[Editor's note: This article assumes that readers know their way around an infrared camera for doing thermal imaging. If you're unfamiliar with these tools, please review Getting Started in Infrared. For basic information on using a blower door, please see Blower Door Testing]
Finding air leaks in existing homes can be a trying task. Driven by air pressure from inside and outside the building, air can sneak in through any crack or crevice in a building's envelope and move through any number of convoluted pathways within framing cavities. It's impossible to seal every hole in an existing building, so the real task is finding the most significant air leaks in order to tighten the home as cost-effectively as possible. But how do you identify which holes are the biggest leaks?
A simple inspection protocol developed for air-sealing homes under EmPower New York (a program providing energy retrofits and education to low-income New Yorkers) uses a thermal imager, a.k.a. infrared (IR) camera, in tandem with a blower door. The procedure involves comparing thermal images taken with and without a blower door running, and enables home-performance workers to differentiate air leaks from insulation weaknesses.
Robert Kahabka, owner of Northern Comfort Diagnostics, a home-performance contracting and energy training firm based in Elmira, N.Y., helped to develop the technique—one of several in Empower New York's "Advanced Air Sealing Protocol." Kahabka explains the thermal-imaging technique he uses as a simple three-step process.
- First, he views "static conditions" by scanning the building with the thermal imager but without the blower door running. This provides Kahabka with a "baseline" reading.
- Next, he uses the blower door to depressurize the building (the blower-door fan is pulling air from inside to outside) and leaves the blower door running. The goal is to pull air of a different temperature through the leaks in the building envelope.
- With the blower door running, Kahabka scans the building again with the thermal imager. This second scan gives him a sense of what is happening behind the drywall under "dynamic conditions."
By taking two similar sets of images—one set in baseline, or static, conditions, and another set in dynamic conditions—Kahabka can compare the two views. Any change in an image from the static to the dynamic viewing is probably related to air leaks. The procedure gives him the ability to see things going on behind the drywall and to find air leak pathways that may be occurring in areas where man cannot tread (literally).
Baseline Images
The first step is to scan the building before turning on the blower door. This is how most thermal imaging is done, and the goal is to find "insulation anomalies," as Kahabka calls them—areas of missing or thin insulation where conductive heat flow shows up on the screen of the infrared camera.
As with any thermal imaging, the bigger the temperature difference between indoors and outdoors, the better the image you'll get. But with today's IR cameras, all you really need is a 10°C—about 18°F—difference between indoors and outdoors.
Dynamic Images
After walking through each room of the building, scanning and saving a set of baseline images, Kahabka fires up the blower door to depressurize the building. The amount of depressurization is not important. What you want is to drag air of a different temperature through the leaks in the envelope, but you don't want so much pressure that the thermal image changes too fast, because it helps to see how it is changing as you move through the house the second time.
The examples throughout this article show photos taken on a fall day at a house in upstate New York. It was not particularly cold—around 50°F—and the indoors was about 70°F, giving Kahabka enough of a temperature difference to map the changes in indoor temperature as the blower door pulled in cooler outdoor air through leaks.
The comparison helped Kahabka identify the areas where air leaks were having a huge impact on the thermal integrity of the insulation. There was insulation in these areas, but when air was pulled through it, the insulation R-value visibly collapsed. Prime examples are in the office (see slideshow photos 5 and 6) and the kitchen (see photos below).
In the latter case, a surprisingly big leak allowed air to be pulled across a wide area of the ceiling. The fix for this is not a standard one: Kahabka will recommend that the ceiling be dense-packed with cellulose. Dense-pack insulation is not often seen as an air-sealing material, but it is an effective way to shut down the leak pathways for air that is probably coming from a network of framing gaps—now buried beneath roofing, siding, and exterior trim—created when an addition was built on the exterior wall of the kitchen.
These are the types of leaks a home-performance contractor needs to focus on. If he's not hitting these, but is doing things such as weather-stripping doors and windows, then he's missing large areas of the building frame that are functioning as leak pathways directly into conditioned space.
We may not be able to feel all the air leaks. We may not be able to see them. But under dynamic conditions with the blower door running, the infrared is telling us that when the wind blows outside, whole sections of the thermal envelope chill down to a temperature where condensation can form, where there's energy loss, and where there will undoubtedly be comfort issues.
In the kitchen, Kahabka scans the surface of the partition wall separating the kitchen and the garage and (at the ceiling) a joist system between two stories of the building. The building is still in static conditions, and as he scans this area, he sees clear definition of the ceiling/floor framing.
Surprisingly, he also sees strong discoloration—a clear indication that this area is cooler than other areas within the building. He's beginning to pick up areas of deeper coolness where air leaks or lack of insulation—he can't tell which yet—are creating a serious change in temperature, visible as bright blue bands in a sea of warmer surface temperatures. If this image changes, he will be able to attribute the colder surfaces to air leaks. But if it stays relatively unchanged, it's probably an insulation anomaly.
In fact, when Kahabka scans again with the house in dynamic conditions after the blower door has been running a few minutes, the answer comes to light. There is a tremendous amount of change from the baseline infrared image—the deeper blue is caused by air leaks.
Where the dark blue has feathered down the wall, air has completely permeated the insulation and destroyed the thermal integrity of the exterior wall. This is the kind of air leak that can result not just in energy loss, but in serious condensation problems, and Kahabka predicts that when occupants sit at the breakfast bar below this area of the ceiling in the deep of winter (the house is near Syracuse, N.Y.), they feel the cold. Even if the air is not entering the room and creating a draft, the chilled wall and ceiling create a large cold surface that is literally sucking the heat from the occupants' warm bodies.
The fix Kahabka will recommend for this is somewhat unconventional— unless you move in weatherization circles. He will suggest densepacking the ceiling bays in this area. The dense-pack cellulose insulation will shut down the leak pathway from the interface between the addition and the main house that connects with this ceiling. It is probably the only way to access the leaks causing this.
Clayton DeKorne is JLC executive editor. Robert Kahabka owns Northern Diagnostics, in Elmira, N.Y. Special thanks to Kelvin Keraga of EmPower New York and to the team at Learning Solutions Winstanley for their assistance with the images in this article.
