Sears N8MPL050B12B1 - Manual (Page 10)

The opening shall commence within 12" of the top of the enclo­
sure. Appliances shall have clearances of at least 1 ' from the sides
and back and
6" from the front. The opening shall directly commu­
nicate with the outdoors or shall communicate through a vertical or
horizontal duct to the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors.
4. Combination of Indoor and Outdoor Air shall have:
a. Indoor openings that comply with the Indoor Combus­
tion Air Method below and
b. Outdoor openings located as required in the Outdoor
Combustion Air Method above and
c. Outdoor openings sized as follows.
1) Calculate the Ratio of all Indoor Space volume divid­
ed by required volume for Indoor Combustion Air Meth­
od. Outdoor openings sized as follows.
2) Outdoor opening size reduction Factor is 1 minus the
Ratio in 1) above.
3) Minimum size of Outdoor openings shall be the size
required in Outdoor Combustion Air Method above
multiplied by reduction Factor.
Tabic 1
Free Area
BTUH
Input
Rating
Minimum Free Area Required for Each Opening or Duct to Outdoors
Two Horizontal Ducts
(sq. in./2,000 BTUH)
Single Opening
(sq. in./3,000 BTUH)
Two Vertical Ducts or Openings
(sq. in.M,000 BTUH)
Round Duct
(sq. in. /4,000
BTUH)
50,000 25 sq. in. 16.7 sq. in. 12.5 sq. in. 4"
75,000 37.5 sq. in. 25 sq.in. 18.75 sq. in. 5"
100,000 50 sq. in. 33.3 sq. in. 25 sq. in. 6"
125,000 62.50 sq. in. 41.7 sq. in. 31.25 sq. in. T
150,000 75 sq. in. 50 sq.in. 37.5 sq. in. T
EXAMPLE: Determining Free Area
Furnace Water Heater Total Input
100.000 + 30,000 = (130,000-4,000) = 32.5 Sq. In. Vertical
Furnace Water Heater Total Input
100.000 + 30,000 = (130,000-2,000) = 65 Sq. In. Horizontal
Indoor Combustion Air
Standard and Known-Air-Infiltration Rate Methods
© NFPA & AGA
Indoor air is permitted for combustion and ventilation, if the
Standard or Known-Air-Infiltration Rate Method is used.
A WARNING
CARBON MONOXIDE POISONING HAZARD.
Failure to supply adequate combustion air couid
result in death or personal injury.
Most homes will require additional air from outdoors
for combustion and ventilation. A space with at least
50 cubic feet per 1,000 BTUH input rating or homes
with tight construction may need outdoor air to
supplement air infiltration for proper combustion
and ventilation of flue gases.
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