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speed. Do not operate summer exhaust fan. Close
fireplace dampers.
4. Place in operation the appliances being inspected.
Follow the manufacturer’s instructions for lighting
each appliance. Adjust thermostat so appliance
will operate continuously.
5. Check the pressure at a pressure tap located 12
in. above the bottom joint of the first vertical vent
pipe. Pressure should be anywhere between -0.01
and -0.08 in. WC.
6. After it has been determined that each appliance
remaining connected to the common venting sys-
tem properly vents when tested as outlined above,
return doors, windows, exhaust fans, fireplace
dampers and other gas burning appliances to their
previous conditions of use.
7. Any improper operation of the common venting
system should be corrected so that the installation
conforms with the NFGC (U.S.) or B149 (Canada).
When re-sizing any portion of the common venting
system, the common venting system should be re-
sized to approach the minimum size as
determined using the appropriate tables in the
NFGC (U.S.) or B149 (Canada).
*
Fig. 26: Horizontal Through-the-Wall Venting (Category III)
*Requires optional vent tee.
The total length of the horizontal through-the-wall flue
system should not exceed 70 equivalent ft in length. If
horizontal run exceeds 70 equivalent ft, an appropri-
ately sized extractor must be used. Each elbow used
is equal to 10 ft of straight pipe. This will allow installa-
tion in one of the four following arrangements:
• 70’ of straight flue pipe
• 60’ of straight flue pipe and one elbow
• 50’ of straight flue pipe and two elbows
• 40’ of straight pipe and three elbows
The vent cap is not considered in the overall length of
the venting system.
Horizontal Through-the-Wall Venting
(Category III)
Installation
These installations utilize the heater-mounted blower
to vent the combustion products to the outdoors.
Combustion air is taken from inside the room and the
vent is installed horizontally through the wall to the out-
doors. Adequate combustion and ventilation air must
be supplied to the equipment room in accordance with
the NFGC (U.S.) or B149 (Canada).
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