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Figure 23B - Top View of 3-1/4" x 10" Adapter
in two positions
Model # RD310
3-3/8"
CALCULATING CUBIC FEET PER MINUTE (C.F.M.)
Based on the blower position, determine the
required straight duct length and size, and the
number and types of elbows or transitions.
Calculate the total equivalent length using this
equation: A+B = C
A = Duct fitting equivalent straight length (use Table 1,
Page 17).
B = Straight duct length of smallest duct used.
C = Total equivalent straightlength of the smallest size
ducting used.
Use the value of C from Chart 1, Page 16 (Internal
Blower) or Chart 2 (Remote Blower) to determine the
C.F.M.
NOTE: We recommend a minimum of 350 cubic
feet per minute (C.F.M.) Flow for the range
downdraft system.
FOR EXAMPLE: An internal ventilation system, using
model VTN30RQ, would have a total equivalent length of
45 feet when using fittings noted on Page 17.
C L
10-3/4"
➛
BLOWER DUCT SIZING
Figure 24
Studs Located on Bottom of
Gasket
Plenum
Adapter
Adapter Mounting
Bracket
A. Duct Fitting Equivalent
Quantity
Fitting
Description
1
6" Dia to 3-1/4" x 10"
2
3-1/4" x 10" 90° elbows
(2 @ 10 feet)
1
3-1/4 x 10" Wall cap
(Model# 12551)
Total "A" Duct Fitting Equipment 23 Ft.
B. Straight Duct Length
1
15 Ft.of 3-1/4 x 10"
rectangular duct
1
1 Ft. of 3-1/4" x 10"
rectangular duct
1
6 Ft. of 3-1/4 x 10"
rectangular duct
Total "B" Straight Duct Length
C. Total Equivalent Straight =23+22=45 Ft.
Once you've determined the value of C, refer to Chart 1
for internal blower (Page 16) to find the minimum C.F.M.
for 3-1/4" x 10" rectangular duct. Note that the chart
legend furnishes different lines for different ducting sizes
and shapes. By using the correct line, you can see that 45
feet of rectangular duct equates to approximately 420
C.F.M.
15
Exhaust Plenum
Equivalent
Length
1 Ft.
20 Ft.
2 Ft.
15 Ft.
1 Ft.
6 Ft.
22 Ft.
I
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