaging.  Image quality and temperature measurements increase in clarity and accuracy at these price points.

Thermal Imaging Features and Terminology

The best way to maximize an investment in a thermal imaging camera is to take a class, either online or in person.  Formal training can greatly reduce the learning curve of the tool.  That being said, it is possible to learn on your own and become effective at interpretating the information the camera is providing.  There is some terminology and information that is helpful to understand.

For thermal imaging to work correctly, you will need a temperature differential between surfaces or between inside and outside a structure.  A difference of 10°F is enough, but the bigger the difference, the easier it is to “see”.  Some of my best thermal images have a difference of 50°F or more.

Information about a thermal image is usually included with the thermal image photo and may slightly differ by manufacturer.  The photo below is a good example of what information can be provided.

The box in the upper left corner of this photo shows the temperature range seen in the field of view, Cen 44.7 means the temperature in the white circle (middle of the photo) is 44.7°F.  The Max (57.9°F) or warmest temperature in the photo is in the far upper left-hand corner indicated by the red circle (barely seen) and Min (33.9°F) is the coldest area of the photo indicated by the blue circle.  Below the Cen, Max, Min box is the temperature scale showing how the temperatures in the form of colors are represented in the photo.  Moving across the bottom, 10:21 is the time the photo was taken.  °F indicates the temperature setting is in Fahrenheit.  The :0.97 is the emissivity setting, more on emissivity in a bit.  There is also a menu tab where adjustment to the camera can be made (this particular camera has a touch screen).  The far, upper right-hand corner shows the manufacturer of the camera, which happens to be Hikmicro.

Emissivity is a measure of how efficiently an object radiates heat.  Shiny materials reflect heat and have low emissivity whereas dark colored materials absorb heat and have a high rate of emissivity.  Be aware that viewing a thermal image of metal, mirrors or glass will reflect the heat of whatever is in the photo’s field of view, creating inaccuracies with the temperature readings.  If you need to accurately know the temperature of shiny surface, placing a black piece of tape on the object being measured will help.  Emissivity settings can be adjusted in the camera settings.  There are charts that can be found online with emissivity values of common building materials.

Level and span settings are just as important to understand as emissivity.  Level and span are a way to adjust the temperature range seen in the thermal photo.  Adjustments can be made either in the camera settings, before the photo is taken, or in the reporting software created by the camara manufacturer, after the photo is taken.  Narrowing the difference between the high and low temperature range can help to clarify what you are seeing in an image.

By reducing the temperature scale (the level and span scale is shown on right side of both thermal images), we can more easily see hot and cold spots in these images.  This manipulation of the photo was done in the reporting software.

Camera resolution and pixel count affect how clear a thermal image is.  The higher the numbers, the sharper the image.  My first camara only had a resolution of 60 x 60 with 3,600 pixels, the images were pretty blurry.  My Hikmicro Pocket 2’s resolution is 256 x 192 with 49,152 pixels, a huge improvement.  A high-end camera might have a resolution of 640 x 960 and more than 300,000 pixels.  Photos and videos taken with these cameras are very clear.  Of course, the price tag puts specialized cameras out of reach for all but professional thermographers.

Most entry level cameras will have focus-free lenses and fixed field of view.  As you move up in manufacturer’s product lines, cameras may have manual focus lenses offering more control and some even have interchangeable lenses.

Pallet is a color setting that can be adjusted in either the camera before taking a picture, or after in the reporting software.  Each of the manufacturers call their color settings by different names.  The photos below show a few of the many variations available in Teledyne Flir cameras.

A digital photo overlay in a thermal image helps show more detail.  This feature has different names depending on the manufacturer.  Teledyne Flir calls the feature Multi-Spectral Dynamic Imaging (MSX) and Hikmicro calls it Fusion.

Many thermal imaging cameras also provide a picture in picture option.  This can be shown with the thermal image in the center, or the digital image in the center with the thermal image in the surround.

Another option is to display the digital image separate from the thermal/digital image overlay.  The reports I submit to customers will include both the base digital image and the thermal image with digital overlay.  This can be helpful when it’s difficult to tell where the photo was taken when viewing just the thermal image.

You may also choose to blend the digital picture with the thermal image.  You can change the intensity or percentage of blending for the thermal overlay onto the digital photo.  This is typically done with the reporting software supplied by the manufacturers.  Another handy feature for helping to identify where the photo was taken.

Other Tips

It is important to understand how the sun shining on surfaces can affect an image.  This exterior photo was taken with outdoor temperatures at -10°F.  The left side of the home is shaded with the right side in full sun.  It’s also interesting how the shadows from the trees in the yard also affect the temperatures seen on the home’s siding.  Depending on how well this home is insulated, we may see some temperature variations transferred to the interior side of these exterior walls.

Thermal stratification is another phenomenon I see on occasion.  This is where we have a visually defined thermal break between warm air that has risen in a structure and cold air that has settled.  Be aware that sometimes what looks like stratification can actually be a change in the insulation (R-value) inside the wall or part of the assembly that contains a higher heat conductivity material, such as concrete or metal.

Damp and wet materials also show thermal differences, sometimes it can be hard to differentiate between an insulation issue and a wet surface.  These photos show two different thermal conditions.  The two square areas on the right are drying drywall patches.  The rest of the purple areas are from cold air moving into the wall cavities from the vented and unconditioned attic above.  This photo was taken during a blower door test.  You may need to use a moisture meter to confirm the presence of moisture.

Windows can be another area where thermal imaging can detect a problem.  Dual and triple pane glass used for windows and doors are usually sealed with a gas fill, typically argon.  If the gas escapes through a failed seal, the center of the glass will become cooler.  This can be detected by using thermal imaging.  Just remember that glass is reflective, be sure the image isn’t being affected by a reflection from inside the room.

Part of my job is working with homeowners who have high electricity consumption complaints.  I’ll use thermal imaging to quickly identify breakers or wires that have been drawing larger amounts of current.  Warm breakers or wires inside a service panel are often a tell-tale sign of higher usage.

One final piece of advice, have an expectation as to what you think the thermal image should look like before viewing the image on the camara or taking the picture.  As an example, if the temperatures are cold outside and warm inside, an air leak should look like the first image below.  Cold air during blower door testing is entering the heated home.  The opposite can also be true, blower door testing in warm weather with cooler interior temperatures should result in a photo as seen in the lower photo.  If you are seeing something else, you’ll want to investigate as to why.

Manipulating Images

Making changes to the camera settings before taking a thermal image photo can be done in the camera’s settings or menu, depending on your camera.  My Hikmicro Pocket 2 menu tab will allow me to make changes to the “image mode”, which includes thermal only, thermal with the digital photo overlay (fusion), picture in picture, or digital photo only (optical).  Pallet selection and the level and span options are also adjustable in the menu tab.  All changes are made using the touch screen.

The settings tab (to the right of the menu tab) is where you can change emissivity and distance to object settings and where you can set alarms for high or low temperature readings.  Device settings (unit, language, time and date) along with Bluetooth and other connection settings are also found in this menu.

Many of the viewing options in the menu tab can also be changed in Hikmicro’s reporting software, Analyzer.  Handy when wanting to make changes after the photo is taken.  This software is free to download on the Hikmicro website.

The key to understanding the settings menus in the camera and manipulating photos in the Analyzer software (or software from any of the other camera manufactures) is by simply making changes to the different options, become familiar with how these modifications can affect the image.

My thermal imaging cameras are my most used energy auditing and analysis tool.  Whether used to find missing or poorly insulated areas in walls and ceilings, detecting air leakage during a blower door test, pinpointing a water leak, or even exploring the temperature differentials in the world around me, they are an informational and fun tool to use.  With the reduction in cost and increase in performance, there should be no reason a contractor doesn’t have one in their tool belt.

This post first appeared in Fine HomeBuilding Magazine, issue #325-August-September 2024.