Title: Unit 4 Glossary
Course: HAC 140 Weatherization > Section: HAC 140 Weatherization

Unit 4 Glossary

Terms

Term | Definitions
Air changes per hour (ACH) | The number of times in one hour that all of the air in a home is replaced by outside air through air leakage and/or ventilation.
Building tightness limit (BTL) | A level of air tightness at which indoor air quality and building integrity may be compromised if the residence is any tighter.
Can’t reach fifty (CRF) | A factor that extrapolates air flow at lower pressure differences to air flow at 50 pascals pressure difference. Used in blower door diagnostics when the shell is too leaky to allow the blower doo ...
CFM50 | Measurement of air leakage in cubic feet per minute at 50 Pa pressure difference.
CFMnatural | Amount of air leakage in cubic feet per minute under natural conditions.
Cubic feet per minute (CFM) | A measurement of air movement past a certain point or through a certain structure. Used in pressure diagnostics to quantify air leakage.
Low-flow rings | Part of a blower door that forces air past the sensors fast enough so that a reliable reading can be obtained.
Manometer | A measuring device for small gas pressure differences.
Minimum ventilation requirements (MVR) | Lowest level of ventilation that will be acceptable to human occupants and that will minimize the potential for adverse health effects. This level may be measured using ASHRAE Standard 62.2.
N-factor | Used to convert readings taken at CFM50 to CFMnatural, the amount of air leakage that occurs naturally. The N-factor depends on climate, building height, and shielding from wind. N ranges from 9.8 ...
Pascals (Pa) | Metric standard for measuring pressure differences. 248 pascals equal one inch of water column, approximately the weight of one Post-it note.
Stack effect | The term describes the effect of higher pressure at the top of a structure, lower pressure at the bottom of a structure, and neutral pressure somewhere in between, relative to the ambient (surroun ...
Wind effect | A driving factor of pressure differences. The leeward, or sheltered, side of the home experiences negative pressure. The exposed side, positive pressure.
Winter mode | Closing off all exterior openings of a home and opening interior doors. Generally performed prior to doing a blower door test.
With reference to (WRT) | Compared to another measurement. In weatherization, a way to assess pressure differences between ducts and the rest of the home.
Worst case CAZ testing | A safety test, performed by specific procedures, designed to assess the probability of backdrafting in the home.