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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
Figure 44: Top Vent - THREE 90-DEGREE ELBOWS
Figure 43: Rear Vent - THREE 90-DEGREE ELBOWS
See Table 8 on page 21 as an aid in venting component selection for a particular range of exterior wall thicknesses.
See Table 8 on page 21 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.
HORIZONTAL VENT FIGURES/TABLES (continued)
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.
An elbow is acceptable as 1 foot of vertical
rise except where an elbow is the only verti-
cal component in the system. See Figure 39.
V Minimum
feet
feet
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)
(meters)
TABLE L
(meters)
H Maximum
1 1
H
+ H
1
= 20 feet (6.096 m) Max.
V
+ V +
H
+ H = 40 ft. (12.192 m) Max.
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.
V
H
H
1
V
1
Ceiling
Firestop/Spacer
SV4.5VF*
*When using Secure Flex, use
Ceiling Firestop/Spacer SF4.5VF.
**When using Secure Flex, use
Wall Firestop/Spacer SF4.5HF.
Wall Firestop/Spacer
SV4.5HF**
Wall Firestop/Spacer
SV4.5HF**
V
H
2
H
1
H
Ceiling
Firestop/Spacer
SV4.5VF*
*When using Secure Flex, use
Ceiling Firestop/Spacer SF4.5VF.
**When using Secure Flex, use
Wall Firestop/Spacer SF4.5HF.
Wall Firestop/Spacer
SV4.5HF**
H Maximum
V Minimum
feet feet feet
5 (1.524) 2 (0.610) 1 (0.305)
10 (3.048) 4 (1.219) 2 (0.610)
15
(4.572)
6 (1.829) 3 (0.914)
20 (6.096) 8 (2.438) 4 (1.219)
V + H + H
1
+ H
2
= 40 feet (12.2 m) Max.
H = 8 feet (2.438 meters) Max.
H + H
1
+ H
2
= 20 feet (6.096 meters) Max.
H
+ H
1
+ H
2
Maximum
TABLE K
(meters)
(meters)
(meters)