A blower door is a tool used by an Energy Auditor which lowers the air pressure inside a building, allowing outside air to flow in through all unsealed cracks and openings.

Blower doors consist of a frame and flexible panel that fits in an exterior doorway, a variable-speed fan, a pressure gauge to measure the pressure differences inside and outside the home, and instruments for measuring airflow.

Blower doors are either calibrated or uncalibrated. The latter can only locate leak paths in a home, but can’t measure the overall tightness of the building, expressed in air exchanges per hour. Use of a calibrated blower door is preferred, and will provide data that quantifies the amount of air leakage and the effectiveness of air-sealing.

Borate is a naturally occurring mineral additive used to give cellulose insulation its Class A fire rating. The borate, as fine as sugar at the start of the manufacturing process, is further milled to a particle size comparable to smoke, and is infused in the cellulose fiber. National Fiber uses an all-borate formulation, as opposed to a borate/ammonium sulfate mix.(See Ammonium Sulfate)