Empire Comfort Systems DVLXG75BP90N-1 Installer's Manual page 28

Vertical Firestops
Vertical runs of this system which pass through ceilings require
the use of ONE ceiling firestop at the hole in each ceiling through
which the vent passes.
Position a plumb bob directly over the center of the vertical vent
component and mark the ceiling to establish the center point
of the vent. Drill a hole or drive a nail through this center point
and check the floor above for any obstructions such as wiring
or plumbing runs. Reposition the fireplace and vent system, if
necessary, to accommodate ceiling joists and/or obstructions.
Cut a 10-5/8 inch x 10-5/8 inch hole through the ceiling, using
the center point previously marked. Frame the hole with framing
lumber the same size as the ceiling joists. If the area above the
ceiling is NOT an attic, position and secure the ceiling firestop on
the ceiling side of the previously cut and framed hole.
If the area above the ceiling is an attic, position and secure the
firestop on top of the previously framed hole.
NOTICE: Remove insulation from the framed area in the attic
before installing the firestop and/or vent pipes.
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VENT FRAMING AND FINISHING
When finishing the fireplace never obstruct or modify the air
inlet/outlet louvers in any manner. Provide adequate clearances
around air openings into the combustion chamber.
WARNING