NEC NP4100WJ User Manual page 12

Important Information
(3) Upward or downward projection:
When using the projector in an upward projection angle, allow 1 m/ 40 inches or
greater between the exhaust vent and the wall.
When using the projector in a downward projection angle, allow 0.5 m/ 20 inches or
greater between the exhaust vent and the wall.
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