Where sufficient clearance for proper horizontal venting cannot be provided, or in jurisdictions requiring a 4 foot
separation between flue gas discharge and combustion air inlet, flue gases need to be vented vertically. Refer to Fig.
5 for acceptable venting method.
Vent pipe must terminate at least 1 ft. above the cabinet. The vent must be located on the same side of the appliance
as the combustion air inlet opening. Condensation in the vent pipe is likely during heater start-up cycle and provision
for drainage must be provided
Figure 5
Combustion Air Opening
ID
Fan
Rectangular to
Round adapter
Condensate
Drain
AHU
Cabinet
4 ft. Min.
12 in. Min
Field Starkap or equal
listed Vent cap
Venting Indoor Installations
All furnace modules must be connected to a venting system to convey flue gases outside of the heated
space.
Vertically Vented Duct Furnaces –Category I
Vent systems must be sized and installed in accordance with ANSI Z223.1 (NFPA 54), Chapters 7 and 10. Proper venting of the
heating units is the responsibility of the installer. When custom designed systems provided by vent system manufacturers are field
installed, proper heating unit operation must be verified, including flue gas analysis of each connected heater.
1. Use single wall or double wall (Type B) vent pipe of diameters listed in Table 1.
Table 1 Input Rating (Btuh) Input Rating (W) Vent Pipe Dia.
75,000 –149,999 21,980 –43,958 5 in. (126 mm)
150,000 –400,000 43,960 –117,228 6 in. (152 mm)
401,000 –600,000 117,229 –175,842 7 in. (178mm)
2. Maximize the height of the vertical run of vent pipe. A minimum of five (5) feet (1.5m) of vertical pipe is required. The top of
the vent pipe must extend at least two (2) feet (0.61m) above the highest point on the roof. (Use Listed Type B vent for
external runs).
3. An approved weatherproof vent cap must be installed to the vent termination.
4. Horizontal runs must not exceed 75% of the vertical height of the vent pipe, up to a maximum of ten (10) feet (3m).
Horizontal runs should be pitched upward ¼” per foot (21mm/m) and should be supported at 3 foot (1m) maximum intervals.
5. Design vent pipe runs to minimize the use of elbows. Each 90o elbow is equivalent to 5 feet (1.5m) of straight vent pipe run.
6. Vent pipe should not be run through unheated spaces. If such runs cannot be avoided, insulate vent pipe to prevent
condensation inside vent pipe. Insulation should be a minimum of ½” (12.7mm) thick, foil faced material suitable for
temperatures up to 500 oF.
Flue gases must be directed
away from combustion air
inlets, to avoid recirculation
into combustion air supply.
