An infrared camera is not much use in a new house under construction, until the house is insulated. But once the house is being heated or cooled, the camera becomes a helpful troubleshooting tool. The temperature difference between the indoor space and outside needs to be about 20°F or more, so the camera has something to look at. In a completed house in our upstate New York market, the device is useful in summer or winter (about eight months of the year). In mild spring or fall weather, we leave the infrared camera at the office. In this column, I’ll present a few odd cases that I’ve collected during home performance audits. Each example includes one visible-light snapshot and one infrared image. In most of the examples, I’m using the infrared camera in combination with a blower door during cold weather—putting the house under a negative pressure to draw cold outdoor air in through any leaks and identifying cold spots (blue and purple areas) with the camera.


In the above example, the visible-light image shows what looks like just a blank wall. But behind the wall is the bump-out for what we call a “doghouse fireplace.” The owner elected not to install the actual fireplace until later. A purple ghost image reveals the cold box where the fireplace would other-wise be. The wall is probably insulated to code, but there’s no air barrier on the other side. A small vented shed roof on the doghouse is letting in the wind, and cold air is blowing through the fiberglass onto the drywall (and into the room through TV-cable and power receptacles). This flaw is difficult to fix as a retrofit, but during construction, the wall could easily have been sheathed to protect the insulation on all sides.


The images above show a dropped soffit with two recessed light fixtures in it. In the infrared image, the lights are glowing with heat because they had just been turned off. The blower door is sucking in cold air (purple), because the top of the soffit is open to the cold attic above. A visual inspection of the attic wouldn’t reveal this flaw, because there’s insulation covering the hole. But the camera sees the cold air leak. To fix it, we went into the attic, pulled back the insulation, and air-sealed the opening with rigid foam and caulk. In new construction, drywalling the ceiling before framing down is a good way to maintain the air barrier.


A ceiling makes a good air barrier, but only if it’s airtight. Drywall works well, but other materials may not. The example above shows a ship-lap beadboard ceiling on an old porch that has been enclosed and conditioned. In the infrared image, the blower door is pulling in cold air through the cracks between the boards. The leaks show up as purple. In this case, we had to climb into that attic, vacuum out all the insulation that was in there, and apply a flash coat of spray foam. Then we blew in more insulation on top of the foam, keeping the insulation blanket in contact with the air barrier.


In one house, we discovered air infiltration at the bottom of a concrete basement wall (above). This is a high-performance house under construction, built with insulating concrete forms (ICFs); the images were taken in the walkout basement. You can see the Zehnder energy recovery ventilator (ERV) at left in the visible-light photo. With the blower door on, the infrared camera detected cold air seeping in at the base of the ICF wall—coming in through the footing joint (via perforated foundation drain tile set in gravel and draining to daylight). To fix the leak, we had to seal this perimeter joint with 6-inch-wide Tescon Vana tape.


Here’s an odd case: This thermostat (see photo, above left) controls in-floor radiant heat for the room; the story above also has radiant heat. The homeowners complained that this room was always cold, but after several callbacks, the HVAC contractor couldn’t find anything wrong. The thermal image reveals that the tubes supplying an upstairs loop run right behind the lower room’s thermostat. If the upstairs heat is on, this thermostat serving the downstairs room never calls for heat! This mystery might never have been solved without infrared imaging.