Trane TR250 Service & Installation Manual page 15

(A) ALL AIR SUPPLY FROM INSIDE THE BUILDING:
The confi ned space shall be provided with 2 permanent openings communicating directly with an addi-
tional room(s) of suffi cient volume so that the combined volume of all spaces meets the criteria for an uncon-
fi ned space (a space whose volume is not less than 50 cubic feet per 1,000 btu/hr). The total input of all gas
utilization equipment installed in the combined space shall be considered in making the determination. Each
opening shall have a minimum free area of 1 square inch per 1,000 btu/hr of the total input rating of all gas
utilization equipment in the confi ned space, but not less than 100 square inches. See Table 5. One opening
shall be within 12 inches of the top and and one within 12 inches of the bottom of the enclosure.
(B) ALL AIR SUPPLY FROM OUTDOORS:
The confi ned space shall be provided with 2 permanent
openings, one commencing within 12 inches of the bot-
tom and one commencing within 12 inches of the top of the
enclosure. The opening shall communicate directly, or by
ducts, with the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors.
1. When communicating with the outdoors (either directly
or through vertical ducts), each opening shall have a
minimum free area of 1 square inch per 4,000 btu/hr of
total input rating of all equipment in the enclosure. See
Table 5. When installing a heater below ground (in a
pit), combustion and ventilation air openings must be
provided as shown in Figure 5.
2. When communicating with the outdoors through hori-
zontal ducts, each opening shall have a minimum free
area of 1 square inch per 2,000 btu/hr of total input rat-
ing of all equipment in the enclosure. See Table 5.
3. When ducts are used, they shall be of the same cross-
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular air
ducts shall not be less than 3 inches.
For more detailed methods of provid-
ing air for combustion and ventilation,
refer to the latest edition of the National
Fuel Gas Code (ANSI Z223.1/NFPA 54).
Figure 5: Below-Ground (Pit)
Table 5: Combustion and Ventilation Air Requirements
Free Area per Btu Total Input
Requirement (Btu/hr)
1 sq. in. per 1,000 Btu/hr
(paragraph A)
1 sq. in. per 2,000 Btu/hr
(paragraph B-2)
1 sq. in. per 4,000 Btu/hr
(paragraph B-1)
Installation
Vent Cap
Ventilation
Air Ground Level
Rise of 1 inch
per foot
Drip Tee
Gas Cock
Sediment Trap
Combustion Air Free
Area Required
(sq. in.)
250,000 250
400,000 400
250,000 125
400,000 200
250,000 62.5
400,000 100
15
Combustion
Air
Level Flooring
or Slab
Ventilation Air Free
Area Required
(sq. in.)
250
400
125
200
62.5
100