How can exhaust fans that operate on a set schedule create issues during testing?

Exhaust fans that operate on a set schedule can create significant issues during airtightness testing because they may remain operational when they should be off. During a whole-building airtightness test, all mechanical equipment, including exhaust fans, should ideally be turned off to obtain an accurate measurement of the building's air leakage. If these fans continue to run, they can create additional air movement that will introduce uncontrolled airflow into the building, leading to inflated test results. This can result in an underestimation of the building's airtightness, which would not accurately reflect its performance in real-world conditions.

By ensuring that exhaust fans are fully disengaged during the testing process, you maintain the integrity of the test results, allowing for a valid assessment of the building's air tightness. Other concerns, such as noise, calibration, or power connections, are secondary compared to the fundamental issue of ensuring that all systems that could impact air pressure and flow are properly accounted for or taken out of operation.