Step 3—Confined Space
A confined space has a volume of less than 50 cu ft per 1000 Btuh
of the total input rating for all appliances installed in that space. A
confined space MUST have 2 permanent openings, 1 within 12 in.
of the ceiling, and the other within 12 in. of the floor which freely
communicate with an unconfined space or the outdoors. (See Fig.
17 or 18.)
NOTE:
In determining the free area of an opening, the blocking
effect of the louvers, grilles, and screens must be considered. If the
free area of a louver or grille design is unknown, it may be
assumed 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 the air comes from
outside of the structure or an unconfined space inside the structure.
ALL AIR FROM INSIDE THE STRUCTURE
1. Each opening MUST have at least 1 sq in. of free area per
1000 Btuh of the total input for all equipment within the
confined space, but not less than 100 sq in. per opening. (See
Fig. 17.) The minimum dimension of air openings shall not be
less than 3 in.
2. If the building is constructed unusually tight, in addition to the
2 permanent openings that freely communicate with an
unconfined space, a permanent opening directly communicat-
ing with the outdoors should be provided. This opening shall
have a minimum free area of 1 sq in. per 4000 Btuh of total
input rating for all equipment in the enclosure.
3. If the furnace is installed on a raised platform to provide a
return-air plenum, and return air is taken directly from the
hallway or space adjacent to the furnace, all air for combustion
must come from outdoors. (See Fig. 17.)
ALL AIR FROM OUTSIDE THE STRUCTURE
1. If combustion air is taken from outdoors through vertical
ducts, the openings and ducts MUST have at least 1 sq in. of
free area per 4000 Btuh of the total input for all equipment
within the confined space. (See Fig. 18.)
2. If combustion air is taken from outdoors through horizontal
ducts, the openings and ducts MUST have at least 1 sq in. of
free area per 2000 Btuh of the total input for all equipment
within the confined space. (See Fig. 18.)
3. When ducts are used, they must be of the same cross-sectional
area as the free area of the openings to which they connect.
The minimum dimension of ducts must not be less than 3 in.
(See Fig. 18.)
INSTALLATION
Step 1—Leveling Legs (If Desired)
When furnace is used in upflow position with side inlet(s), leveling
legs may be desired. (See Fig. 19.) Install field-supplied,
corrosion-resistant 5/16-in. machine bolts and nuts.
NOTE:
The maximum length of bolt should not exceed 1-1/2 in.
1. Position furnace on its back. Locate and drill a 5/16-in.
diameter hole in each bottom corner of furnace. (See Fig. 19.)
Holes in bottom closure panel may be used as guide locations.
2. For each hole, install nut on bolt and then install bolt and nut
in hole. (Install flat washer if desired.)
3. Install another nut on other side of furnace base. (Install flat
washer if desired.)
4. Adjust outside nut to provide desired height, and tighten inside
nut to secure arrangement.
NOTE:
Bottom closure must be used when leveling legs are used.
See Bottom Closure Panel section.
Step 2—Installation in Upflow and Downflow
Applications
NOTE:
For downflow applications, this furnace is approved for
use on combustible flooring when special base (available from
manufacturer) Part No. KGASB0201ALL is used. Special base in
not required when this furnace is installed on manufacturer’s Coil
Assembly Part No. CD5 or CK5, or Coil Box Part No. KCAKC is
used.
1. Determine application being installed from Table 1.
2. Construct hole in floor per dimensions specified in Table 1
and Fig. 20.
3. Construct plenum to dimensions specified in Table 1 and Fig.
20.
4. If downflow subbase (KGASB) is used, install as shown in
Fig. 21.
If Coil Assembly Part No. CD5 or CK5 or Coil Box Part No.
KCAKC is used, install as shown in Fig. 22.
For Example:
MINIMUM FLOOR AREA FOR UNCONFINED SPACE
58MSA Furnace
Input Btuh
Minimum Sq Ft With
7-1/2 Ft Ceiling
40,000
267
60,000
400
80,000
533
100,000
667
120,000
800
For Example:
COMBUSTION AIR FROM UNCONFINED SPACE
58MSA Furnace
Input Btuh
Free Area per Opening
(Sq In.)
40,000
100
60,000
100
80,000
100
100,000
100
120,000
120
For Example:
COMBUSTION AIR FROM OUTDOORS THROUGH
VERTICAL DUCTS
58MSA Furnace
Input Btuh
Free Area per Opening
(Sq In.)
Round Pipe
(In. Dia)
40,000
10.0
4
60,000
15.0
5
80,000
20.0
6
100,000
25.0
6
120,000
30.0
7
For Example:
COMBUSTION AIR FROM OUTDOORS THROUGH
HORIZONTAL DUCTS
58MSA Furnace
Input Btuh
Free Area per Opening
(Sq In.)
Round Pipe
(In. Dia)
40,000
20.0
6
60,000
30.0
7
80,000
40.0
8
100,000
50.0
8
120,000
60.0
9
15
