The minimum
clearances
to combustion
construction
MUST
be
maintained
between
the furnace
and adjacent
construction,
as
shown
in Figure
1.
In addition
to clearances
in Figure
1, clearance
for the vent pipe
must be considered.
A su bbase for combustible
floors MUST be used when the furnace
is installed
on combustible
material.
See "9. DuctworkandFilter't
GAS SUPPLY
Typical Downflow
Installation
RETURN
AIR
SUPPLY
AIR
25-24-38
3. Combustion
& Ventilation
Air
CARBON MONOXIDE POISONING HAZARD.
evaluated carefully as it may be necessary to provide outdoor air
for combustion.
Failure
to
provide
adequate
combustion
and
ventilation
air could
result
in
death
or
personal
injury.
Use
methods
described
here
to
provide
combustion
and ventilation
air.
Furnaces
require
ventilation
openings
to provide
sufficient
air for
proper
combustion
and ventilation
of flue gases.
All duct or open-
ings for supplying
combustion
and ventilation
air must comply
with
the gas codes,
or in the absence
of local codes,
the applicable
na-
tional codes.
Combustion
and ventilation
air must be supplied
in accordance
with one of the following:
1.
Section
8.3, Air for Combustion
and Ventilation,
of the National
Fuel Gas Code,
(NFGC),
ANSI
Z223.1-2002/NFPA
54-2002
in the U.S.,
2. Sections 7.2, 7.3, 7.5, 7.6, 7.7, and 7.8 of National Standard of
Canada,
Natural
Gas
and
Propane
Installation
Code
(NSCNGPIC), CSA B149.1-05
in Canada,
3.
Applicable
provisions
of the local building
code.
•
Commercial
buildings.
•
Buildings
with indoor
pools.
•
Furnaces
installed
in laundry
rooms.
•
Furnaces
installed
in hobby
or craft rooms.
•
Furnaces
installed
near chemical
storage
areas.
•
Permanent
wave
solutions
for hair.
•
Chlorinated
waxes
and cleaners.
•
Chlorine
based
swimming
pool chemicals.
•
Water
softening
chemicals.
•
De-icing
salts or chemicals.
•
Carbon
tetrachloride.
•
Halogen
type
refrigerants.
•
Cleaning
solvents
(such as perchloroethylene).
•
Printing
inks, paint removers,
varnishes,
etc.
•
Hydrochloric
acid.
•
Sulfuric
Acid.
•
Solvent
cements
and glues.
•
Antistatic
fabric
softeners
for clothes
dryers.
•
Masonry
acid washing
materials.
Outdoor Combustion Air Method
A space having
less than 50 cubic feet per 1,000 BTUH input rating
for all gas appliances
installed
in the space requires
outdoor
air for
combustion
and ventilation.
When the installation
is complete,
check
that all appliances
have
adequate
combustion
air and are venting
properly.
See
Venting
And Combustion
Air Check in "4. Gas Vent Installation
"Section
in
this manual.
Air Openings and Connecting
Ducts
1.
Total input rating for all gas appliances
in the space
MUST be
considered
when
determining
free area of openings.
Contaminated Combustion Air
Installations
in certain areas or types of structures
could cause ex-
cessive
exposure
to contaminated
air having
chemicals
or halo-
gens that will result
in safety and performance
related
problems
and may harm the furnace.
These
instances
must use only out-
door air for combustion.
The following
areas or types of structures
may contain
or have ex-
posure
to the substances
listed
below.
The installation
must
be
2.
Connect
ducts or openings
directly
to the outdoors.
3.
When
screens
are used
to cover
openings,
the openings
MUST
be no smaller
than
1/4" mesh.
4.
The minimum
dimension
of air ducts MUST
NOT be less than
3 _ .
When
sizing
a grille,
louver,
or screen
use the free area
of
opening.
If free area is NOT stamped
or marked
on grill or lou-
ver, assume
a 20%
free area
for wood
and 60%
for metal.
Screens
shall have a mesh size not smaller
than 1/4".
441 01 2314 02
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