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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
Maintain a minimum 1" (25 mm) clearance to
combustibles on the vertical sections. Clear-
ances for the horizontal runs are; 3" (76 mm)
on top, 1" (25 mm) on sides, and 1" (25 mm)
at the bottom.
B. Frame exterior wall opening -
Locate the center of the vent outlet on
the exterior wall according to the dimen-
sions shown in Figure 11 on Page 10. Cut
and/or frame an opening, 10-1/2" x 12-1/8"
(267 mm x 308 mm) inside dimensions, about
this center.
C. Frame ceiling opening - If the vertical route
is to penetrate a ceiling, use plumb line to locate
the center above the appliance. Cut and/or frame
an opening, 10-1/2" x 10-1/2" (267 mm x 267
mm) inside dimensions, about this center (refer
to Figure 16 on Page 14).
VERTICAL VENT FIGURES/TABLES (CONTINUED)
HORIZONTAL (OUTSIDE WALL)
TERMINATION SYSTEM
Figure 26 on Page 18, and Figures 27 to 32
on Pages 19 through 22 and their associated
Horizontal Vent Table which illustrate the
various horizontal venting configurations that
are possible for use with these appliances.
Secure Vent™ pipe applications are shown in
these Figures; Secure Flex™ pipe may also
be used. A Horizontal Vent Table summarizes
each system’s minimum and maximum vertical
and horizontal length values that can be used
to design and install the vent components in a
variety of applications.
Both of these horizontal vent systems terminate
through an outside wall. Building Codes limit or
prohibit terminating in specific areas. Refer to
Figure 6 on Page 7 for location guidelines.
Secure Vent SV4.5 direct-vent system compo-
nents are unitized concentric pipe components
featuring positive twist lock connection, (refer
to Figure 17 on Page 14). All of the appli-
ances covered in this document are fitted with
collars having locking inclined channels. The
dimpled end of the vent components fit over
the appliance collar to create the positive twist
lock connection.
A. Plan the vent run -
Analyze the vent routing and determine the
types and quantities of sections required
4-1/2" (114 mm), 10-1/2" (267 mm), 22-1/2"
(572 mm), 34-1/2" (876 mm) and 46-1/2" (1181
mm) net section lengths are available. It is
recommended that you plan the vent lengths
so that a joint does not occur at the intersection
of ceiling or roof joists. Make allowances for
elbows as indicated in Figure 19 on Page 15.
LENNOXHEARTHPRODUCTS•MERIT
®
SERIESDIRECT-VENTCONTEMPORARYDESIGNGASFIREPLACES•MODELMLDVTCD-35•INSTALLATIONINSTRUCTIONS
u
Ceiling
Firestop / Spacer
(SV4.5VF)
v
Wall Firestop/
Spacer (SV4.5HF)
u When using Secure Flex, use Firestop / Spacer SF4.5VF
v When using Secure Flex, use Firestop / Spacer SF4.5HF
V
H
1
H
V
1
Example: If 20 feet total (H+H
1
)
horizontal vent run is needed, then
4 feet minimum of (V) vertical vent
will be required.
This table shows a 1(V) to 5(H)
ratio. For every 1 foot of (V)
vertical, you are allowed 5 feet
of (H+H
1
) horizontal run up to
a maximum total horizontal run
of 20 feet.
An elbow is acceptable as 1 foot
of vertical rise except where
an elbow is the only vertical
component in the system. See
Figure 29.
Table B
H +
H
1
Maximum
V Minimum
feet (meter) feet (meter)
5 (1.524) Elbow Only
5 (1.524) 1 (0.305)
10 (3.048) 2 (0.610)
15 (4.572) 3 (0.914)
20 (6.096) 4 (1.219)
H + H
1
= 20 feet (6.096 m) Max.
V + V
1
+ H + H
1
= 40 ft. (12.2 m) Max.
Figure 25 - Top Vent - THREE ELBOWS