A blower door is a powerful fan that a trained energy professional temporarily mounts into the frame of an exterior doorway in your home. After calibrating the device, the fan pulls air out of the house, lowering the pressure inside. The higher outside air pressure flows through all unsealed gaps, cracks, and openings such as gaps, cracks, or wiring penetrations. If conditions do not allow for lowering the pressure in the home, the fan may also be operated in reverse, increasing air pressure inside the house.

While the blower test is being conducted, the analyst may use an infrared camera to examine the walls, ceilings, and floors to find specific locations where insulation is missing and air is leaking. The analyst may also use a nontoxic smoke pencil to detect air leaks in your home. These tests determine your home's air infiltration rate, recorded on a laptop or tablet.

The blower door test is part of your home's energy assessment. Your contractor may also operate the blower door while performing air sealing (a method known as blower door-assisted air sealing) and after measuring and verifying the level of air leakage reduction achieved.

Blower doors consist of a frame and flexible panel that fit in a doorway, a variable-speed fan, and a digital pressure gauge to measure the pressure differences inside and outside the home, which are connected to a device for measuring airflow, known as a manometer. 

There are two types of blower doors: calibrated and uncalibrated. Auditors must use a calibrated door with several gauges that measure the air flowing out of the house through the fan.

Uncalibrated blower doors can only locate leaks in homes. They do not provide a method for determining the house's overall tightness.

The data from the calibrated blower door allow your contractor to quantify the amount of air leakage before installing air-sealing improvements and the reduction in leakage achieved after air-sealing is completed.