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Hydronic Heating Boilers and
Domestic Water Heaters
14
INSTALLATION
Continued
FIG. 15 Air Inlet Cap for Sidewall Termination
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 Service Manual.
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 (powered vent cap) if it is located within 10 feet
(3.05m) of the flue outlet from the powered vent cap. Make
sure to properly install the air inlet cap assembly on the air
inlet pipe.
You must install the combustion air inlet cap and the powered
vent cap on the same wall and in the same pressure zone.
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 24.
FIG. 16 Roof Top Combustion Air Inlet
Clearances
You must locate the air inlet termination elbow at least 12"
(30cm) above the roof or above normal snow levels.
12"
3'
TABLE–C
Minimum Recommended Combustion Air Supply To Boiler Room
Combustion Air Source
Boiler Input Outside Air*/2 Openings Outside Air*/1 Opening Inside Air/2 Openings
399,999 100 in
2
(745 cm
2
) 133 in
2
(858 cm
2
) 400 in
2
(2581 cm
2
)
500,000 125 in
2
(806 cm
2
) 167 in
2
(1077 cm
2
) 500 in
2
(3226 cm
2
)
650,000 163 in
2
(1052 cm
2
) 217 in
2
(1400 cm
2
) 650 in
2
(4194 cm
2
)
750,000 188 in
2
(1213 cm
2
) 250 in
2
(1613 cm
2
) 750 in
2
(4839 cm
2
)
990,000 248 in
2
(1,600cm
2
) 330 in
2
(2,129 cm
2
) 990 in
2
(6,388 cm
2
)
1,260,000 315 in
2
(2,032cm
2
) 420 in
2
(2,710 cm
2
) 1260 in
2
(8,130 cm
2
)
1,440,000 360 in
2
(2,323cm
2
) 480 in
2
(3,097 cm
2
) 1440 in
2
(9,291 cm
2
)
1,800,000 450 in
2
(2,903cm
2
) 600 in
2
(3,871 cm
2
) 1800 in
2
(11,614 cm
2
)
2,070,000 518 in
2
(3,342cm
2
) 690 in
2
(4,452 cm
2
) 2070 in
2
(13,356 cm
2
)
*Outside air openings shall directly communicate with the outdoors. When combustion air is drawn from the outside through a duct, the net free area of each of the two openings
must have twice (2 times) the free area required for Outside Air/2 Openings. The above requirements are for the boiler only, additional gas fired units in the boiler room will require
an increase in the net free area to supply adequate combustion air for all units. Combustion air requirements are based on the latest edition of the National Fuel Gas Code, ANSI
Z223.1, in Canada refer to CAN/CGA-B149 Installation Code. Check all local code requirements for combustion air.