Installer’s Guide
15
Reduction of Clearances with Specified Forms of Protection
Type of Protection
Allowable Clearance with
Specified Protection (in.)
Applied to and covering all surfaces
of combustible material within the
distance specified as the required
clearance with no protection. See
Figure 11.
Where the required clearance
with no protection from the ap-
pliance or chimney connector
is:
9 inches
Above
Sides & Rear
a. 3 -1/2" thick masonry wall with-
out ventilation air space.....
---
6
b. 1/2" insulation board over 1"
glass fiber or mineral wool batts.....
6
5
c. 0.024 (24 gauge) sheet metal
over 1" glass fiber or mineral wool
batts reinforced with wire on rear
face with ventilated air space.....
5
3
d. 3 - 1/2" thick masonry wall with
ventilation air space.....
---
6
e. 0.024 (24 gauge) sheet metal
with ventilated air space.....
5
3
f. /2" insulation board with venti-
lated air space....
5
3
g. 0.024 (24 gauge) sheet metal
with ventilated air space over 0.024
(24 gauge) sheet metal with venti-
lated air space.....
5
3
h. 1" glass fiber or mineral wool
batts sandwiched between two
sheets 0.024 (24 gauge) sheet
metal with ventilated air space
5
3
A. Equal the required clearance with no protection.B. Equals the
reduced clearance permitted in accordance with the preceeding
clearance chart.C. The protection applied to the construction that
covers the combustible material should extend far enough in each
direction to make C equal to A.
The vent connector pipe between the furnace and
chimney shall be of equal diameter as the flue outlet of
the furnace.
The vent connector pipe must be made of 24
gauge (or thicker) corrosion-resistant steel.
The vent connector pipe should be as short as possible
and installed so that it has a continuous rise from the
furnace to the chimney. The horizontal length of a
connector to a natural draft chimney or vent serving
a single appliance shall not be more than 75 percent
of the height of the vertical portion of the chimney or
vent above the connector. Elbows should be minimized
and the pipe should be joined with metal screws
and supported by straps. All horizontal runs of vent
connector pipe should be pitched upward a minimum
of 1/4 inch per foot of run.
A thimble should be used to connect the vent connector
pipe to the chimney so the pipe may be readily removed
in case of inspection or replacement. See Fig. 10.
All chimney clean-out doors and flue connections must
fit tightly so they will seal to avoid air leaks.
If chimney flues are divided or there are multiple flues
within one chimney, make sure there are no openings
in the partition separating the divided or individual
flues.
The vent connector pipe must not pass through
a combustible wall or partition unless adequate
protection is provided at the passageway. An acceptable
passageway could be either an approved, ventilated
metal thimble which is at least 12 inches larger in
diameter than the vent connector pipe, or brick work
which is at least 8 inches thick constructed into the
wall and surrounding the vent connector pipe. (See
Fig. 10).
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