Vermont Castings • Defiant Flexburn 1975 Installation Manual_R1 • 2021 - ___ • 08/21
15
8390-035i
Thimble
Site constructed for masonry chimney installation:
Components
•
A minimum length of 305mm (longer for thicker walls) of
solid insulated factory-built chimney length constructed
to UL 103 Type HT 152mm inside diameter. Chimney
needs to extend a minimum of 51mm from the interior
wall and a minimum of 25mm from the exterior wall.
•
Wall spacer, trim collar and wall band to fit solid pack
chimney selected.
•
Minimum 203mm diameter clay liner section (if not
already present in chimney) and refractory mortar.
•
When jurisdiction requires install approved chimney liner
in masonry chimney.
Air Clearances
• Masonry chimney clearance must meet NFPA 211
minimum requirement of 51mm to sheet metal supports
and combustibles.
• Minimum of 25mm clearance around the chimney
connector.
• Top of wall opening is a minimum of 343 mm from
ceiling or 114mm below minimum clearance specified by
chimney connector manufacturer. NFPA 211 minimum
vertical clearance of 457mm from chimney connector
and ceiling or minimum recommended by chimney
connector manufacturer, Figure 4.3
Instructions
1. Open inside wall at proper height for the chimney
connector to enter the masonry chimney, Figure 4.3
2. Entry hole to masonry chimney must be lined with an
203mm minimum diameter clay liner, or equivalent,
secured with refractory mortar.
3. Construct a 432mm x 432mm outside dimension frame
from 2 x 2 framing lumber to fit into wall opening.
Inside opening of frame should be no less than 356mm
x 356mm, Figure 4.4. Attach the wall spacer to the
chimney side of the frame.
5. Nail the frame into the wall opening. The spacer should
be on the chimney side.
6. Insert the section of the solid insulated chimney into the
outer wall of the masonry chimney.
7. Tightly secure the length of the solid insulated chimney
with the wall band to the masonry chimney.
8. Insert a section of chimney connector into the chimney.
Make sure it does not protrude past the edge of the clay
chimney liner inside the chimney.
9. Seal the end of the chimney connector to the clay liner
with refractory mortar.
10. Install trim collar around the sold pack chimney section.
Figure 4.3
38mm
25mm
51mm
51mm
38mm
356mm ID
432mm OD
ceiling
Minimum 457mm
NFPA 211
343mm below ceiling to top
of opening
25mm
203mm
381mm 2x2 framing stud
51mm min air clearance
25mm min air clearance
114mm
or top of opening is a min.of
114mm below min.clearance
specified by connector mfg.
Center of Hole
Thimble
CL
CL
Wall
Include depth
of hearth pad
Solid Pack Chimney with Metal Supports as a Thimble
Trim Collar
Chimney Section
with 51mm
Clearance to
Combustibles
Chimney
Connector
Fire Clay Flue Liner
with Airspace
Masonry
Chimney
Wall Band to
Secure Chimney
Section
Wood Studs Used for
Framing - Spaced 51mm
clearance from Masonry
Chimney
Wall Spacer
Figure 4.4
35 mm Air Space to
Chimney Section
Min. Clearance
51 mm
Min. Chimney Clearance to Wall Spacer
and Combustible - 51 mm
Chimney
Flue Liner
Fireclay Liner
or Equivalent
Masonry Chimney
Constructed to NFPA 211
Wall Spacer
Wall Band
Trim Collar
Chimney Section
Chimney
Connector
Figure 4.5
