43
When vent pipe is run through unheated
spaces where temperatures may be below
freezing, pipe should be insulated using ½
inch
(22.7mm)
thick
Armaflex-type
insulation or heated with a thermostatically
controlled heat tape.
Gas furnaces feature high efficiency
operation and produce condensate during
operation. In locations where the outside air
temperature is below freezing, icicles may
form on vent terminations from the
condensate formed in the vent system.
Open Combustion Venting
An open combustion gas heater draws
combustion air from the space surrounding
the heating unit. Louvered combustion air
openings are provided in the access panel to
the burner vestibule area. Installation must be
in an unconfined space with sufficient
volume for all appliances located in the
space.
A single, properly sized pipe from the
furnace vent connector to the outdoors must
be provided.
Vent pipe diameter and maximum vent
length are determined by furnace input rating
as shown in Table 8. Flue gases must be
directed downward.
Table 8 - Open Combustion Venting
Model
Size
Input
(MBtu
/hr)
Maximum Vent Length
(ft)
2”
PVC
3”
PVC
4”
PVC
V3-A
45
90
100
100
60
60
100
100
V3-B
72
40
100
100
108
15
100
100
V3-C
80
30
100
100
120
10
90
100
160
N/A
50
100
Notes:
1.
Maximum
vent
length
is
the
equivalent linear length of the pipe
and fittings. See Table 9 for
equivalent lengths for fittings.
2.
DWV pipe and fittings should be used
instead of SCH 40 pressure pipe and
fittings to reduce overall vent
pressure drop.
3.
For separated combustion systems,
the maximum vent length is a
combination of the combustion air
intake and flue vent exhaust pipes.
For example a 60MBtu/hr heater
using 3”PVC can have a 50 ft
combustion air intake run and a 50 ft
flue vent exhaust run.
VENT TERMINATION
In locations where the outside
temperature falls below freezing,
icicles may form on vent terminations
due to condensate in the vent system.
Locate vent termination where a
falling icicle would not be a hazard.
WARNING
VENT TERMINATION
Vent terminals must be positioned and
located away from fresh air intakes,
doors, and windows to minimize the
possibility of products of combustion
from entering occupied space.
WARNING
