15
COMBUSTION AND VENTILATION AIR (cont.)
For improved indoor air quality, added safety and product per-
formance we recommend direct vent type installations. If non-di-
rect type vent system is used, the requirements for combustion
air must be provided as identified in the National Fuel Gas Code.
Combustion air requirements are determined by whether the fur-
nace is in an open (unconfined) area or in a confined space such
as a closet or small room.
FURNACE LOCATED IN AN UNCON-
FINED SPACE
USING INDOOR AIR FOR COMBUSTION:
An unconfined space must have at least 50 cubic feet for each
1,000 BTUH of total input for all appliances in the space.
Table 1
below specifies minimum space requirements and a few exam-
ples of the room sizes required for different inputs. The sizes are
based on 8-foot ceilings.
If the open space containing the furnace is in a building with tight
construction, outside air may still be required for the furnace to
operate and vent properly. Outside air openings should be sized
the same as for a confined space.
FURNACE LOCATED IN A CONFINED
SPACE
A confined space is defined as any space for a given furnace input
rating which is smaller than that which is specified in
Table 1
as
minimum for an “
unconfined
” space. If the space is less than that
specified in this table, the space is defined as
“confined”.
If the space is small enough to be designated as “confined”, it
must have openings into the space which are located in accor-
dance with the requirements set forth in the following subsections
A and B. Size connected to the heated area or to the outside, and
by the input of
ALL
appliances in the space.
If the confined space is within a building with tight construction,
combustion air must be taken from outdoors or from an area
freely communicating with the outdoors.
A. USING INDOOR AIR FOR COMBUSTION:
IMPORTANT:
Air should not be taken from a heated space
with a fireplace, exhaust fan or other device that may pro-
duce negative pressure.
If combustion air is taken from the heated area, the openings
must each have at least 100 square inches of free area.
Each opening must have at least one square inch of free
area for each 1,000 BTUH of total input in the space.
Table 2
shows some typical examples of openings required for com-
bustion air openings required for a confined space.
B. USING OUTDOOR AIR FOR COMBUSTION:
IMPORTANT:
Do not take air from an attic space that is
equipped with power ventilation.
The confined space must communicate with the outdoors in
accordance with Methods 1 or 2 below. The minimum dimen-
sion of air openings shall not be less than 3 inches. Where
ducts are used, they shall be of the same cross-sectional
area as the free area of the openings to which they connect.
METHOD 1:
Two permanent openings, one located within 12 inches of the
top and one located within 12 inches of the bottom of the en-
closure, shall be provided. The openings shall communicate
directly, or by ducts, with the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors.
Co
m
bu
stio
n A
ir
COMBUSTION AIR REQUIREMENTS: CONFINED AND
UNCONFINED SPACES
!
WARNING
ALL FURNACE INSTALLATIONS MUST COMPLY WITH
THE NATIONAL FUEL GAS CODE, NFPA 54 AND LOCAL
CODES TO PROVIDE ADEQUATE COMBUSTION AND
VENTILATION AIR FOR THE FURNACE. FAILURE TO DO
SO CAN RESULT IN EXPLOSION, FIRE, PROPERTY DAM-
AGE, CARBON MONOXIDE POISONING, PERSONAL IN-
JURY OR DEATH.
!
WARNING
READ AND FOLLOW THE
GENERAL VENTING REQUIRE-
MENTS AND GUIDELINES
OF THIS MANUAL FOR ADDI-
TIONAL VENTING REQUIREMENTS PERTAINING TO ALL
FURNACE INSTALLATIONS (INCLUDING DIRECT AND
NON-DIRECT VENTING). FAILURE TO FOLLOW ALL IN-
STRUCTIONS IN THIS MANUAL CAN RESULT IN EQUIP-
MENT FAILURE, EQUIPMENT DAMAGE, PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
TABLE 7:
MINIMUM SPACE REQUIREMENTS
FOR UNCONFINED SPACE, NON-DIRECT VENT*
Input
(BTUH)
Minimum
Space
(Cubic Ft)
Minimum Area
with 8
Ceilings (sq )
Typical Room
Size w/ 8'
Ceilings ( x )
50,000
2,500
313
16 x 20
75,000
3,750
470
24 x 20
100,000
5,000
625
32 x 20
125,000
6,300
790
36 x 30
150,000
7,500
940
32 x 30
TABLE 1: MINIMUM SPACE REQUIREMENTS
FOR UNCONFINED SPACE, NON-DIRECT VENT
30
TABLE 8: MINIMUM FREE AREA
OPENING REQUIRED FOR A
FURNACE LOCATED IN A
CONFINED SPACE USING
INDOOR AIR FOR COMBUSTION.
Input (BTUH)
Free Area for Each
Opening (sq inches)
50,000
100
75,000
100
100,000
100
125,000
130
150,000
150
TABLE 2: MINIMUM FREE AREA
OPENING REQUIRED FOR A
FURNACE LOCATED IN A
CONFINED SPACE USING
INDOOR AIR FOR COMBUSTION.
