Combustion Air & Ventilation; All Air From Inside The Building; All Air From Outside The Building; Required Cross Sectional Duct Area - Smith Cast Iron Boilers GB300 Installation & Operating Manual

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GB300 BOILER INSTALLATION AND OPERATION INSTRUCTIONS
COMBUSTION AIR & VENTILATION
WARNING: This boiler must be supplied with
combustion air in accordance with Section 5.3,
Air for Combustion & Ventilation, of the latest
revision of the National Fuel Gas Code, ANSI
Z223.1/NFPA 54 and all applicable local building
codes. Canadian installations must comply with
CAN/CGA B149.1 or .2 Installation Code. Failure
to provide adequate combustion air for this boiler
can result in excessive levels of carbon
monoxide which can result in severe personal
injury or death!
WARNING: Never operate a GB300 in an
environment subjected to a negative pressure
unless it is Direct Vented. Failure to comply with
this warning can result in excessive levels of
carbon monoxide causing severe personal injury
or death!
To operate properly and safely this boiler requires a
continuous supply of air for combustion. Oxygen is used
by the boiler burners to burn the gas. NEVER store
objects on or around the boiler. In addition, air is also
used to assist in the safe disposal of the products of
combustion. This air is known as dilution air and mixes
with the products of combustion to assist in their exit
through the flue pipe and chimney. An adequate supply
of air must be available to replace the air used by these
processes.
Older buildings often have enough natural infiltration to
provide an adequate amount of combustion air provided
that the demand for combustion air is not too great.
Buildings that are relatively new or "tight" will most likely
require the installation of a fresh air duct or other means
of providing make-up air. Any building utilizing other gas
burning appliances, a fireplace, wood stove or any type
of exhaust fan must be checked for adequate combustion
air when all of these devices are in operation at one time.
Sizing of an outside air duct must be done to meet the
requirements of all such devices.

All Air From Inside The Building

If the boiler is to be located in a confined space
minimum clearances of 2 ft, 0.61 m must be maintained
between the boiler and any adjacent construction. When
installed in a confined space two permanent openings
communicating with an additional room(s) are required.
The combined volume of these spaces must have
sufficient volume to meet the criteria for an unconfined
space. The total air requirements of all gas utilization
equipment, fireplaces, wood stoves or any type of
exhaust fan must be considered when making this
determination.
Each opening must have a minimum free area of
2 /1000 Btu/hr, 2200 mm2/kW based on the total
1 in
input rating of ALL gas utilization equipment in the
confined area. Each opening must be no less than
2
100 in 2 , 64,516 mm in size. The upper opening must be
within 12 in, 300 mm of, but not less than 3 in, 80 mm
from, the top of the enclosure. The bottom opening must
be within 12 in, 300 mm of, but not less than 3 in, 80 mm
from, the bottom of the enclosure.

All Air From Outside The Building

When installed in a confined space two permanent
openings communicating directly with, or by ducts to,
the outdoors or spaces that freely communicate with the
outdoors must be present. The upper opening must be
within 12 in, 300 mm of, but not less than 3 in, 80 mm
from, the top of the enclosure. The bottom opening must
be within 12 in, 300 mm of, but not less than 3 in, 80 mm
from, the bottom of the enclosure.
Where directly communicating with the outdoors
or communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area
of 1 in 2 /4000 Btu/hr, 550 mm2/kW of the total input
rating of all of the equipment in the enclosure.
Where communicating with the outdoors through
horizontal ducts, each opening shall have a minimum
free area of 1 in2/2000 Btu/hr, 1100 mm2/kW of the
total input rating of all of the equipment in the enclosure.
When ducts are used, they must have the same cross-
sectional area as the free area of the opening to which
they connect.
When calculating the free area necessary to meet the
make-up air requirements of the enclosure, consideration
must be given to the blockage effects of louvers, grills
and screens. Screens must have a minimum mesh size
of 1/4 in, 6.4 mm . If the free area through a louver or grill
is not known ducts should be sized per Table 1 below.
Table 1 Make-up Air Duct Sizing

Required Cross Sectional Duct Area

Input 1/4 in, 6.4 mm
(MBH) Wire Screen
2
in 2 cm
400 100 645 133
968
600 150 200
1290
800 200 267
1000 250 1613 333
1200 300 1935 400
1400 350 2258 467
1600 400 2581 533
2903
1800 450 600
2000 500 3226 667
Metal Wooden
Louvers Louvers
2
in 2 cm in 2 cm
858 400 2581
1290 3871
600
1723 5161
800
2148 1000 6452
2581 1200 7742
3013 1400 9032
3439 1600 10,323
3871 1800 11,613
4303 2000 12,904
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