A blower door is used to determine a home’s overall leakiness as well as to pinpoint specific leaks. A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure flows in through all unsealed cracks and openings. While conducting a blower door test, a smoke pencil or infrared camera may be used to detect air leaks. These tests determine the air infiltration rate of a building.

Thermography, or infrared scanning, is used to detect thermal defects and air leakage within building envelopes. Thermography measures surface temperatures by using an infrared camera to see light that is in the heat spectrum. Images taken by the camera record the temperature variations of the building’s skin ranging from white for warm regions to black for cooler areas. The resulting images help us determine where heat is escaping.

A thermographic inspection is either an interior or exterior survey. Interior scans
are more common, because warm air escaping from a building does not always move through the walls in a straight line. Heat loss detected in one area of the outside wall might originate at some other location on the inside of the wall. Infrared imaging can also detect moisture that is undetectable to the naked eye, which will prevent water damage.

Infrared scanning and blower doors are often used simultaneously. The blower door helps exaggerate air leaking through defects in the building shell. Such air leaks appear as black streaks in the infrared camera’s view finder.