WARNING 5. When cutting or drilling into wall, or ceiling, do not damage electrical wiring or other hidden utilities. 6. Ducted fans must always be vented to the outdoors. 7. To reduce risk of fire, use only metal ductwork. 8. This unit must be grounded. CAUTION 1. For general ventilating use only. Do not use to exhaust hazardous or explosive material and vapors. 2. To avoid motor bearing damage and noisy and/or unbalanced impellers, keep drywall spray, construction dust, etc. off power unit. 3.