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2.1.7
INLET CAP FOR ROOFTOP TERMINATION
The air inlet cap consists of two 90° elbows instal led at the
point of termination for the air inlet pipe. The first 90° elbow
is installed on the rooftop at the highest vertical point of the
air inlet pipe and turned horizontal; the second 90° elbow is
screened and is installed on the horizontal outlet of the first
elbow and turned down. A 90° elbow and a 90° street elbow
may be used to make this assembly. If a straight piece of
pipe is used between the two elbows, it should not exceed
6" (150mm) in length.
2.1.8
LOCATION OF A ROOFTOP AIR INLET AND
VENT CAPS
•
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) if it is located within a 5 foot
(1.5M) radius of the flue outlet. Use care to ensure that
the 90° elbow assembly is properly installed on the air
inlet pipe.
•
The termination point of the combustion air inlet cap
must be installed at least 3 feet (0.91M) above the
rooftop and above normal snow levels.
•
The vent cap assembly MUST be listed by nationally
recognized agencies.
•
The combustion air cap and vent cap MUST be located
on the same roof top surface and in the same pressure
zone
•
Combustion air supplied from outdoors must be free of
contaminants. To prevent recirculation of flue products
in to the combustion air inlet, follow all instructions in
this section.
•
Incorrect installation and/or location of the air inlet cap
can allow flue products to be drawn back into the
appliance. This can result in incomplete combustion
and potentially hazardous levels of carbon monoxide in
the flue products. This will cause operational problems
with the appliance and if left uncorrected, will lead to
conditions that can cause personal injury or death.
2.1.9
AIR INLET DAMPER
In warmer climates, during cold weather, the use of ducted
outdoor air may result in the formation of condensation on
the interior panels of the combustion chamber. It may be
possible for this condensation to accumulate and drip out of
the appliance jacket. If this is not acceptable, it is advisable
to install a motorized combustion air damper in the
combustion air duct interlocked with the appliance's start
circuit. In cold climates it is essential to provide a motorized
air inlet damper to control the supply of combustion air and
prevent nuisance condensation.
Figure 6: Air Inlet Damper Connection Inside J-Box
2.1.10
MASONARY CHIMNEY INSULATIONS
Always follow local codes when venting this appliance into
a masonry chimney. A standard masonry chimney must
NOT be used to vent the products of combustion from the
flue of a Condensing, positive or negative pressure
appliance (Category II or IV). If a masonry chimney is to be
used, the chimney MUST use a sealed, metallic, corrosion
resistant liner system to vent flue products from this high
efficiency appliance. Sealed, metallic, corrosion resistant
liner systems (AL29-4C or equivalent, single wall or double-
wall, or flexible or rigid metallic liners) must be rated for use
with a high efficiency condensing, positive pressure vent
system. Corrosion resistant chimney liner systems are
typically made from a high grade of corrosion resistant
stainless steel such as AL29-4C or equivalent. The
corrosion resistant liner must be properly sized and fully
sealed throughout the entire length. If the flue is contained
within the masonry chimney both the top and the bottom of
the masonry chimney must be capped and sealed to
provide a dead air space around the sealed corrosion
resistant metallic liner.
Consult with local code officials to determine code
requirements or the advisability of using a masonry
chimney with a sealed corrosion resistant liner system.
2.1.11
VERTICAL VENTING TERMINATION
•
Follow Category II or IV vent termination and all
General instructions.
•
The vent terminal should be vertical and exhaust
outside the building at least 2 feet (0.61M) above the
highest point of the roof within a 10 foot (3.05M) radius
of the termination.
•
The vertical termination must be a minimum of 3 feet
(0.91M) above the point of exit.
•
A vertical termination less than 10 feet (3.05M) from a
parapet wall must be a minimum of 2 feet (0.61M)
higher than the parapet wall.
2.1.12
COMBINED COMBUSTION AIR INLET
The air inlet pipes from multiple appliances 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.
Equivalent pipe diameter = Sq Root [(d
2
2
(d
)
+......+ (d
)
], d, pipe diameter
4
n
Example: What is equivalent pipe diameter of three air
inlet pipes, 8" (20.3 cm), 10" (25.4 cm) and 12" (30.5
cm)
Equivalent pipe diameter = Sq Root [(8)
Sq Root (308) = 17.5", Select 18" (82.8 cm) diameter pipe
or larger.
The air inlet point for multiple boiler 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 100" (30.5M) equivalent feet. You must deduct
the restriction in area provided by any screens, grills or
louvers installed in the common air inlet point. 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. Calculate and compensate accordingly for
the restriction.
2
2
2
)
+ (d
)
+ (d
)
+
1
2
3
2
2
2
+ (10)
+ (12)
] =
10
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