Lennox MLDVT-30NM Installation Instructions Manual page 15

Notes:
• 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.
• 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.
• 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.
• 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).
(8.3 meters)
u
Ceiling Firestop /
Spacer (SV4.5VF)
u
When using Secure Flex, use Firestop / Spacer
SF4.5VF
A Vent Restrictor, as shown in Figure 14
Page 11, must be used in this application
Figure 23
- Top Vent - STRAIGHT
60 feet
Maximum
V
u
W hen using Secure Flex, use Firestop /
Spacer SF4.5VF.
v
W hen using Secure Flex, use Firestop /
Spacer SF4.5HF.
Figure 24
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
H
u
Ceiling Firestop /
Spacer (SV4.5VF)
v
Wall Firestop/
Spacer (SV4.5HF)
- Top Vent - TWO 90 DEGREE ELBOWS
Table A
H Maximum
feet (meter) feet
5 (.524)
5 (.524)
0 (3.048)
5 (4.572)
20 (6.096)
V + V + H = 60 feet (8.3 m) Max.

H = 20 feet (6.096 meters) Max.
V
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 vertical
component in the system. See Figure 29.
V Minimum
(meter)
Elbow Only
 (0.305)
2 (0.60)
3 (0.94)
4 (.29)
5