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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT
®
PLUS DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
H Maximum
V Minimum
feet feet
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 = 40 feet (12.2 m) Max.
H = 20 ft. (6.096 m) Max.
TABLE G
(meters)
(meters)
TABLE F
H Maximum V Minimum
feet
feet
3
(0.914)
Elbow Only
(meters)
(meters)
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
(V) vertical, you are allowed
5 feet of (H) horizontal run,
up to a maximum horizontal
run of 20 feet.
Figure 39: Top Vent - ONE 90-DEGREE ELBOW -
ELBOW CONNECTION AT APPLIANCE
Figure 40: Top Vent - ONE 90-DEGREE ELBOW -
ELBOW CONNECTION NOT DIRECTLY AT APPLIANCE
See Table 3 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.
Square termination (SV4.5HT-2) shown.
Square termination (SV4.5HT-2) 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 37 showing wall thickness range
when using SV4.5HT-2 termination kit.
Only the square termination (SV4.5HT-2) may be used.
HORIZONTAL VENT FIGURES/TABLES
Note: 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.
Note: It is very important that the horizontal/inclined run be maintained
in a straight (no dips) and recommended to be in a slightly elevated
plane, in a direction away from the fireplace 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.
See Table 8 as an aid in venting component selection
for a particular range of exterior wall thicknesses.
Note: SV4.5VF (Secure Vent), SF4.5VF (Secure Flex) firestop/spacer must
be used anytime vent pipe passes through a combustible floor or ceiling.
SV4.5HF (Secure Vent), SF4.5HF (Secure Flex) firestop/spacer must be
used anytime vent pipe passes through a combustible wall.
Note: 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.
Figure 38: Rear Vent - NO ELBOWS
WARNING
Under no circumstances, may separate sections of
concentric flexible vent pipe be joined together.
H
H = 28 in. (711 mm) Maximum.
7 in
(178 mm)
Wall Firestop/
Spacer
SV4.5HF**
**When using Secure Flex, use
Wall Firestop/Spacer SF4.5HF.
H
V
Ceiling
Firestop/
Spacer
SV4.5VF*
Wall Firestop/
Spacer SV4.5HF**
*When using Secure Flex, use
Ceiling Firestop/Spacer SF4.5VF.
**When using Secure Flex, use
Wall Firestop/Spacer SF4.5HF.
H
V
Wall Firestop/
Spacer
SV4.5HF**
**When using Secure
Flex, use Wall Firestop/
Spacer SF4.5HF.