BPI BSP key terms

A way of viewing a home as interconnected parts-enclosure, occupants, mechanical equipment, and outdoor environment-where a change to one part, such as added insulation, alters pressures, moisture, and comfort somewhere else.

The part of a building that is intentionally heated or cooled for people to live in, and is therefore meant to be separated from attics, crawlspaces, garages, and outdoors by thermal and pressure boundaries.

The continuous layer of insulation and air sealing that separates conditioned space from unconditioned space and slows heat loss or heat gain through the building enclosure.

The continuous layer of air-sealing materials-drywall, sheathing, sealants, gaskets-that separates conditioned space from outside or unconditioned space and limits air movement across it.

Heat transfer through solid materials by direct molecular contact, moving from warmer to cooler regions, as when heat travels along a wall stud or through a window frame.

Heat transfer carried by moving air or fluid, including looping currents of air that rise along a warm surface and fall along a cool one, spreading thermal energy around a room.

Heat transfer by electromagnetic waves that moves through space without a medium, warming surfaces that absorb it, such as a person feeling warmth from a sun-heated wall.

Upward air movement caused by indoor air being warmer and lighter than outdoor air, which draws air in near the bottom of a house and pushes it out near the top.

Pressure on a building created by wind, positive on the windward side and negative on the leeward side, driving air in through openings on one face and out the other.

The height in a building where indoor and outdoor pressures are equal, dividing the enclosure into an upper zone that normally pushes air out and a lower zone that normally pulls air in.

Unintentional outdoor air entering a building through leaks in the enclosure, carrying heat, moisture, and pollutants with it and increasing heating and cooling loads.

Unintentional indoor air escaping through enclosure leaks, which wastes conditioned air and can carry moisture into wall and ceiling assemblies where it may condense.

The movement of water vapor through materials from higher vapor pressure toward lower vapor pressure, driven by moisture concentration rather than by bulk airflow.

The wicking of liquid water through porous materials such as concrete, brick, or wood, allowing moisture to move sideways or upward against gravity into building assemblies.

The temperature at which air becomes saturated and water vapor begins to condense into liquid, often on cold surfaces such as windows or hidden sheathing in a wall cavity.

The water vapor present in air shown as a percentage of the maximum that air could hold at that temperature; it climbs as air cools even when the moisture content stays the same.

A measure of a material's resistance to heat flow; higher numbers mean better insulating performance, and the value depends on thickness, density, and how well it is installed.

A measure of how much heat passes through an assembly each hour per square foot per degree of temperature difference; it is the reciprocal of the assembly's total R-value.

Heat flow that bypasses insulation through more conductive materials such as wood studs, steel framing, or concrete, lowering the effective R-value of the whole assembly.

A continuous material or assembly that blocks air movement between conditioned and unconditioned space; joints, penetrations, and intersections must be sealed for it to perform.

A material that slows the diffusion of water vapor through an assembly; whether it is needed and where it belongs depend on climate and on how the assembly gets wet and dries.

The work of closing unintended gaps, cracks, and penetrations in the pressure boundary using caulk, foam, gaskets, or weatherstripping so that air leakage is reduced.

A diagnostic test using a calibrated fan mounted in an exterior doorway to depressurize the house, measure total air leakage, and help locate leaks using smoke or infrared imaging.

Air changes per hour at a 50-pascal pressure difference, computed from blower door results; it normalizes measured leakage to house volume so different homes can be compared.

Annual fuel utilization efficiency, the percentage of fuel energy a furnace or boiler turns into useful heat over a typical year; higher ratings mean lower operating cost.

Seasonal energy efficiency ratio, a rating for air conditioners and heat pumps that divides seasonal cooling output by seasonal electricity input; higher numbers indicate greater efficiency.

Heating seasonal performance factor, a rating of a heat pump's heating efficiency over a season, calculated as heat output in Btu divided by electricity input in watt-hours.

Conditioned air lost from, or outdoor air pulled into, ducts through gaps at joints and connections, which wastes energy and can create pressure imbalances that affect combustion appliances.

The industry standard setting minimum whole-building and local exhaust ventilation rates for homes, based on floor area and number of bedrooms, to protect indoor air quality.

A balanced ventilation device that exhausts stale air while bringing in fresh outdoor air, transferring heat between the two streams to reduce the energy cost of ventilating.

A strategy that uses bath or kitchen fans to pull stale air out, with makeup air drawn in through enclosure leaks; simple and inexpensive, but it can worsen pressure and moisture problems.

The efficiency rating for water heaters, comparing the energy delivered as hot water with total energy consumed during a standardized test; higher values mean a more efficient unit.

The space containing fuel-burning equipment such as a furnace or water heater, where an adequate air supply and controlled pressures are needed to keep venting reliable.

A condition where combustion gases are pulled down the flue and into the house instead of venting outdoors, usually caused by house depressurization or a blocked or undersized chimney.

Combustion gases escaping from an appliance's draft hood or burner area into the living space rather than traveling up the vent, often found with flame or smoke testing.

An odorless, colorless gas produced by incomplete combustion that can cause illness or death; proper venting and testing of fuel-burning appliances are essential safeguards.

A calculated ceiling on how leaky a house can be while still allowing enough natural air movement for its combustion appliances and occupants; blower door results are compared against it.

A radioactive soil gas that can seep into a home and accumulate indoors, raising lung cancer risk; testing is the only reliable way to know if mitigation is needed.

Fungal growth that requires moisture, nutrients, and suitable temperatures; it can stain surfaces, damage materials, and contribute to odors and health complaints in damp buildings.