20
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
See Table 8 as an aid in venting component selection for a particular
range of exterior wall thicknesses.
See Table 8 as an aid in venting component selection
for a particular range of exterior wall thicknesses.
H

u

Wall
Firestop/Spacer
(SV4.5HF)
V

u

Whenusing Secure Flex,
use Firestop/Spacer
SF4.5HF
HORIZONTAL VENT FIGURES/TABLES
Notes:
• Secure Vent™ components (rigid vent pipe and terminal) are shown
in the Figures; Secure Flex™ components (flexible vent pipe and
terminal) may also be used.
• Two 45 degree elbows may be used in place of one 90 degree elbow.
The same rise to run ratios, as shown in the venting Figures for 90
elbows, must be followed if 45 degree elbows are used.
• SV4.5VF (Secure Vent), SF4.5VF (Secure Flex) restop/spacer must be
used anytime vent pipe passes through a combustible floor or ceiling.
SV4.5HF (Secure Vent), SF4.5HF (Secure Flex) restop/spacer must
be used anytime vent pipe passes through a combustible wall.
• It is very important that the horizontal/inclined run be maintained in
a straight line (no dips) and recommended to be in a slightly elevated
plane, in a direction away from the replace of 1/4" rise per foot (20
mm per meter) which is ideal, though rise per foot run ratios that are
smaller are acceptable all the way down to at or near level.
• The tables show a 1(V) to 5(H) ratio up to a maximum horizontal run
of 20 feet except for installations where an elbow is the only vertical
vent section in the system (see Figure 31).
• AN ELBOW IS ACCEPTABLE AS 1 FOOT OF VERTICAL RISE EXCEPT
WHERE AN ELBOW IS THE ONLY VERTICAL COMPONENT IN THE
SYSTEM (see Figure 31).
Use Table 8 as an aid in venting component selection for a particular
range of exterior wall thicknesses.
Figure 32 - Top Vent - ONE 90 DEGREE ELBOW -
ELBOW CONNECTION NOT DIRECTLY AT APPLIANCE
Figure 31 - Top Vent -
ONE 90 DEGREE ELBOW - ELBOW CONNECTION AT APPLIANCE
H
V
Wall Firestop/Spacer
(SV4.5HF)
Whenusing SecureFlex,
use Firestop/Spacer
SF4.5VF.
Ceiling
Firestop/Spacer
(SV4.5VF)
Whenusing SecureFlex,
use Firestop/Spacer
SF4.5HF.
Typical termination shown.
Typical termination shown.
Venting Components Required for Various Exterior Wall Thick-
nesses, when using Typical Termination Kits
Vent Components Required Exterior Wall Thickness - inches (mm)
Termination Kit Only 6 to 9-1/4 (152 to 235)
Termination Kit and 6 In. Vent
Section (SV4.5L6) 10-3/4 to 14 (273 to 356)
Termination Kit and 12 in.
Vent Section (SV4.5L12) 16-3/4 to 20 (426 to 508)
Termination Kit and Tele-
scopic Section (SV4.5L12) 11-3/4 to 20 (299 to 508)
Table 8 Note: See Figure 30 showing wall thickness range
when using SV4.5HT-2 termination kit.
Example: If 20 feet of (H)
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
vertical, you are allowed 5 feet
of (H) horizontal run up to a
maximum (H) horizontal run
of 20 feet.
WARNING

Under no circumstances, may separate sections of

concentric flexible vent pipe be joined together.

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS
Table C
H Maximum V Minimum
feet (meter) feet (meter)
3 (0.914) Elbow Only (30/35/40 Models)
2.5 (0.762) Elbow Only (45 Model)
Table D
H Maximum V Minimum
feet (meter) feet (meter)
5 (1.524) 1 (0.305)
10 (3.048) 2 (0.610)
15 (4.572) 3 (0.914)
20 (6.096) 4 (1.219)
V + H = 60 feet (18.3 m) Max.
H = 20 ft. (6.096 m) Max.