In terms of interior ductity, what must not be deformed to more than 12-1/2 square inches?

The requirement that states an area cannot be deformed to more than 12-1/2 square inches is related to electric dryer vent connections. This specification ensures that the airflow is not significantly impeded, which is crucial for efficient and safe operation. When electric dryers are used, they produce a lot of lint and moisture, and if the vent connection is deformed too much, it can restrict airflow, leading to potential overheating or fire hazards. Maintaining the integrity of the vent connection is essential for ensuring that exhaust is effectively expelled, and that moisture and lint do not build up within the system.

In the context of other options: while the dimensions of dryer vents and the interior diameters of flexible ducts are important considerations for proper venting, they are not specifically associated with that maximum deformation threshold. Similarly, the outer casing of dryer vents mainly serves as a structural component and its deformation limits may vary depending on different factors beyond that specific square inch measurement. Hence, the focus on connection integrity directly links to the safety and functionality of dryer exhaust systems.