Leaky joints succumb to thermal imaging

How do you find the energy leaks in a super-efficient house? Increasingly the answer is thermal imaging, as builders wise up to plugging obvious air leaks.

That was the case recently as the Zero Energy Idea House built by Shirey Contracting in Bellevue, Wash. underwent pressurized blower door tests and a thermal imager inspection. Energy audit professionals from Fluke Corp. worked with the Washington State University (WSU) Extension Energy Program to perform the tests.

The demonstration house is more than three times as efficient as the standard for Energy Star homes. Said Donna Shirey, owner of Shirey Contracting. “Reducing airflow in a house is one of the best ways to conserve energy, and here we have built a home that exchanges air only twice every hour. Compare this to the average new construction home which exchanges air about 10 times an hour; an old home which has about 20 air exchanges per hour; even an Energy Star qualified home needs to be just under 7.0. At 2.0 we think we are looking really good.”

Thermal imaging uncovered a few unexpected areas of potential energy loss. There was some minor air infiltration around the windows and doors as well as around one electrical lighting box. The imaging also exposed problems at a few joints: where a support beam meets the back wall, in the space between a downstairs ceiling and the floorboards above, and where a support beam had been enclosed near a ceiling.

“Finding air leaks in a home this efficient is not simple,” said Michael Stuart, Sr. Product Marketing Manager at Fluke and certified Level II Thermographer and infrared energy auditor. “But the sensitivity to temperature variation provided by thermal imaging technology makes little things much more apparent. Without an imager, it would be much more difficult to find all the leaks and nearly impossible to accurately document them.”

After minor repairs, Shirey Contracting is shooting for a new milestone -- an air exchange rate of 1.5 or better.

Thermal testing for buildings like the Zero Energy house starts twenty-four hours before the inspection, when all known penetrations in the building envelope are closed (including windows, doors and vents). Radiant space heaters then go inside the closed-up house to heat and stabilize the inside temperature at a high level, so there would be enough temperature differential between inside and outside in time for the inspection. (When the Zero Energy house was inspected, the outside air temperature was 60°F. The interior air temperature was approximately 88°F. Most accepted standards require temperature differences of at least 18°F for best results.)

A blower door goes on the front entry door, and the house is depressurized, blowing the interior air out through the front doorway. As a result, cool air from outside the house enters the building envelope through other areas, trying to fill the vacuum created by the process. At the Zero Energy house, Fluke thermal imagers then could detect where the air was entering unexpectedly with particular attention to windows, doors, and other areas penetrating the building envelope. Infrared and visible images were captured and saved for the creation of an official report.