SECTION
8
: V
ENTING
35
8
.2 Unvented Operation
Sufficient ventilation must be provided in the amount
of 4 cfm per 1000 Btu/h firing rate (United States); 3
cfm per 1000 Btu/h firing rate (Canada).
Use of optional outside combustion air is not
recommended with unvented heaters.
If exhaust fans are used to supply ventilation air, an
interlock switch must be used to prevent the heater
from coming on when the fans are off. This may be
done using a pressure switch.
8
.3 Horizontal Ventin
g
In noncombustible walls only, vent terminal
(P/N 02537801-1P) may be used.
For 4" (10 cm) vents in either combustible or
noncombustible walls, use Tjernlund VH1-4 (P/N
90502100) or equivalent, insulated vent terminal.
Follow the manufacturer's instructions for proper
installation.
For 6" (15 cm) common vents in either combustible
or noncombustible walls, use Tjernlund VH1-6 (P/N
90502101) or equivalent, insulated vent terminal.
Follow the manufacturer's instructions for proper
installation.
8
.4 Vertical Ventin
g
For 4'' (10 cm) common vent, an approved vent cap
(P/N 90502300) must be used.
For 6'' (15 cm) common vent, an approved vent cap
(P/N 90502302) must be used.
For common vertical venting of more than two
heaters,
See Page 38, Section 8.10
.
A vent shall not extend less than 2' (0.6m) above the
highest point where it passes through a flat roof of a
building.
8
.5 Unvented Operation Tube Termination
Turndown type vent terminal with a screen must be
installed at the exhaust end of the tube. Vent terminal
design shall not incorporate backdraft flap.
FIGURE 22: Tube Termination
8
.6 Len
g
th Re
q
uirements
The maximum vent length allowed is 45' (13.7 m).
The maximum outside air supply duct length allowed
is 45' (13.7 m).
The total vent length, plus outside air duct length,
plus any extensions to minimum heat exchanger
lengths, cannot exceed 65' (19.8 m).
Vent length should be limited to less than 20' (6 m). If
using vent lengths greater than 20' (6 m),
condensation will form in the vent pipe. Insulation
and additional sealing measures (high temperature
silicone at all seams) are required. Optional heat
exchanger beyond minimum lengths is considered as
vent length for length determination.
Subtract 15' (4.6 m) of maximum allowed vent or duct
length per vent elbow if more than two are used.
WARNING
Combustion by-products contain a chemical
known to the State of California to cause
cancer and birth defects or other
reproductive harm.
