Unconfined Space; Confined Space - Carrier 58DXT Operating Instructions Manual

RETURN
AIR
INTERIOR
HEATED
SPACE
SUPPLY AIR
* Minimum opening size is 100 sq in. with
minimum dimensions of 3 in.
†
Minimum of 3 in. when type B-1 vent is used.
Fig. 3—Confined Space: Air for Combustion and
Ventilation from an Indoor Unconfined Space
The requirements for combustion and ventilation air depend upon
whether furnace is located in a CONFINED or UNCONFINED
space.

UNCONFINED SPACE

An unconfined space must have at least 50 cu ft for each 1000
Btuh of input for all appliances (such as furnaces, clothes dryer,
water heaters, etc.) in the space.
For Example:
58DXT FURNACE
HIGH-FIRE INPUT
BTUH
63,000
84,000
105,000
If the unconfined space is constructed unusually tight, air for
combustion and ventilation MUST come from either the outdoors
or spaces freely communicating with outdoors. Combustion and
ventilation openings must be sized the same as for a confined
space as defined below. Return air must not be taken from the
room unless equal or greater amount of air is supplied to the room.

CONFINED SPACE

A confined space is defined as a space whose volume is less than
50 cu ft per 1000 Btuh of total input ratings of all appliances
installed in that space. A confined space MUST have provisions
for supplying air for combustion, ventilation, and dilution of flue
gases using 1 of the following methods.
VENT THROUGH ROOF
(CATEGORY I)
12" MAX
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
UNCONFINED
SPACE
6" MIN
†
(FRONT)
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
12" MAX
A93387
MINIMUM SQ FT
WITH
7-1/2 FT CEILING
420
560
700
DUCTS TO
OUTDOORS
12" MAX
1 SQ IN.
RETURN
A
PER 2000
AIR
BTUH *
DUCTS
TO
OUTSIDE
1 SQ IN.
B
PER 2000
BTUH *
12" MAX
SUPPLY AIR
* Minimum dimensions of 3 in.
NOTE: Use any of the following
combinations of openings:
A & B C & D
Fig. 4—Confined Space: Air for Combustion and
Ventilation from Outdoors
NOTE: In determining free area of an opening, the blocking
effect of louvers, grilles, and screens must be considered. If free
area of louver or grille design is unknown, assume that wood
louvers have a 20 percent free area and metal louvers or grilles
have a 60 percent free area. Screens, when used, must not be
smaller than 1/4-in. mesh. Louvers and grilles must be constructed
so they cannot be closed.
The size of the openings depends upon whether air comes from
outside of the structure or an unconfined space inside the structure.
1. All air from an unconfined space inside the structure requires
2 openings (for structures not usually tight):
a. Each opening MUST have at least 1 sq in. of free area per
1000 Btuh of total input for all equipment within the
confined space, but not less than 100 sq in. per opening.
(See Fig. 3 and Table 2.) The minimum dimension of air
openings shall not be less than 3 in.
b. If the building is constructed unusually tight, a permanent
opening directly communicating with the outdoors shall be
provided. (See item 2 below.)
c. If furnace is installed to obtain return air is taken directly
from hallway or space adjacent to furnace, all air for
combustion must come from outdoors.
2. Air from outside the structure requires 1 of the following
methods:
a. If combustion air is taken from outdoors through 2 vertical
ducts, the openings and ducts MUST have at least 1 sq in.
of free area per 4000 Btuh of total input for all equipment
within the confined space. (See Fig. 4 and Table 2.)
5
1 SQ IN.
PER 4000
BTUH
*
D 12"
MAX
VENT
F
THROUGH
ROOF
(CATEGORY I)
1 SQ IN.
PER 4000
BTUH
OUTDOORS
1 SQ IN.
PER 4000
BTUH
G
E
12"
MAX
C
12" MAX
DUCT
1 SQ IN.
TO
PER 4000
OUTDOORS
BTUH
D & E F & G
*
*
A93388