Tips for effective testing
When homeowners look for ways to make their heating and cooling more energy efficient, often the first place they look is their mechanical system - furnace, heat pump, and/or air conditioner. Although the mechanical system is important, the real culprit may be as simple as air intrusion. Locating the trouble spots is critical to improving energy efficiency, reducing energy bills, and increasing comfort all year round.
"What surprised me was the amount of airflow out of the ducts"
"You can have the most efficient mechanical system on the planet and it doesn't matter if you can't retain the energy you're paying for within your four walls," says Brent Foster, owner and President of Northwest Infrared. Foster is a certified building analyst and building science thermographer in Olympia, Washington. He uses thermal imaging to find moisture issues and heat and energy loss in commercial, industrial, and residential buildings. His primary heat loss tracking tool is a Fluke Ti400 Infrared (IR) Camera.
Checking duct connections
In residential buildings, one of the biggest sources of air leakage is the ducted delivery system. As the conditioned air is pushed through ducts, it leaks into the unconditioned crawl space or basement at duct connections and at the metal "boot" that connects the ducts to holes in the floor.
In 2012, new residential provisions of the International Energy Conservation Code started requiring that duct and boot connection points be sealed. However, duct systems installed before that date - and there are millions of miles of them - don't have to meet that requirement. As a result, according to ENERGY STAR as much as 20 to 30 percent of the conditioned air flowing through duct work goes right into the crawl space or unconditioned basement.
"Until you get the envelope of the building efficient you've got nothing," says Foster. "You don't buy your way to efficiency. You measure your way to efficiency."
Locating energy loss
Figure 1. With a blower door installed, the infrared camera can help detect air leaks.
To locate heat lost through duct connections, Foster turns on the heating system to pressurize the air supply ducts. Then he takes his IR camera into the crawl space and scans the duct system. "With the infrared image, you can clearly see heat leaking out through the duct connections," says Foster.
The flip side of heat leaking out through the duct work is that cold air can come into the house through those same routes. When the wind blows, it depressurizes the building causing it to suck in air through every hole in the house. One of the main places that occurs is around the boot, resulting in cold air, mold, and moisture being drawn in from the crawl space.
To check the boot for leakage, Foster seals a "blower door" in the front doorway of a house (Figure 1) to depressurize the building. The blower door's power fan forces air out of the house, so that he can see the air leaks through cracks, window frames, door seals, and other gaps - including boot-to-floor connections - with the IR camera. "If there's a leak at the boot it will suck air past that connection that can be easily seen on the IR image," says Foster.
Figure 2. The dark blue area indicates massive air leakage past the bottom of an uninsulated door leading to the basement.
In a recent residential IR inspection that Foster conducted using a blower door, the homeowner was amazed to see how much energy was escaping through some less than obvious places. "I think most people expect to see missing insulation or air leaks around the windows so those things didn't jump out at me," says the homeowner. "What surprised me was the amount of airflow out of the ducts, and through an uninsulated and unsealed door that led to the basement (Figure 2). When the blower got going you could feel the wind just sucking out around the basement door."
For a new house, the current energy code requires that when the wind blows 20 mph there should be no more than 5 ACH (Air Changes per Hour). If the house meets that level and is still cold, Foster looks at the insulation. "I look at the amount of cold surfaces in the house which leads me to the insulation, or lack of it," says Foster. "Heat energy moves from hot to cold. So if you have a big section of wall that has no insulation and it's 70 degrees inside and 40 degrees outside, that heat energy is going to migrate to the cold surface."
To determine the level of insulation, Foster scans the walls, floors, and ceilings with the Ti400 IR camera. "I'm looking for cold spots - areas of the house, that weren't insulated or where the insulation is damaged and is no longer functional," says Foster.
Figure 3. The orange area indicates radiant energy on a hot summer day from the attic area above a bedroom due to limited insulatation.
A lack of - or damaged - insulation also shows up when the temperature is reversed - more like 80+ degrees outside and 60 to 70 degrees inside. Under those conditions the lack of insulation shows up in very hot images as illustrated in Figure 3.
Surveying the attic
Foster frequently finds gaps in attic insulation due to complicated roof lines that can prevent insulation installers from reaching some areas. Another common problem is attic insulation installed on the wrong surface. "Sometimes when I scan the ceiling of the floor below the attic, it appears that there isn't any insulation," says Foster. "When I take a look in the attic, I find that there is insulation, but it's installed directly underneath the roof sheathing rather than on the floor," Foster notes. "To be effective, insulation must be installed against the warm side of the wall or floor."
Foster relies heavily on IR scans to analyze the state of the insulation. "I can tell more about attic insulation from inside the house with an IR scanner than I can tell by physically standing in the attic, because with an IR camera I can get to every section of the attic from within the home," says Foster.
Completing the inspection
He uses the Fluke Ti400 camera because it has a lot of user-friendly features that make the job go faster, like a touch screen and push button operation that allows him to operate controls with his thumb. "I really like the speed at which I can set level and span with one button, take an accurate image and move on," says Foster. "It's not loaded with a bunch of features for show. The functions are very accessible and important to getting the job done accurately."
When the inspection is complete, Foster produces a report describing what he found, complete with IR images of problem areas and recommendations of how to resolve the problems. His business is strictly IR inspection; he doesn't sell any products or offer contracting services, so there is no conflict of interest.
In some cases homeowners can use the information from the inspection to do the repairs themselves, or at least decide what to do when. Says one homeowner: "Having the IR inspection helped me prioritize what needed to be done, rather than wasting thousands of dollars fixing things that aren't going to reduce my utility bills," he says.