BPI IDL key terms

Unintentional movement of air through gaps, cracks, and penetrations in a building envelope, driven by pressure differences from wind, stack effect, or mechanical systems.

Outdoor air entering a building through unintentional envelope openings, driven by pressure differences, adding to heating and cooling loads and affecting indoor air quality.

Indoor air escaping outward through unintentional envelope openings, carrying moisture and pollutants into wall and attic cavities where condensation and damage can occur.

A calculated equivalent open area that would produce the same leakage as the whole envelope at a reference pressure, typically 4 Pa, allowing comparison between buildings of different size.

Cubic feet per minute of airflow measured across the blower door fan while the building is held at 50 pascals of pressure difference, the standard single-point leakage metric.

The CFM50 leakage rate multiplied by 60 and divided by the building's conditioned volume, normalizing leakage for envelope size so buildings of different dimensions can be compared.

The chosen indoor-to-outdoor pressure difference at which leakage is reported, commonly 50 Pa for envelope testing and 25 Pa for duct testing, enabling consistent comparison of results.

The difference in static pressure between two locations, such as indoors and outdoors, that drives air through openings and is the physical quantity blower doors and duct testers manipulate.

The natural indoor-to-outdoor pressure difference present before or after a test, measured so it can be subtracted from readings to avoid bias from wind and stack effect.

The calibration step that sets the gauge to read zero while sensing the current baseline condition, so subsequent pressure readings represent the change caused by the test fan.

A calibrated variable-speed fan mounted in a temporary panel and door frame, used to pressurize or depressurize a building so envelope leakage and pressure boundaries can be measured.

A blower door procedure that exhausts air from the building to create negative indoor pressure, drawing outdoor air through leaks so leakage paths can be measured and located.

A blower door procedure that forces air into the building to create positive indoor pressure, useful for finding leaks by feel and for verifying duct leakage to outdoors.

A blower door or duct test that records airflow at several pressure differences, allowing a curve fit that yields leakage at a chosen reference pressure and the flow exponent.

A test that records airflow at one pressure difference and converts it to the reference pressure using an assumed flow exponent, faster but less precise than multi-point testing.

The exponent n in the power law relating airflow to pressure difference, typically near 0.65 for building leakage, describing whether openings behave more like cracks or large holes.

A plotted relationship of airflow versus pressure difference from multi-point testing, whose shape reveals leakage characteristics and supports extrapolation to the reference pressure.

The selection of a blower door fan's orifice ring, or no ring, to match expected airflow so the fan operates in a range where its calibration is accurate.

The manufacturer-supplied relationship between fan speed or pressure signal and delivered airflow, which must match the installed ring and be corrected for air density.

An adjustment applied to measured fan airflow for altitude, temperature, and barometric pressure, because calibration tables assume standard air density conditions.

Air escaping from or entering a duct system through joints, seams, and disconnected sections, wasting conditioned air and degrading pressure balance and indoor air quality.

The standard duct tightness metric reporting cubic feet per minute of leakage with the duct system pressurized to 25 pascals, a lower reference than envelope testing.

Leakage measured with all supply and return registers temporarily sealed and the duct system pressurized, capturing losses to both conditioned and unconditioned spaces.

The portion of duct leakage that escapes to unconditioned space, measured by pressurizing ducts while the house is depressurized so only outdoor-connected leaks register.

A procedure using a calibrated fan and temporary register seals to pressurize the duct system alone, measuring airflow needed to hold a set pressure such as 25 Pa.

A temporary cover placed over each supply and return grille during duct testing to isolate the duct system from the conditioned space so leakage can be measured accurately.

A hooded gauge placed over a register that reads the pressure difference across it while the house is depressurized, indicating the relative leakiness of that branch.

Measuring pressure differences between the house and attached zones such as attics, garages, or crawlspaces during a blower door test to judge boundary tightness and connectedness.

The continuous layer of insulation and air barrier separating conditioned space from unconditioned space, which must align with the pressure boundary for efficient performance.

The continuous air barrier surface that separates conditioned from unconditioned space and controls where pressure differences drive leakage; it should align with the thermal boundary.

The material or assembly, such as sheathing, drywall, or membrane, that resists air movement through the envelope and is the primary target of air sealing work.

The practice of closing unintended openings in the envelope with caulk, foam, gaskets, or membranes to reduce air leakage and improve comfort, durability, and energy performance.

Pressure differences created by buoyancy, where warm indoor air rises and escapes high in the building while outdoor air enters low, intensifying with height and temperature difference.

A small device producing a visible smoke trail used during a blower door test to reveal the direction and location of air movement through suspected leaks.

The written record of a test including conditions, instrument calibration, measured values, calculated metrics, and any limitations, supporting third-party verification and client communication.

Documented environmental and building state during testing, such as indoor and outdoor temperature, wind, baseline pressure, and whether doors, dampers, and registers were set as required.

Documentation that gauges and fans were checked against known references within the required interval, establishing that reported measurements are traceable and trustworthy.

Pre-test checks for combustion appliance backdrafting, blocked flues, and occupant hazards, because depressurization can pull combustion gases into occupied space.

Combustion gases escaping from an appliance or vent connector into the building rather than up the flue, a serious hazard that testing procedures must anticipate and avoid causing.