16
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
u Ceiling Firestop /
Spacer (SV4.5VF)
u When using
Secure Flex, use
Firestop/Spacer
SF4.5VF
A Vent Restrictor,
as shown in Figure
16 Page 12, must
be used in this
application
Figure 25 - Top Vent - STRAIGHT
u Ceiling Firestop /
Spacer (SV4.5VF)
vWall Firestop/
Spacer (SV4.5HF)
u When using Secure Flex, use Firestop /
Spacer SF4.5VF.
v When using Secure Flex, use Firestop /
Spacer SF4.5HF.
H
V
V1
Table A
H 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)
V + V1 + H = 60 feet (18.3 m) Max.
H = 20 feet (6.096 meters) Max.
60 feet
(18.3 meters)
Maximum
VERTICAL VENT FIGURES/TABLES
Notes:
• Secure Vent™ (rigid vent pipe) is shown
in the Figures; Secure Flex™ (flexible vent
pipe) may also be used.
• 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 accept-
able all the way down to at or near level.
• SV4.5VF (Secure Vent), SF4.5VF (Secure
Flex) restop/spacer must be used anytime
vent pipe passes through a combustible
oor or ceiling. SV4.5HF (Secure Vent),
SF4.5HF (Secure Flex) restop/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 31 on Page 20).
WARNING
Under no circumstances may sepa-rate sections of concentric flexible vent pipe be joined together.Figure 26 - Top Vent - TWO 90 DEGREE ELBOWS
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 31).
LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS