Start with the required ventilation airflow, then evaluate the unit's delivered airflow at the planned external static pressure, recovery performance, filtration, sound levels, dimensions, power consumption, controls, and maintenance access.

The appropriate capacity depends on occupancy, building layout, local ventilation requirements, duct design, and operating conditions. A unit's maximum airflow alone is not enough to determine suitability.

For larger homes and villas, room-by-room airflow distribution and the available installation space should also be considered.