A server room with a false ceiling and subfloor is tested for integrity using a door fan test. What can be assumed from the test results?

• A. 60% beneath the false ceiling
• B. 25% above the ceiling
• C. 75% above the false ceiling
• D. 50% above the false ceiling

Answer: (D)

The door fan test measures how much air leaks from a space to maintain a set pressure difference. In a room that has both a false ceiling (creating a plenum above) and a subfloor (creating a plenum below), air can leak into either plenum. If the two leakage paths are similar in size and resistance, the leakage will distribute roughly equally between them. So, from the test results you can assume that about half of the leakage goes into the space above the false ceiling, and half goes into the space below. The other percentages would imply a bias in one direction, which isn’t indicated by a symmetric setup like this.