Equivalent Duct Lengths for Commonly Used Transitions
Duct Piece
Smooth
Straight
3¼" x 10"
Straight
3¼" x 14"
Straight
90° Elbow
Round
45° Elbow
Round
3¼" x 10"
90° Elbow
Round
3¼" x 10"
45° Elbow
Round
3¼" x 10"
Flat Elbow
Round to
3¼" x 10"
3¼" x 10"
to Round
Round to
3¼" x 10"
90° Elbow
Size of Duct
Equivalent
Piece (in)
Length (ft)
6
1.2
7
0.95
8
0.7
10
0.6
N/A
1
N/A
0.7
6
12
7
8
8
6
6
5
7
4
8
3
N/A
5
N/A
15
N/A
20
6
1
7
1
6
5
7
3
6
10
7
8
Duct Piece
3¼" x 10"
to Round
90° Elbow
3¼" x 10"
Center Reverse
Elbow Left
3¼" x 10"
Center Reverse
Elbow Right
3¼" x 10" Left
Reverse Elbow
3¼" x 10"
Right Reverse
Elbow
Round
Wall Cap
Round
Roof Cap
2' Long
3¼" x 10"
Flex
3¼" x 10"
to Round
7" Inline
Backdraft
Damper
3¼" x 10"
Roof Jack
and Shutter
NOTE: These commonly used installation parts can be purchased
at a local hardware store. THERMADOR® does not manufacture all
these parts.
Size of Duct
Equivalent
Piece (in)
Length (ft)
6
10
7
5
N/A
15
N/A
25
N/A
15
N/A
25
6
2
7
2
8
2
10
2
6
2
7
2
8
2
N/A
20
10
1
7
N/A
Table 3: Duct Lengths
English 7