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Total Input
Rating (Btuh)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
Round Duct
Diameter
12"
12"
12"
12"
13"
14"
15"
Minimum
Free Area
(Each Opening)
100 sq. in.
100 sq. in.
100 sq. in.
100 sq. in.
120 sq. in.
140 sq. in.
160 sq. in.
Furnace
12" Max.
12" Max.
Water Heater
Vent or
Chimney
Each opening must
be at least 100 sq. in.
or 1 sq. in. per 1000
Btuh of total input
rating, whichever is
greater. See minimum
area per table.
Figure 11. Equipment in a Confi ned Space
with all Combustion Air drawn from Inside
Figure 10. Protective Screen for
One Pipe Installations
Protective
Screen
Upfl ow Models
Downfl ow Models
Figure 8. Furnace on a Wood Floor
Figure 9. Downfl ow Sub-Base
Dimensions
Downflow
Wood
Sub-base
Floor
Furnace
Sheet
Metal
Plenum
1 inch thick fiberglass 3 lb density
28.38"
9.25"
19.63"
3"
19.75"
or 14.25"*
or 22.50"**
2.0"
1.58"
1.50"
16.75"
or 11.25"
18.75"
or 13.25" or 21.50"*
* RL 040/060
** RL 120