Outdoor Air From A Crawl Space Or Vented Attic; Outdoor Air Using Vertical Ducts; Outdoor Air Using Horizontal Ducts - Oxbox J951X U Series Installation Instructions Manual

EXAMPLE
If the combined input rate of all appliances is less than or
equal to 100,000 Btuh, each opening must have a free
area of at least 100 in . If the combined input rate of all
2
appliances is 120,000 Btuh, each opening must have a
free area of at least 120 in
Vent or
Chimney
NOTES:
Each opening must be
at least 100 sq. in. or
1 sq. in. per 1,000 Btuh
of total input rating,
whichever is greater.
Openings must start at
no more than 12 inches
from the top and bottom
of the enclosure.
TOTAL INPUT MINIMUM FREE AREA
RATING (BTUH) (EACH OPENING)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
Figure 2. Combustion Air Drawn from Inside

Outdoor Air from a Crawl Space or Vented Attic

When the openings can freely exchange air with the outdoors,
each opening shall have a minimum free area of 1 square
inch per 4,000 Btuh of total appliance input. The openings
shall exchange directly, or by ducts, with the outdoor spaces
(crawl or attic) that freely exchange with the outdoors. See
.
Figure 3 (page 8)
Vent or
Chimney
Outlet
Air
Furnace
Inlet Air
Alternate
Air Inlet
Ventilation Louvers For
Unheated Crawl Space
Figure 4. Combustion Air Drawn from a Crawl
Space or Vented Attic
8
2 .
12" Max.
Water
Heater
Furnace
See
Notes
12" Max.
ROUND DUCT
DIAMETER
100 sq. In 12 inches
100 sq. In 12 inches
100 sq. In 12 inches
100 sq. In 12 inches
120 sq. In 13 inches
140 sq. In 14 inches
160 sq. In 15 inches
Ventilation Louvers
(each end of attic)
NOTE: Air openings shall
each have a free area of
Water
not less than one square
Heater
inch per 4,000 Btuh of the
total input rating of all
equipment in the enclosure.

Outdoor Air Using Vertical Ducts

If combustion air is taken from outdoors through vertical
ducts, the openings and ducts must have a minimum free
area of one square inch per 4,000 Btuh of total appliance
input. See
Figure 4 (page 8)

Outdoor Air Using Horizontal Ducts

If combustion air is taken from outdoors through horizontal
ducts, the openings and ducts must have a minimum free
area of one square inch per 2,000 Btuh of total appliance
input. Ducts must have cross - sectional area at least as
large as the free area of their respective openings to the
furnace space. See
Ventilation Louvers
at each end of attic
See
Vent or
Notes
Chimney
TOTAL INPUT
RATING (BTUH)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
Figure 3. Combustion Air Drawn from Outside
Through Vertical Ducts
Vent or
Chimney
TOTAL INPUT
RATING (BTUH)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
Figure 5. Combustion Air Drawn from Outside
Through Horizontal Ducts
.
Figure 5 .
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
Attic
total input rating.
Insulation
Ducts must
extend above
attic insulation.
Water
Furnace
Heater
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
12" Max
MINIMUM FREE AREA
(EACH OPENING)
10 sq. In
15 sq. In
20 sq. In
25 sq. In
30 sq. In
35 sq. In
40 sq. In
Air Duct
Water
Air Ducts must be
Heater
at least 1 sq. in.
Furnace
per 2,000 Btuh of
total input rating.
Air Duct
MINIMUM FREE AREA
(EACH OPENING)
20 sq. In
30 sq. In
40 sq. In
50 sq. In
60 sq. In
70 sq. In
80 sq. In
ROUND DUCT
DIAMETER
4 inches
5 inches
5 inches
6 inches
6 inches
7 inches
8 inches
ROUND DUCT
DIAMETER
5 inches
6 inches
7 inches
8 inches
9 inches
10 inches
10 inches