Whirlpool RGH 8300-2 - Manual (Page 2)

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Guideline fo Proper Duct Sizing for Ventilating An Indoor Electric Grill
These Guidelines are to insure adequate ventilation for an indoor
Electric Grill. Indoor electric grills produce more smoke than
normal cooking and requires at least410CFM to provide adequate
ventilation. Less stringent ventilating requirements can deviate
from these recommendations.
HORIZONTAL VENTING;
Figure 2 on page 1 shows a direct discharge to the outside
through a wall rain cap. Due to the lov/erCFM rating in this venting
position, duct must De limited to a maximum of 2 feet of 3'/* x 10
inch duct capped v/ith 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.
VERTICAL VENTING:
Figure 1 on page 1 shows an installation using 3 feet of 3% x 10
inch duct terminating in a roof rain cap. In table 1 we see that 3 feet
of 3'.i X 10 inch duct is the maximum length of 3>4 x 10 inch duct
recommended.
Figure 7 shews an installation requiring more duct length. A
transition to round is used as close to the hood as possible to
eliminate the restriction caused by the 3'i x 10 duct.
45:1 bends
should be used instead of 90^ bends wherever possible.
For example, ifthestraightlengthsofductinFig.7 total 9 ft. the
elbow IS 45 ^ and the roof ram cap has 113 in' free area, choose the
duct size required. The 45’' elbow can be approximated by dividing
the equivalent duct lengths in Table 2 by two.
Since we already have 9 ft. of straight duct, Table 1 tells us that 7"
dia. IS too small. So we try 8" dia.
9 ft. Straight Duct ‘
6 ft. Equivalent straight length of 45° elbow (8" Dia.)
15 ft.
Fifteen feet 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 45° 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 Venting
Duct
Size
3'4
X
10" 7" d.ia. 8" dia. 9" dia. 10" dia.
Max
Duct
Length
(Feet)
3 7 . 13 25 40
Table 1 shows the maximum length of duct to be used in
conjunction witn a roof ram cap having a free area of 113 m'.
TABLE 2
Duct
Size
Equivalent length of
straight duct of same dia.
7" dia. 11 ft.
8" dia. 12 ft.
—
9" dia. 14 ft.
90°
Elbow
10" dia. 16 ft.
CFM vs. DUCT LENGTH FOR RGH SERIES HOOD
Equivalent Duct Length (ft.)
Static
Pressure
CFM
3-% X 10
Reel.
7" dia. 8" dia. 9" dia.
.06 460 4 8.5 17 30
.10 440 7 16.0 31 55.5
.15 417 12
j
25.0 50 88
.20
! i i
390 18 1 40 ! 77
i 1 1
142
.25 355 26 I 61 1 104
.275 330
1 1
34 1 73 j ■' 145
.30
1 ' '
250 1 65 I ■ 136 !
1 ' !
T R ! 1 Й П i z n
! ! !
NOTE; The above table is based on- vemc-al disc iTLe. The values
m this table are for duct length only and со not account tor static
□ rassure loss throuoh roof mounted ram c. ps.