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4.Airband o rairturbulator
settings more o pen t han n ormal.
5.Lockouts onstart-up.
The requirements
forcombustion
and v entilation
airdepend
upon whether furnace is located i n a CONFINED or
UNCONFINED
space.
Unconfined
Space
An unconfined
space
must
have
at least 50 cu ft for each 1,000
BTUH
of total
input
for all the
appliances
(such
as furnaces,
clothes dryers, water
heaters,
etc.) in the space.
In unconfined
spaces
in buildings
of conventional
frame,
brick, or
stone construction,
infiltration
MAY be adequate
to provide
air for
combustion,
ventilation,
and
dilution
of
flue
gases.
This
determination
must be made on an individual
installation
basis and
must
take into consideration
the overall
volume
of unconfined
space,
the
number
of windows
and
ventilation
openings,
the
number
of doors
to the outside,
internal
doors
which can close off
unconfined
space,
and overall
tightness
of building
construction.
Consideration
must
also be given
to the amount
of storage
items
(furniture,
boxes,
etc.) within
the unconfined
space
which
take
away from the air volume.
(Refer to Table 2.)
Table 2 - Minimum
Floor
Area
For Unconfined
Space
FURNACE
MINIMUM
SQ FTWITH
INPUT BTUH
7-1/2
FT CEILING
70,000
467
84,000
560
98,000
654
Many
new buildings
and homes
(and older
ones that have been
weatherized)
MUST
BE considered
as being
of tight construction,
therefore
infiltration
will not be sufficient
to supply
necessary
air
for combustion
and ventilation.
1. Walls
and ceilings
exposed
to outside
atmosphere
have
a
continuous
water
vapor retarder
with a rating
of 1 perm or
less with openings
gasketed
or sealed: and/or
2. Weatherstripping
has been added on operable
windows
and
doors,
and/or
caulking
or sealants
are applied
to areas such
as joints
around
windows
and door
frames;
between
sole
plates and floors: between
wall-ceiling
joints;
between
wall
panels:
at penetrations
for plumbing,
electrical,
and fuel
lines: and at other openings.
If combustion
and
ventilation
air
must
be
supplied
to
an
unconfined
space from outside,
an opening
with a FREE AREA
of
not less
than
1 sq in. per 5,000
BTUH
of total
input
of all
appliances
within
unconfined
space (but not less than 100 sq in.)
must be provided.
This opening
must be located
such that it cannot
be blocked
at any time.
Confined
Space
A confined
space
has a volume
of less than 50 cu ft per 1,000
BTUH
of the total input rating
for all appliances
installed
in that
space.
NOTE:
In calculating
free area, consideration
shall be given
to
blocking
effect of louvers,
grilles,
or screens
protecting
openings.
Screens
used shall not be smaller
than 1/4-in.
mesh and shall be
readily
accessible
for cleaning.
If free area through
a louver
or
grille
is known,
it shall be used in calculating
size and free area
specified.
If design
and free area are not known,
it may be assumed
that wood
louvers
have 20% free area and metal louvers
and grilles
have 60%
free area. Louvers
shall
be fixed
in open
position
or
interlocked
with
furnace
so they
open
automatically
at furnace
start-up
and remain
open during
furnace operation.
The size of the openings
depends
upon whether
the air comes from
outside
of the structure
or an unconfined
space inside the structure.
All Air From Inside the Structure
For a confined
space,
where
air is taken from
an interior
space,
2
permanent
openings
of equal area are required.
WARM
AIR
AIR
CHAUD
457.2mEm
=--_
F--_
T
6"
t
8"
j 203.2mm
-q
i
i
',
......
4
..........
q
@
203;_3m
_
457-2r_1
I
j_
152.4mm
A07642
Fig. 7 - Ventilation
Air Openings
in a Closet Door
The
openings
should
be
located
in
front
of
the
furnace,
approximately
6 in. (152.4
mm) above
the floor
and 6 in. (152.4
mm) below
the ceiling.
Refer
to Fig. 6 for minimum
dimensions
required
and location
of the openings.
All Air From
Outside
of Structure
If outside
air is supplied
to a confined
space,
then the 2 openings
must be equal and located
as above.
1. If combustion
air is taken
through
a permanent
opening
directly
communicating
with the outdoors,
the opening
shall
have a minimum
free area of 1 sq in. per 4.000
BTUH
of
total input rating for all equipment
in the enclosure.
2. If combustion
air is taken
from
outdoors
through
vertical
ducts,
the openings
and ducts MUST
have at least 1 sq in.
of free area per 4,000
BTUH
of the total
input
for all
equipment
within the confined
space. (See Fig. 8 and 9.)
3. If combustion
air is taken from outdoors
through
horizontal
ducts,
the openings
and ducts MUST
have at least 1 sq in.
of free area per 2,000
BTUH
of the total
input
for all
equipment
within the confined
space. (See Fig. 10.)
When
ducts are used to supply
air, they must be of the same cross
sectional
area as free area of openings
to which they connect.
The minimum
dimension
of rectangular
air ducts must
not be less
than 3 in. (76.2 mm).
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