18
Installation on a concrete slab.
1. Create an opening in the fl oor according to the
dimensions in Figure 16.
2. Position the plenum and the furnace as shown in
Figure 17.
CIRCULATING AIR REQUIREMENTS
WARNING:
Do not allow combustion products to enter the
circulating air supply. Failure to prevent the
circulation of combustion products into the
living space can create potentially hazardous
conditions including carbon monoxide
poisoning that could result in personal injury
or death.
All return ductwork must be secured to
the furnace with sheet metal screws. For
installations in confi ned spaces, all return
ductwork must be adequately sealed. When
return air is provided through the bottom of the
furnace, the joint between the furnace and the
return air plenum must be air tight.
The surface that the furnace is mounted on must
provide sound physical support of the furnace
with no gaps, cracks or sagging between the
furnace and the fl oor or platform.
Return air and circulating air ductwork must
not be connected to any other heat producing
device such as a fi replace insert, stove, etc.
This may result in fi re, explosion, carbon
monoxide poisoning, personal injury, or
property damage.
Plenums and Air Ducts
• Plenums and air ducts must be installed in accordance
with the Standard for the Installation of Air Conditioning
and Ventilating Systems (NFPA No. 90A) or the
Standard for the Installation of Warm Air Heating and
Air Conditioning Systems (NFPA No. 90B). Additional
reference information for US and Canadian installations
can be found in the Duct Systems section (page 5).
• Tables 4 and 5 (pages 30-32) contain the airfl ow and
temperature rise data. If the maximum airfl ow is 1,600
CFM or more, it is recommended that two openings
be used for return air on upfl ow furnaces. Downfl ow
furnaces can only use one return opening.
• It is recommended that the outlet duct contain a
removable access panel. The opening should be
accessible when the furnace is installed in service and
shall be of a size that smoke or refl ected light may be
observed inside the casing to indicate the presence of
leaks in the heat exchanger. The cover for the opening
shall be attached in such a manner as to prevent
leaks.
• If outside air is used as return air to the furnace for
ventilation or to improve indoor air quality, the system
must be designed so that the return air is not less than
Figure 17. Furnace on a
Concrete Slab
Concrete
Floor
Furnace
Sheet
Metal
Plenum
*SL MODEL
NUMBERS:
Dimension
“A”
Dimension
“B”
054D-24B
16
⅝
19
¼
072D-24B
16
⅝
19
¼
090D-35C
20
⅛
19
¼
120D-45D
23
⅝
19
¼
“A”
“B”
Opening in concrete floor
Figure 16. Cutout Dimensions
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