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Chapter 1
Introduction
1.1 What is a Blower Door?
The Blower Door is a diagnostic tool designed to measure the airtightness of buildings and to help locate air
leakage sites. Building airtightness measurements are used for a variety of purposes including:
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Documenting the construction airtightness of buildings.
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Estimating natural infiltration rates in houses.
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Measuring and documenting the effectiveness of airsealing activities.
•
Measuring duct leakage in forced air distribution systems.
The Blower Door consists of a powerful, calibrated fan that is temporarily sealed into an exterior doorway. The
fan blows air into or out of the building to create a slight pressure difference between inside and outside. This
pressure difference forces air through all holes and penetrations in the exterior envelope. By simultaneously
measuring the air flow through the fan and its effect on the air pressure in the building, the Blower Door system
measures the airtightness of the entire building envelope. The tighter the building (e.g. fewer holes), the less air
you need from the Blower Door fan to create a change in building pressure.
Figure 1: Blower Door Depressurization Test
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Chapter 1
Introduction
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