How a Blower Door Measures Building Air Leakage
A blower door creates a controlled pressure difference across a building enclosure. Measuring pressure and airflow together reveals leakage that cannot be judged reliably by appearance alone.
Follow the air through the process
Seal the fan into the doorway
In this depressurization example, a temporary panel seals around the fan while it moves indoor air outside.
Follow the replacement air
Outside air enters through the remaining enclosure gaps. At a stable test pressure, the fan flow reflects the leakage through the tested boundary.
Measure pressure and flow separately
One channel measures the indoor-to-outdoor pressure difference. A calibrated fan-sensing arrangement determines airflow; motor speed alone is insufficient.
Compare at the same pressure
After sealing a leak, adjust back to the same pressure difference. Less airflow at that pressure indicates reduced leakage.
Airflow function
- Create the pressure difference across the tested enclosure.
- Operate over the measuring system’s intended leakage-flow range.
- Integrate with the sealed housing, calibrated sensing arrangement and controls.
What can change the result
- An incorrect flow-ring setting can produce the wrong displayed airflow.
- Damaged tubing or misplaced flow sensors can affect the measurement.
- Comparing tests at different pressures can obscure the effect of sealing.
Start with the complete air path
Share your layout and the information you already have. Unknown values can be identified before a configuration is selected.
Match the fan to this air path
LONGWELL EC axial families may be considered as fan components for suitable OEM measuring-system development. Match the operating range and controls, then establish the measurement performance of the complete assembly.
Where it sits
Within an OEM-designed sealed fan housing connected to the measurement system. Flow rings, pressure sensing and the temporary door panel are separate assembly elements.
Why consider this configuration
A controllable fan component can be evaluated against the intended pressure and leakage-flow ranges. Measurement accuracy then has to be established for the complete sensing arrangement.
Check the result in your equipment
Application questions
Why measure airflow as well as pressure?
Pressure defines the test condition. The airflow required to maintain that condition describes leakage through the tested enclosure.
Why does the flow-ring setting matter?
The instrument converts the fan’s sensed pressure into airflow using the selected device and ring configuration. The setting must match the installed hardware.
Can a standard fan and its catalog airflow replace a blower door?
A measuring system needs a calibrated sensing arrangement. A standalone fan’s catalog rating does not establish installed leakage flow.
Discuss an OEM fan component
Share your housing concept, pressure/flow range and control requirements. Include the flow-ring and sensing arrangement and the plan to calibrate the complete instrument.
A layout, installation photos or your existing model is enough to start the discussion.