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.
I
These Guidelines
are to insure adequate
ventilation
for an
indoor Electric Grtll. Indoor electric grills produce more smoke
than normal cooking and requires at least
410
CFM to provrde
adequate
ventilation.
Less stringent
ventilating
requirements
can deviate from these recommendations.
HORIZONTAL
VENTING
Figure two on page two shows a direct drscharge
to the
outside through
a wall rain cap. Due to the lower CFM rating in
this venting posrtion.
duct
must be ltmited to 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 Sshows an installation
requiring
more duct length. A
transition
to round is used as close to the hood as possible t0
eliminate
the restriction
caused by the 3% x 10 duct. 4S" bends
should be used instead of 90° bends wherever
possible.
VERTICAL
VENTING:
figure
one on page two shows an installation
using 3 feet of
3% x 10 inch duct terminating
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
45i" elbow
can
be
approximated
by dividing the equivalent
duct lengths in Table2
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 45O elbow (8" Dia.)
15 ft.
Fifteen feat is over the maximum
of 13 ft. for 8" dia. duct, so 8"
duct is to small.
Move to 9" dia. duct and run through
the calculations
again.
9 ft. Straight
Duct.
7 ft. Equivalent
straight
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.
FIGURE 9
TABLE I
Vertical Venting
I-G-l-I
Size
1
3% x 10"
7" dia.
8" dia.
9" dta.
10" di;
Max.
I I
Duct
I
I
I
I
Length
(Feet1
3
7
13
25
40
Table I shows the maximum
length of duct to be
used in conjunction
with a roof rain cap having a
free area of 113 it-P.
TABLE 2
Duct
Equivalent
length of
Size
straight duct of same dia.
7" dia.
11 ft.
0" dia.
12 ft.
9w
9" dia.
14 ft.
Elbow
10" dia.
16 ft.
CFM vs. DUCT LENGTH
Equivalenf Duct Length (ft.)
Static
Pressure
CFM
3-X x 10 &act.
7" dia.
6" dia.
9" dia.
.06
460
4
a.5
17
30
.lO
440
7
16.0
31
55.5
.15
417
12
25.0
50
da
.20
390
18
40
77
142
.2s
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 in this table are for duct length only
and do not account
for static pressure loss through
roof mounted
rain caps.
Page 4
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