Can a Thermal Camera See Through Walls?

October 09, 2019

Thermal camera on Metal door

Can Thermal Cameras See through Walls?

No. No thermal camera can see through a wall or any solid object. The common misconception is that thermal camera can see heat and nothing else therefore if there is a heat source behind a wall or solid object it should pick up the heat. Fortunately, this isn’t the case as only the heat on the surface is what any thermal camera picks up. Still confused? Not to worry, we’ll do in depth about this topic and we will start with a little history. 

 

The History of Thermal Camera

Let’s face it, a thermal camera is a league of its own - outclassing even the most sophisticated of cameras in more ways than one. Ever since its inception, its initial use in the U.S. military (e.g., Korean War) and its late adoption in firefighting in 20th-century America, the thermal imaging device has without a doubt produced groundbreaking results - eclipsing any point-and-shoot camera on the planet in revealing the unseen.

The Evolution of the Thermal Camera: Through Thick and Thin

Thanks to astronomer Sir William Herschel (1738-1822), infrared was discovered. Using a thermometer, Herschel, the astronomer whose claim to fame incidentally is his discovery of the planet Uranus, stumbled upon a dark region beyond the red end of the color spectrum produced by sunlight in his prism experiment, a replication of the testing done by Isaac Newton. To his surprise, the region under study was not only hotter than the rest but was also invisible to the naked eye.

Of course, we now call that spectrum as the electromagnetic spectrum and we know that in that spectrum, temperature readings increase s the color changes from violet end of the spectrum to the red end. Today, the thermal camera stands unchallenged as the foremost device to measure the presence of infrared light - aptly called ‘thermal energy’ - in various degrees. Seeing the immense benefits, it did not taking long for the military to quickly pounce on infrared technology. 

A century or so later since Herschel’s experiment, thermal imaging was actively used in modern warfare - to gain a distinct advantage over the enemy. Some key milestones:

In 1929, an infrared-sensitive electronic television camera was used as part and parcel of the British anti-aircraft defense system. Years later, not to be outdone, American soldiers made the most out of thermal imaging cameras during the Korean War (1950-1953).

Steadily, infrared imaging technology was getting lighter with the ultimate goal of being able to use it on the move. Just about anywhere. And with thermal camera’s supreme ability to detect heat and all its intensity even with all the smoke, it was just a matter of time for the device to fall into the hands of firefighters in the American mainland. For their part, the American Society of Non-Destructive Testing soon developed teaching standards for thermal imaging courses starting in 1992. Eventually, by 2006 prices of thermal cams fell through allowing home inspectors - amongst them HVAC and electrical experts - to use them professionally.

How does thermal imaging camera work?

Thermal imaging camera, also known as a thermal camera and also known as an infrared camera or IR camera, renders infrared radiation as visible light. In short, these powerful devices detect heat. Specifically, they detect heat as it bounces off an object. Therefore any thermal energy behind a wall is thus bounced back from that side and not through the wall, but in some cases thermal cameras can see heat on a wall where the source is on the other side. 

Lets go over in detail what a thermal camera can or cannot see through

 

image split in half with left side in darkness the right side showing white image of man in forest

The Dark

In areas where there is an absence of light thermal cameras can operate just as well as if it was in normal lighting conditions as it doesn’t require any visible light to function. This is the fundamental reason why security and police force across the world were quick to adopt this technology. Standard surveillance cameras don’t operate well in the dark and criminals are quick to hide in dark dense locations. A thermal camera will have no problem picking up any part of a human body not blocked by a dense solid material. 

image on left showing smoke filled corridor, thermal image on the right revealing fire

 

Fog or smoke 

In both thick heavy fog and smoke a thermal camera is able to pierce through it and get a reading on the thermal radiation that might occur past or in it. This is because commercially-available thermal cameras operate on two fronts: Long-wave infrared (LWIR) and Mid-wave infrared (MWIR). We’re talking about 3µm to 14µm wavelengths in the electromagnetic spectrum. MWIR spectrum is at 3 to 5μm in wavelength while LWIR is at 8 to 14μm in wavelength. And, if not all, objects on the planet emit their heat in these ranges.

The hotter an object gets, the more it puts out electromagnetic radiation or EM. However, the smoke and fog particles are significantly smaller than the wavelength of infrared and therefore does not block their radiation. Read can read more about how fire fighters use thermal cameras here

 

table and chair indoors on the left, thermal image showing heating behind walls on the right

A Solid Wall

As explained at the start of this blog, thermal cameras of any kind cannot see through a thick solid and well insulated wall. Now, emphasis on thick and insulated. Why? That’s because in several different situation a thermal camera will see like its can detect thermal radiation through a wall. 

If a there is a cold or hot heat source on one side of the wall and it is strong enough to change a part of the walls temperature, this can be picked up. For example, you are looking at the ceiling of your kitchen which happens to be located underneath your bathroom. You don’t notice anything out the ordinary when looking at it with your naked eye but through a thermal camera you may notice a patch that's colder than the rest. The reason? You have a small barely detectable leak from your bathroom and its slowly collecting up but isn’t in sufficient quantity to cause any real damage, and its cold water that's leaking. The water is soaking into the ceiling and causing its temperature to be lower than the rest of the leak free ceiling therefore it is showing up on the thermal camera. 

 

hand on wall to feel the heat

You can think of it this way, if you were to place your hand on a wall or other types of solid object and you can feel heat or cold from a source from the other side then a thermal camera is showing exactly what you are feeling but it can do it so much better. 

Now, thick walls or well insulated walls do not conduct heat and therefore would likely block out any heat sources completely, which is normally the primary purpose for insulation. It gets a little but more tricky with some metal surfaces and glass. With shiny and smooth metal surfaces it will end up acting like a mirror and reflect the heat 

 

Why you need a thermal camera to see through walls

You might be wondering now that if its a simple as seeing the heat is the same as using my hand then why would I need to spend money on this device? You’re not wrong in this way of thinking but consider my leak analogy. How often do you touch your ceiling or walls to check for temperature changes? Even then when the damage is quite small at the beginning the small variation in temperature may be so small you wouldn’t notice. 

This is where the thermal camera truly shines. It is so sensitive that small temperature changes will be as clear as day through it. Locating leaks and abnormal temperature early on is critical in saving systems and preventing further damage. 
thermal camera showing exact spot of problem vs taking the whole floor apart

Furthermore, suppose you had an inkling of a leak happening, where would you begin to open up the boards or punching a hole through a wall to find overheating electrical components? The thermal camera will point you in the right direction and save you time and money. 

 

So can It Let You See Through Walls?

That is the one-million-dollar question. And the answer will get right back at us by looking at infrared’s unique characteristics. Looking into how infrared light behaves is paramount to unlocking the capabilities of thermography.

First up. When we use the language ‘see’, we are referring to the capacity of our eyes to view the world we live in. The mountains, the leaves, etc. We love old-school cameras as they give us an exact - if not better - rendering of the world around us. A world dependent on light to be seen.

But a thermal camera does not work that way. It does not see as our eyes can see. Instead, it detects heat around it - individualized as heat signatures. So when looking at a thermograph, the picture produced by thermal imaging, you see colors representing various thermal energy in its environment.

What the thermal camera see therefore is not how an ordinary camera would see. In its world, objects are defined by how much heat energy it is emitting. Thus, it can only register thermal energy bouncing off an object in front of it.   

So when scanning a wall, a thermal cam detects the heat bouncing off that wall. The surface temperature changes of the perpendicular barrier so to speak. So if something so hot, like fire, is behind that wall, the heat of that fire will register on that wall. And the thermal camera will see it. The heat caused by that proverbial fire would be seen on the resulting thermograph.

 

Strictly speaking, infrared is capable only of detecting the heat signatures of the surfaces in front of it. So the answer to that layman’s question is a resounding NO. That’s only because the question is posited from the POV (point of view) of seeing as humans would. From the perspective of the thermal camera, however, we can say it can see through walls. And the answer is YES. That’s because it can detect heat behind the wall that’s affecting the wall. Again, this is in reference to the fact that heat is the language of thermography. And not the beautiful sceneries we look for in a traditional picture.

 

Common Thermal Camera Uses 

Thermal cameras have advanced so much since its inception. There are many added features to enable them to better connect to other devices via wifi and bluetooth and some of the latest advance uses of them is to fit them onto drones. 

Here are just some of the existing applications where they are used;

  • Home Inspections - Find problematic insulation, locate water leaks and damage
  • Electrical inspection - Identify defective parts and replace or fix before it affects the entire system
  • Police Force - Car chases at night and searching through vast fields of bush and forestry at night to find run away suspects
  • Security - Home and office security for effective night time surveillance 
  • Manufacturing - 24/7 monitoring of production lines for defective products and malfunction components
  • Medical and Veterinary - Check for inflammation or damage to flesh in animals and humans. 

 

To conclude

Does a thermal camera see through walls? The answer will depend on what kind of picture you want. Your POV, so to speak. From the perspective of producing a picture of the objects, the same kind picture you keep on your smartphone as memories, behind that wall, it would have to be a NO.

Bear in mind, however, that at its essence an infrared camera sees only heat signatures. Unlike an ordinary camera. So if the question is rephrased to: Can a thermal imaging device see the heat behind a wall? And the answer is it’s entirely POSSIBLE. So long as that heat signature is strong enough to affect the surface temperature of that particular wall.

Again, all these emphasize how a thermal camera has made a huge dent in our daily lives - wall or no wall. 

 

Check out our range of thermal cameras here and if you are interested in learning more about thermal cameras including what to look for check out our thermal camera guide here

 

Watch our video here:

 

Sources:

https://www.nachi.org/history-ir.htm





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