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2
Venting
(continued)
To prevent recirculation of flue products from an adjacent vent cap into the combustion air inlet, follow all applicable clearance
requirements in the latest edition of the National Fuel Gas Code and/or CAN/CGA-B149 Installation Code and instructions in the
Installation and Operation Manual.
Clearances
You must install the combustion air inlet cap at least one foot (0.30m) above ground level and above normal snow levels.
The point of termination for the combustion air inlet cap must be at least 3 feet (0.91m) below the point of flue gas termination if
it is located within 10 feet (3.05m) of the flue outlet. Make sure to properly install the air inlet cap assembly on the air inlet pipe.
Do not install the combustion air inlet cap closer than 10 feet (3.05m) from an inside corner of an L-shaped structure.
Vertical Rooftop Air Inlet
Use the vertical air inlet terminations available from the appliance manufacturer, recommended and/or supplied by the vent
manufacturer, or use two 90° elbows as described on page 30.
3'
MIN
12"
MIN
Figure 2-7_Rooftop Combustion Air Inlet
The air inlet point for multiple unit air inlets must be provided with an exterior opening which has a free area equal to or greater
than the total area of all air inlet pipes connected to the common air inlet. This exterior opening for combustion air must connect
directly to the outdoors. The total length of the combined air inlet pipe must not exceed a maximum of 50 (15.2m) equivalent feet.
Subtract 5 feet (1.5m) for each 90° elbow in the air inlet pipe. You must deduct the restriction in area provided by any screens, grills
or louvers installed in the common air inlet point. These are common on the sidewall air inlet openings. Screens, grills or louvers
installed in the common air inlet can reduce the free area of the opening from 25% to 75% based on the materials used.
You can terminate the combustion air pipe either horizontally with a sidewall air inlet or vertically with a rooftop air inlet. The
installed length of air inlet pipe from the unit to the outside air inlet cap must not exceed 50 equivalent feet (15.2m).
You must locate the air inlet termination elbow at least 12"
(30cm) above the roof or above normal snow levels.
If the air inlet cap is within a 10-foot (3.05m) radius of the flue
outlet, the point of termination for the combustion air inlet
cap must be at least 3 feet (0.91m) below the point of flue gas
termination (vent cap).
Do not install the combustion air inlet cap closer than 10 feet
(3.05m) from an inside corner of an L-shaped structure.
Combined air inlet points
The air inlet pipes from multiple units can be combined to a
single common connection if the common air inlet pipe has a
cross sectional area equal to or larger than the total area of all air
inlet pipes connected to the common air inlet pipe.
Example: Two 10" air inlet pipes (78.5 in
IMG00586
area of 157 in
2
and will require a 15" (176.7 in
air inlet pipe.
Installation & Operation Manual
area each) have a total
2
2
area) common
21
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