Guidellne to Proper Duct Sizing for Ventllattng An Indoor Electric Grill
These Guidelines are to insure adequate ventilation for an
indoor Electric Grrll. Indoor electric grtlls produce more smoke
than normal cooking and requrres at least 410 CFM to provtde
adequate ventrlation. Less strmgent ventilating requirements
can devrate from these recommendattons.
HORtZONTAL VENTtNG
Figure two on page two shows a direct aischarge to the
outside through a wall rain cap. Due to the lower CFM rating In
thus venting posrtron, duct must be limrted la a maximum of 2
feet of 3% x 10 inch duct capped with a wall rain cap with a free
discharge area of at least 66 inches square. There should be no
bends in the connecting duct between the hood and the wall
rain cap.
Figure 9shows an installation requiring more duct length. A
transrtion to round is used as close to the hood as possible to
eliminate the restriction caused by the 3% x 10 duct. 4S0 bends
should be used instead of 90° bends wherever possrble.
VERTICAL VENTING:
Figure one on page two shows an installation using 3 feet of
3% x 10 inch duct termrnating In a roof rain cap. In table one we
see that 3 feet of 3% x 10 inch duct is the maximum length of 3% x
10 inch duct recommended.
For example, if the straight lengths of duct In Fig 9 total 9 ft.
the elbow is 45O and the roof rain cap has 113 In2 free area,
choose the duct size required. The 45O elbow can be
approximated by dtvtding the equivalent duct lengths In Table 2
by two.
Since we already have 9 ft. of straight duct, Tdble 1 tells us that
7” dia. is too small. So we try 8” dia.
9 ft. Straight Duct
6 ft. Equivalent straight length of 4S0 elbow (8” Dia.)
15 ft.
Fifteen feet is over the maximum of 13 ft. for 8” dia. duct, so 8”
duck is too small.
Move to 9” dia. duct and run through the calculatrons again.
9 ft. Straight Duct,
7 ft. Equivalent strarght length of 9” dia. duct for 45O elbow.
16 ft.
Sixteen feet is under the maximum of 25 ft. for 9” dia. duct, so 9”
duct is a good choice.
TABLE I
Vertical Venttnq
Table I shows the maxrmum length of duct to be
used In conjuncttan with a roof ram cap having a
free area of 113 inz.
TABLE 2
900
Elbow
Duct
Equivalent length of
Size strarght duct of same dia.
7” dia.
l*l ft.
0” dia.
12 ft.
9” dia.
14 ft.
10” dia.
16 ft.
CFM vs. DUCT LENGTH
.25 355 26 61 104
.275 330 34 73 145
.30 250 65 136
.35 180 140
NOTE: The above
table
is
based
on vertical discharge. The values rn this table are for duct length only
and do not account for static pressure loss through roof mounted ram caps.
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