MG3P Installation Manual

8
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 10 sq. In 4 inches
60,000 15 sq. In 5 inches
80,000 20 sq. In 5 inches
100,000 25 sq. In 6 inches
120,000 30 sq. In 6 inches
140,000 35 sq. In 7 inches
160,000 40 sq. In 8 inches
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Ducts must
extend above
attic insulation.
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Ventilation Louvers
at each end of attic
Attic
Insulation
12" Max
Furnace
Water
Heater
Vent or
Chimney
Figure 4. Combustion Air Drawn from Outside
Through Vertical Ducts
Figure 2. Combustion Air Drawn from Inside
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 100 sq. In 12 inches
60,000 100 sq. In 12 inches
80,000 100 sq. In 12 inches
100,000 100 sq. In 12 inches
120,000 120 sq. In 13 inches
140,000 140 sq. In 14 inches
160,000 160 sq. In 15 inches
Vent or
Chimney
Furnace
Water
Heater
12” Max.
12” Max.
See
Notes
See
Notes
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.
Water
Heater
Vent or
Chimney
- - - - - - - - -
- - - - - - - - -
Furnace
Ventilation Louvers For
Unheated Crawl Space
- - - - - - - - -
Inlet Air
Ventilation Louvers
(each end of attic)
NOTE: Air openings shall
each have a free area of
not less than one square
inch per 4,000 Btuh of the
total input rating of all
equipment in the enclosure
.
- - - - - - - - -
Alter
nate
Air Inlet
Outlet
Air
Figure 3. Combustion Air Drawn from a Crawl
Space or Vented Attic
Figure 5. Combustion Air Drawn from Outside
Through Horizontal Ducts
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 20 sq. In 5 inches
60,000 30 sq. In 6 inches
80,000 40 sq. In 7 inches
100,000 50 sq. In 8 inches
120,000 60 sq. In 9 inches
140,000 70 sq. In 10 inches
160,000 80 sq. In 10 inches
Furnace
Water
Heater
Air Ducts must be
at least 1 sq. in.
per 2,000 Btuh of
total input rating.
Vent or
Chimney
Air Duct
Air Duct
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 Figure
5 (page 8).
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 square inches. If the combined input rate of
all appliances is 120,000 Btuh, each opening must have a
free area of at least 120 square inches.
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.
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. Attics or
crawl spaces must connect freely with the outdoors if they are
the source of air for combustion and ventilation. See Figure 4.