Model 4
1500 - 6000 MBTU/hr
Rev. 03-08
Section B2-18
room is neutral or slightly positive
pressure),
or with a direct vent to outside the
boiler room where
air is drawn
directly
from the
exterior
of the building.
R
e
gardless
of the
method,
all
installations
must
comply
with
NFPA
54 (National
Fuel Gas
Code
-
NFGC)
for U.S. installations and
CAN/CSA
B149/.1 and B149.2 for Canadian
installations.
Engineered Design
- When
determining
boiler room air
requirements
for the boiler,
the
"Engineered Design" method
may be
used. Following
this method,
consid
era
t
ion
must be
given
to the
size
of the boiler room, airflow, and air
velocity
as follows:
A. Two
permanent
air supply
openings
in the outer walls of the boiler room are
recommended. Locate one
at
each end
of the
boiler
room,
preferably below
a height
of 7 feet. This
allows
air to
sweep
the
length
of the boiler.
Refer
to
Figure
B2-3.
B. Air supply
openings
can be
louvered
for
weather protection,
but they should not
be
covered
with a fine
mesh
wire,
as
this
type
of
covering has poor
air flow qualities
and is
subject
to
clogging
with dirt and dust.
C.
A vent fan in the boiler room is not
recommended
as it could create a slight
vacuum under certain conditions
and
cause variations
in the quantity of combustion
air. This can result in
unsafe burner
performance.
D. It is
forbidden
to
have
the total
area
of the air supply
openings
at
less
than one
square
foot.
E.
Size
the
openings
by
using
the formula
(Area
in ft
2
=
cfm
a
/fpm
a
),
where
cfm
a
=
cubic feet per minute of air; fpm
a
=
feet per minute of air.
F.
Amount
of air
required
(cfm):
1.
Combustion
Air
=
Maximum boiler
horsepower
(bhp) times 8 cfm.
2.
Ventilation
Air
=
Maximum boiler
horsepower
(bhp) times 2 cfm.
3. Total Air
=
10 cfm per bhp (up to 1000 feet
elevation,
add 3%
more
per
1000
feet of
added
elevation).
G.
Acceptable
air
velocity
in the boiler
room
(fpm):
1.
From
floor to 7 feet high
=
250 fpm.
2.
Above
7 feet from boiler
room
floor
=
500 fpm.
Example
of
required
air
openings (Engineered
Method):
Determine
the
area
of the boiler room air supply
openings
for [2]
size
4500 Model
4 boilers at 750 feet
elevation;
each
have
a rating of 107 boiler horsepower. The
air
openings
will be 5 feet
above
the floor level.
The
total boiler
horsepower
(bhp): 107 x 2
=
214 bhp.
From
F.3
above,
total air
required
=
214 bhp x 10
=
2140 cfm.
Air
Velocity: From
G.1
above
=
250 fpm.
Area
required: From the formula in E
above,
2140 cfm/250 fpm
=
8.56 square
feet total.
Area opening:
8.56 divided by 2
=
4.28 ft
2
per
opening
(2 required).
Notice
Consult local codes, which may supersede these
req
u
ire
m
en
ts.
See Table
B2-15 for
combustion
air and flue
gas
flow.
To Next Page
Loading...
Need help?
General
