How can you verify that return air from one zone is not undesirably entering another zone?

• A. Monitor room pressures, use doors/pressure differentials, perform smoke visualization, and verify that return paths do not cause crossflow.
• B. Seal all doors and never open them during testing.
• C. Return air crossflow is acceptable as long as zones meet CFM targets.
• D. Only measure differential pressure between the supply and return plenums.

Answer: (A)