InterNACHI HEA key terms

The continuous layer of insulation and air control that separates conditioned interior space from unconditioned or outdoor space. Gaps or compression in this layer create bypasses that undermine the whole assembly's performance.

A path of comparatively high heat conductance through an assembly, such as a wood stud, steel framing member, or concrete slab edge. It lowers effective R-value and can cause cold interior surfaces and condensation.

The installed performance of an assembly after accounting for framing, fasteners, and other conductive bypasses. It is always lower than the nominal cavity insulation value and is the figure that should drive load and cost estimates.

The rated resistance printed on an insulation product label, measured for the material alone without framing or installation defects. It describes the product, not the wall, ceiling, or floor as actually built.

Squeezing of insulation into a cavity smaller than its manufactured thickness. It reduces R-value per inch and is common where batts are stuffed behind wiring, pipes, or roof sheathing.

Air movement through or across the surface of fibrous insulation, driven by outdoor wind or pressure differences, that strips heat from the material and lowers its real performance even when it looks intact.

The continuous system of materials that limits uncontrolled air movement between conditioned and unconditioned space. Its integrity is verified with a blower door test and it must be sealed at every penetration and joint.

Unintended flow of air through cracks, penetrations, and assembly joints, carrying both sensible and latent heat. It is often a larger energy and moisture problem than conductive losses in older homes.

Buoyancy-driven pressure pattern in which warm indoor air rises and escapes high in the building while outdoor air is drawn in low. It intensifies with height and indoor-outdoor temperature difference.

The plane at which indoor and outdoor pressure differences are actually resolved, typically the air barrier or the exterior sheathing. Diagnostic testing and insulation placement must respect where this plane truly is.

The temperature at which air reaches saturation and water vapor begins to condense. Locating the dew point within an assembly reveals where hidden condensation is likely to form.

The location inside an assembly where the temperature falls to the dew point of the surrounding air. Designers aim to keep this plane outside or on the warm side of moisture-sensitive materials.

A material that slows diffusion of water vapor through an assembly, rated by its permeance. Its correct placement depends on climate, and a poorly placed retarder can trap moisture and cause rot.

The rate at which water vapor passes through a material under a stated vapor pressure difference, usually expressed in perms. It distinguishes vapor-impermeable barriers from semi-permeable and permeable materials.

The ability of an assembly to release absorbed moisture to the interior or exterior. Designs that seal both sides of a wall or roof can eliminate drying paths and turn small leaks into serious damage.

The overall rate of heat flow through a window, door, or assembly, stated in Btu per hour per square foot per degree Fahrenheit. Lower values mean better insulating performance and it is the reciprocal of R-value.

The fraction of incident solar radiation admitted through a window as heat, ranging from zero to one. It drives cooling loads and should be selected together with U-factor, orientation, and shading.

Abbreviation for solar heat gain coefficient, the share of sunlight that becomes heat inside the building. Lower values reduce summer cooling demand, especially on west- and south-facing glazing in cooling climates.

A microscopically thin metallic film on glazing that reflects long-wave infrared radiation. It lowers U-factor and, depending on the surface it is applied to, can also tune solar heat gain.

The practice of closing unintended gaps with caulk, foam, gaskets, weatherstripping, and rigid covers. Priority goes to the attic floor, rim joists, and penetrations, and results are measured with a blower door.

The framing member at the perimeter of a floor system where the joists meet the foundation or band. It is a notorious leakage and thermal bypass location, often hidden behind insulation unless deliberately addressed.

Another name for the buoyancy-driven movement of air up through a building, causing infiltration low and exfiltration high. It explains why upper floors and attics often leak most in cold weather.

The space containing fuel-burning equipment and its air supply. It must have adequate combustion and dilution air, and its pressure must not be driven negative by exhaust fans or duct leakage.

Reversal of normal vent flow that pulls combustion products into the building instead of up the flue. It is caused by depressurization, blocked flues, or poor vent design and is a serious health hazard.

Combustion gases escaping from the draft hood or burner area into the room rather than exiting the vent. It can occur during startup or steady operation and is detected by flame or smoke testing.

A device on atmospheric combustion appliances that relieves excess draft and mixes room air with flue gases. It is also the point where spillage is observed during combustion safety testing.

A colorless, odorless gas produced by incomplete combustion that binds hemoglobin and can be fatal. Testing appliances and installing alarms near sleeping areas are core combustion safety measures.

Ventilation or flue flow produced by temperature and density differences rather than a fan. It is weak, weather-dependent, and easily overcome by building depressurization or tight construction.

A negative pressure inside a zone relative to outdoors or another zone, created by exhaust fans, duct leakage, or the blower door. It can reverse flues and pull soil gases or outdoor air inward.

A calibrated fan and gauge assembly mounted in an exterior doorway to pressurize or depressurize the house. It quantifies envelope leakage and, with zone doors, helps locate the leaks.

Envelope leakage normalized to house volume at a 50-pascal pressure difference, abbreviated ACH50. It allows comparison across homes and is used by weatherization and above-code programs as a threshold metric.

Cubic feet per minute of airflow through the blower door at 50 pascals of pressure. It is the raw leakage number from which ACH50 and estimated natural infiltration are calculated.

A small gauge placed over a receptacle, switch, or duct register to read the pressure difference across it while the house is pressurized. High readings flag likely leakage paths for targeted sealing.

Loss of conditioned air from supply or return ducts through joints, seams, and disconnected sections. Leakage in unconditioned space wastes energy and can pressurize or depressurize rooms and appliance zones.

A calibrated fan system that temporarily seals registers and pressurizes the duct network to measure leakage. Results are reported as CFM25 and often compared with total system airflow.

Duct leakage rate in cubic feet per minute at 25 pascals of test pressure. It is the standard duct tightness metric and is frequently expressed as a percentage of system fan airflow.

Use of an infrared camera to visualize surface temperature differences that reveal missing insulation, thermal bridges, air leakage, and moisture. Interpretation requires a sufficient indoor-outdoor temperature difference and steady conditions.

An instrument that measures pressure difference, commonly in pascals or inches of water column. It underlies blower door, pressure pan, and combustion appliance zone testing.

A measure of heating or cooling demand obtained by summing daily temperature departures from a base temperature. It normalizes energy use across weather so bills from different periods can be compared fairly.

Adjusting energy consumption for outdoor temperature differences so that bills from different seasons or years can be compared. It is essential before claiming that a retrofit saved energy.

Annual energy consumed per unit of floor area, often in Btu per square foot or kWh per square meter. It enables comparison between buildings and helps prioritize which homes offer the greatest savings potential.

The portion of energy use that stays roughly constant regardless of weather, such as water heating, refrigeration, and standby loads. Separating base load from seasonal load sharpens savings estimates.

Installed measure cost divided by estimated annual savings, expressed in years. It ignores measure life and fuel escalation, so it should be paired with lifetime cost-effectiveness analysis.

A judgment of whether a measure's lifetime savings justify its cost, using metrics such as savings-to-investment ratio or net present value. It guides which improvements a program can fund.

Ranking recommended improvements by savings, safety, durability, cost, and client goals. Health and safety items and envelope repairs typically precede equipment replacement and cosmetic upgrades.

The written list of measures, quantities, and specifications a contractor agrees to perform. It must match the audit findings and be specific enough to prevent substitutions or omissions.

The field document that translates approved scope into tasks, materials, and quantities for a crew. Clear work orders reduce callbacks and support verification that measures were actually installed.

Independent post-installation verification that work matches the scope and meets program standards. It typically includes visual checks, measurement of insulation depths, and sometimes repeat diagnostic testing.

A situation in which an auditor's judgment or recommendations could benefit themselves or an affiliated contractor. Disclosure and separation of audit from installation protect client trust and program integrity.

Obtaining a client's clear agreement to testing, data collection, and recommended work after explaining risks, benefits, and alternatives. It includes permission for combustion safety tests and access to private spaces.