Lennox VRF V22B Series Installation Instruction page 16

Supply Duct
NOTE - The secondary supply duct must be 4 or 6 inches in diameter and 10 feet or less
in length (including transitions).
Figure 18. Possible Air Flow Patterns
Supports
10 feet maximum
Seal supply air outlet on duct side
Figure 19. Supply Duct Maximum Length
16
Drop Ceiling