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PROTECTION REQUIRED FOR CLEARANCES LESS
THAN 6 INCHES FROM DOUBLEWALL VENT PIPE*
DIMENSION A
When desired minimum
clearance from type “L”
doublewall vent pipe to Use the following
combustible surface is: protection**:
½" thick insulation board ***
3" over one-inch glass fiber or
mineral wool batts+
24 gauge sheet metal with
2" one-inch ventilated air space
½" thick insulation board ***
3" with one-inch ventilated air space
Appendix
CONTINUED
* All clearances measured from outer surface of equipment to combustible
surface, not to the protection used.
** Apply to combustible surface unless otherwise noted. Cover all surfaces as
specified in Table and FIGURE 19. Thicknesses are minimum.
*** Factory-fabricated board made of non-combustible materials, normally fibers,
having thermal conductivity in range of one (Btu-inch)/(hr./sq. ft./°F) or less.
+ Mineral wool batts (blanket or board), having min. density of 8 lb/ft
3
and a min.
melting point of 1500°F.
OTHER DIMENSIONS AVAILABLE. REFER TO NFPA-31.
Flue Pipe Clearances
FIGURE 19
Back Vent Clearances
FIGURE 20
Top Vent Clearances
FIGURE 21
24" For Servicing
or Min. 2" for Close
Clearances
Combustible
Surface
Combustible
Surface
Combustible
Surface
Combustible
Surface
A
A
A
A
2"
NOTE: 2" Min. on Sides
NOTE: 2" Min. on Sides
24" For Servicing
or Min. 2" for Close
Clearances
2"
2"
Combustible Surface
Protection
Type “L” Doublewall
Vent Piping
6"
A
6"
27