Mastic Spark Modern Fires 91P - Manual (Page 24)

24 L100001 25
VENT INSTALLATION
4. Connect a section of pipe and extend up through the hole.
NOTE: If an offset is needed to avoid obstructions, you must support the vent pipe every three (3) feet. Use wall
straps for this purpose. See Figure 25, page 22. Whenever possible, use 45° elbows instead of 90° elbows. The 45°
elbow offers less restriction to the flow of the flue gases and intake air.
5. Place the flashing over the pipe section(s) extending through the roof. Secure the base of the flashing to the roof and framing
with roofing nails. Be sure roofing material overlaps the top edge of the flashing. There must be a 1" clearance from the vent
pipe to combustible materials.
6. Continue to add pipe sections until the height of the vent cap meets the minimum building code requirements.
NOTE: You must increase vent height for steep roof pitches. Nearby trees, adjoining roof lines, steep pitched roofs,
and other similar factors may cause poor draft or down-drafting in high winds. Increasing the vent height may solve
this problem.
NOTE: If the vent pipe passes through any occupied areas above the first floor, including storage spaces and closets,
you must enclose pipe. You may frame and sheetrock the enclosure with standard construction material. Make sure
to meet the minimum allowable clearances to combustibles. Do not fill any of the required clearance spaces with
insulation.
Figure 30 - Cathedral Ceiling Support Box Installation
Figure 31 - Installed Cathedral Ceiling
Support Box
CATHEDRAL CEILING INSTALLATION
IMPORTANT: Review all information on previous page
before planning this installation. Cathedral ceiling
installations can be very tricky.
1. Remove shingles or other roof covering as necessary to cut
the rectangular hole for the support box. Mark the outline
of the cathedral ceiling support box on the roof sheathing
using the locating hole as a center point.
2. Cut the hole 1 /
8
" larger than the support box outline. See
Figure 30.
3. Lower the support box through the hole in the roof until
the bottom of the box extends at least 2" ( 51 mm ) below the
ceiling. See Figure 30. Align the support box vertically and
horizontally using a level. Temporarily tack the support box
in place through the inside walls and into the roof sheet-
ing.
4. Using tin snips, cut the support box from the top corners
down to the roofline and fold the resulting flaps over the
roof sheeting. See Figure 31. Apply a bead of non-hardening
mastic around the top edges of the support box to make a
seal between the box and the roof. Nail in place with roof-
ing nails. Remove any combustible material that might be
inside the support box.
5. Complete the cathedral ceiling installation by following
the same procedure outline d in steps 2 through 6 for Flat
Ceiling Installation, page 23 and above.
Level
Cathedral
Ceiling Support
Box
2" Minimum
Below
Finished
Ceiling
Cut Hole 1/8" Larger
than Support Box
when Projected onto
Roofline.
Apply Non-hardening
Mastic Under all Edges of
Support Box before Nailing