How is a duct static pressure test conducted in principle?

How is a duct static pressure test conducted in principle?

• A. Use a manometer or differential pressure gauge to measure pressure drop across the duct at a known airflow.
• B. Measure the duct temperature with a thermometer only.
• C. Use a voltmeter to assess electrical resistance in the duct.
• D. Count the number of turns to estimate resistance.

Answer: (A)