Specification

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Draft
Draft Control
Simple rules of thumb to guide size selections:
1. For most applications, the draft control should be the
same size as the flue pipe. In other words, use a 6"
control for a 6" pipe.
2. If the vent pipe or breach is square, use the round
equivalent. For example - on a 14" x 14" breach use a 14"
control. Little flow occurs in the corners of a square pipe,
so its capacity is approximately the same as a round pipe
of the same diameter.
3. If the breach is rectangular
or oval, compute its cross-
sectional area and select a
draft control having the same
or a greater nominal cross-
sectional area. A breach 14"
high x 10" wide would have
a cross-sectional area of 140
square inches. From Table
1, select a 14" control with a
cross-sectional area of 154
square inches.
4. Where a control larger than
32" is required, use more
than one draft control with
combined cross-sectional
areas equal to or greater than
that of the breach.
5. When chimneys are of an
unusual height, or if the draft
to be maintained is either
very high or very low, it is
advisable to deviate from the
rules of thumb outlined here
and refer to the sizing chart.
Choosing The Right Size
Table 1
Control
Size
Nominal
Cross-Sectional Area
(Sq. In.)
Control
Size
Nominal
Cross-Sectional Area
(Sq. In.)
6"
28
16"
201
7"
38
18"
255
8"
50
20"
314
9"
63
24"
452
10"
78
28"
616
12"
113
32"
804
14"
154
Sizing Chart
Diameter of
Vent or Breach
If Chimney
Height is
Use This
Size Control
If Chimney
Height is
Use This
Size Control
If Chimney
Height is
Use This
Size Control
4"
15' or less 4" 16' or more 5"
5"
15' or less 5" 16' or more 6"
6"
15' or less 6" 16' or more 7"
7"
15' or less 7" 16' or more 8"
8"
15' or less 8" 16' or more 9"
9"
15' or less 9" 16'-30' 10" 31' or more 12"
10"
20' or less 10" 21'-40' 12" 41' or more 14"
11"
20' or less 12" 21'-40' 12" 41' or more 14"
12"
20' or less 12" 21'-40' 14" 41' or more 16"
13"
22' or less 14" 23'-45' 16" 46' or more 18"
14"
22' or less 14" 23'-45' 16" 46' or more 18"
15"
22' or less 16" 23'-45' 16" 46' or more 18"
16"
30' or less 16" 31'-50' 18" 51' or more 20"
17"
30' or less 18" 31'-50' 20" 51' or more 20"
18"
30' or less 18" 31'-50' 20" 51' or more 20"
19"
30' or less 20" 31'-50' 20" 51' or more 24"
20"
30' or less 20" 31'-50' 20" 51' or more 24"
21"
30' or less 20" 31'-50' 24" 51' or more 24"
22"
30' or less 24" 31'-50' 24" 51' or more 24"
23"
35' or less 24" 36'-60' 24" 61' or more 28"
24"
35' or less 24" 36'-60' 24" 61' or more 28"
25"
35' or less 28" 36'-60' 28" 61' or more 28"
26"
40' or less 28" 41'-70' 28" 71' or more 28"
27"
40' or less 28" 41'-70' 28" 71'-100' 28"
28"
50' or less 28" 51'-100' 32" 100' or more 32"
29"
50' or less 28" 51'-100' 32" 100' or more 32"
30"
50' or less 32" 51'-100' 32" 100' or more 32"
31"
50' or less 32" 51'-100' 32" 100' or more Two 24"
32"
50' or less 32" 51'-100' 32" 100' or more
One 24"
One 28"
33"
50' or less 32" 51'-100'
One 32"
One 20"
100' or more
One 32"
One 24"
34"
50' or less 32" 51'-100'
One 32"
One 24"
100' or more
One 32"
One 24"
Sizing the Control