Sears 9MPD - Manual (Page 9)

Figure 5 Outside Air (This is ONLY a guide. Subject to codes of country havingjurisdiction.)
(2) 1 Square Inch per 2000 BTÜH
4. Size openings and ducts per Table 1.
5. Horizontal duct openings require 1 squareinchoffreearea
per 2,000 BTUH of combined input forall gas appliances in
area (see Table 1).
6 . Vertical duct openings or openings directly to outside re­
quire 1 square inch of free area per 4,000 BTUH for com­
bined input of all gas appliances in area (see Table 1).
Tabifi 1 Free Area
BTUH
Input
Rating
h/tinimum Free Area Required for Each Opening
Horizontal Duct
(2,000 BTUH)
Vertical Duct or openings
to outside (4,000 BTUH)
Round Duct
(4,000 BTUH)
50,000 25 sq.in. 12.5 sq. in. 4"
75,000 37.5 sq. in. 18.75 sq. in. 5"
100,000 50 sq.in. 25 sq. in. 6"'
125,000 62.5 sq. in. 31.25 sq. in. 7'
150,000 75 sq.In. 37.5 sq. in. T
EXAMPLE: Determining Free Area
Appliance 1 Appliance 2 Total Input
100.000 + 30,000 = (130,000 - 4,000) = 32.5 Sq. In. Vertical
Appliance 1 Appliance 2 Total Input
100.000 + 30,000 = (130,000 + 2,000) = 65 Sq. In. Horizontal
One permanent opening, commencing within 12" of the top of the
enclosure, shall be permitted where the equipment has clear­
ances of at least 1" from the sides and back and 6" from the front
of the appliance. The opening shall directly communicate with the
outdoors or shall communicate through a vertical or horizontal
duct to the outdoors or spaces (crawl or attic) that freely communi­
cate with the outdoors, and shall have a minimum free area of:
• 1 sq. in per 3000 Btu per hr. of the total input rating of all
equipment located in the enclosure, and
• Not less than the sum of the areas of all vent connectors in
the confined space.
Unconfined Space Installation
CARBON MONOXIDE POISONING HAZARD
Failure to supply additional air by means of ventilation
grilles or ducts could result in death and/or personal
injury.
An unconfined space or homes with tight construction
may not have adequate air infiltration for proper
combustion and ventilation of flue gases.
Most homes will require additional air.
An unconfined space is defined as an area having a minimum vol­
ume of 50 cubic feet per 1,000 Btuh total input rating for all gas
appliances in area. Refer to
Table 2 for minimum area required.
Table 2 Unconfined Space
' ■ Minimum Area in Square Feet
BTUH Input
Rating
Minimum Area in Square Feet
50,000 312
78,000 490
114,000 712
155,000 968
EXAMPLE: NOTE: Square feet is based on 8 foot ceilings.
28.000 BTUH X 50 Cubic Et. = 1.400 = 175Sq. Et.
1,000 8' Ceiling Height
NOTE: Refer to definitions in section titled Unusually Tight
Construction. If any oneof the conditions apply, the space MUST
be considered confined space regardless of size.
1. Adjoining rooms can be considered part of an unconfined
area if there are openings without doors between rooms.
2. An attic or crawl space may be considered an unconfined
space provided there are adequate ventilation openings di­
rectly to outdoors. Openings MUST remain open and NOT
have any means of being closed off. Ventilation openings to
outdoors MUST be at least 1" square of free area per 4,000
BTUH of total input rating for all gas appliances in area.
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