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2
Venting
2. For PVC, CPVC, ABS, dryer vent, or flex duct air inlet piping, use a silicone sealant to ensure a proper seal at the unit inlet and
the air inlet cap.
3. For Dryer vent or flex duct, also use a screw-type clamp to attach the inlet vent material to the unit inlet and the air inlet cap.
Properly sealing the air inlet pipe ensures that combustion air will be free of contaminates and supplied in proper volume.
4. Ensure that the air inlet pipes are properly supported.
Properly seal all joints and seams in the inlet vent piping system. Failure to do so may result in flue gas
WARNING
recirculation, spillage of flue products, and carbon monoxide emissions. Carbon monoxide poisoning can
cause severe personal injury or death.
Vertical and sidewall combustion air inlet
To prevent recirculation of flue products into the combustion air inlet, follow all instructions in this section.
NOTICE
Locate and install the combustion air inlet termination correctly. Failure to do so can allow the discharge
WARNING
of flue products to be drawn into the combustion process. This can result in incomplete combustion and
potentially hazardous levels of carbon monoxide in the flue products. This will cause operational problems
and the spillage of flue products. Spillage of flue products can cause personal injury or death due to carbon
monoxide poisoning.
You must locate the combustion air cap and the flue gas outlet on the same rooftop surface (vertical direct vent system) or sidewall
surface (horizontal direct vent system) and in the same pressure zone as the vent termination. Follow all clearance requirements
listed on this page.
Purchase and assemble the combustion air inlet cap to protect the air inlet from wind and weather.
Alternatively, assemble the combustion air inlet cap for vertical rooftop air inlet from items purchased locally. The air inlet cap
consists of two 90° elbows installed to the air inlet pipe (see FIG. 2-12). Install the first 90° elbow on the rooftop at the highest
vertical point of the air inlet pipe. Install the second 90° elbow on the horizontal outlet of the first elbow. The outlet of the second
90° elbow will be pointing down. You may use a 90° elbow and a 90° straight elbow to make this assembly. If you use a straight
piece of pipe between the two 90° elbows, it should not exceed 6" (51mm) in length.
Figure 2-12_Vertical Rooftop Air Inlet
Horizontal combustion air inlet clearances
You must locate the horizontal air inlet termination point at least 12" (30cm) above grade and 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 horizontal combustion air
inlet cap above the flue outlet.
Do not install the combustion air inlet cap closer than 10 feet (3.05m) from an inside corner of an L-shaped structure.
Multiple sidewall direct vent installations
You must locate the horizontal air inlet termination points at least 12" (30cm) above grade and above normal snow levels. The
combustion air inlet caps for multiple appliance installations must maintain the same minimum clearance from the closest flue vent
cap as specified in single appliance installations. You may install multiple flue outlet caps side-by-side and multiple combustion
air inlet caps side-by-side, but the air inlet must always be at least 3 feet (0.91m) horizontally and 3 feet (0.91m) below the closest
flue outlet. Do not install combustion air inlet caps above the flue outlets.
Maintain all clearances and installation requirements for multiple appliance installations.
30
6"
MAX
Installation & Operation Manual
For horizontal direct vent termination of combustion air, you
must use the termination cap from the appliance manufacturer.
The sidewall air inlet cap is available as part of a direct vent kit.
See Table 2E, page 28 for Horizontal Direct Vent Kits.
Vertical Combustion Air Inlet Clearances
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.
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