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Thermal Imaging

We got our first experience with thermal imaging during the LEED certification phase of our house construction, when our LEED green rater came through and took thermal images of the house interior when construction was nearing completion. He did find a few problem areas, including this region of the cottage wall where the insulation had settled as indicated by the blue horizontal band in the second image below:

We fixed that problem by blowing more cellulose insulation into that section of the cottage wall through a hole cut from the outside. Since then we've had a sense that some areas of the house were cooling more rapidly than they should, and more rapidly than they did the first winter, but it was hard to pin down any particular problem without being able to see inside the walls. Instead of paying our green rater to come back and take more thermal images, we decided to purchase our own thermal camera. This way we can do a more detailed analysis and re-check for problems at any time, and we can easily compare the thermal images before and after we take any corrective action. After researching the available options, it was apparent that FLIR was the most popular brand of portable thermal camera. FLIR makes a wide range of thermal cameras, with the most affordable being their i-Series. You can follow the links in the table below to see current prices on and even these 'affordable' imagers are not cheap, but we estimate that the camera we purchased will pay for itself in energy savings within about 8 years and the payback would be much faster in a more typical house with higher heating and cooling costs.

Model FLIR i3 FLIR i5 FLIR i7
Image Size 60 x 60
3,600 pixels
100 x 100
10,000 pixels
140 x 140
19,600 pixels
View Angle 12.5 degrees 21 degrees 29 degrees
Example Image


As you can see in the table above, the important difference between these three models is the image size. Each camera actually sees the same level of detail but with a smaller sensor size it's a bit like having tunnel vision, so you need to pan the camera around in order to see details over a large area. The larger sensor gives a wider view angle that lets you capture an entire scene or larger area of wall in a single image. We chose the FLIR i5 model as a compromise between price and resolution, and it's worked out well for our purposes. The less expensive FLIR i3 would work nearly as well for spotting problems, but its smaller images wouldn't work as well for publishing reports like this one.

Once we had our new thermal camera charged up, we switched it on and pointed it at a wall and our problem was immediately obvious! The two photos below show a section of outside wall in one of the bedrooms, first as a visible image and second as a thermal image (these were taken with two different cameras so they don't match precisely, and the second photo shows a slightly smaller region of the wall).


We can see a large cold band about 14 inches high along the top of the outside wall, where the wall surface temperature is about 6 degrees F cooler than it is below. The image even shows the locations of the wall studs behind the drywall. With the thermal camera we can see similar cold areas around all of the outside walls so it's very clear that our insulation contractor did not install the cellulose to the "dense-pack" density that we specified, and the insulation has settled very significantly leaving large areas of the walls completely uninsulated. Fortunately we can fix this, now that we can see the problem, but we'll do the work ourselves because that insulation contractor was not only incompetent but also extremely rude and we won't allow him on our property again.

Next - see before and after thermal images for Fixing Insulation Problems.