5894307-UIM-B-0920
16
Johnson Controls Ducted Systems
Note:
Dimensions are those required in Standard ASTM D-3311.
Example:
An 80,000 BTUH furnace requires 32 ft of pipe and five 90º elbows.
Using 2 in. pipe and standard elbows, the total equivalent length is:
This exceeds the 65 ft maximum equivalent length of 2 in. pipe allowed
for that model and is not acceptable.
By using sweep elbows, the total equivalent length is:
This is less than the 65 ft maximum equivalent length of 2 in. pipe
allowed for that model and is acceptable.
Alternatively, using 3 in. pipe and standard elbows, the total equivalent
length is:
This is less than the 90 ft maximum equivalent length of 3 in. pipe
allowed for that model and is acceptable.
Table 5:
Maximum Equivalent Pipe Length
Elevation Sea level–2000
Model Input (BTUH)
Pipe Size (in.)
Max. Equivalent Length (ft)
60,000
2
65
60,000
3
90
60,000
4
150
80,000
2
65
80,000
3
90
80,000
4
150
100,000
2
30
100,000
3
90
100,000
4
150
Elevation 2001–4000
Model Input (BTUH)
Pipe Size (in.)
Max. Equivalent Length (ft)
60,000
2
55
60,000
3
80
60,000
4
145
80,000
2
55
80,000
3
80
80,000
4
145
100,000
2
20
100,000
3
80
100,000
4
145
Elevation 4001–5000
Model Input (BTUH)
Pipe Size (in.)
Max. Equivalent Length (ft)
60,000
2
50
60,000
3
75
60,000
4
140
80,000
2
50
80,000
3
75
80,000
4
140
100,000
2
15
100,000
3
75
100,000
4
140
Elevation 5001–7800
Model Input (BTUH)
Pipe Size (in.)
Max. Equivalent Length (ft)
60,000
2
45
60,000
3
70
60,000
4
135
80,000
2
35
80,000
3
70
80,000
4
135
100,000
2
10
100,000
3
70
100,000
4
135
Figure 18:
Elbow Dimensions
A
A
A
A
STANDARD ELBOW
LONG (SWEEP) ELBOW
Table 6:
Elbow Dimensions
Elbow
A Dimension (Illustrated in Figure 18)
2 in. Standard
2 5/16 in.
3 in. Standard
3 1/16 in.
2 in. Sweep
3 1/4 in.
3 in. Sweep
4 1/16 in.
Table 7:
Equivalent Length of Fittings
Fitting
Equivalent Length
2 in. 90° sweep elbow
5 ft of 2 in. pipe
2 in. 45° sweep elbow
2 1/2 ft of 2 in. pipe
2 in. 90° standard elbow
7 ft of 2 in. pipe
2 in. 45° standard elbow
3 1/2 ft of 2 in. pipe
3 in. 90° sweep elbow
5 ft of 3 in. pipe
3 in. 45° sweep elbow
2 1/2 ft of 3 in. pipe
3 in. 90° standard elbow
7 ft of 3 in. pipe
3 in. 45° standard elbow
3 1/2 ft of 3 in. pipe
4 in. 90° elbow (sweep or standard)
5 ft of 4 in. pipe
4 in. 45° elbow (sweep or standard)
2 1/2 ft of 4 in. pipe
2 in. corrugated connector
10 ft of 2 in. pipe
3 in. corrugated connector
10 ft of 3 in. pipe
4 in. corrugated connector
10 ft of 4 in. pipe
32 ft of 2 in. pipe =
32 equivalent ft
5 - 90º standard 2 in. elbows = (5 x 7) =
35 equivalent ft
Total =
67 equivalent ft of 2 in. pipe
32 ft of 2 in. pipe =
32 equivalent ft
5 - 90º sweep 2 in. elbows = (5 x 5) =
25 equivalent ft
Total =
57 equivalent ft of 2 in. pipe
32 ft of 3 in. pipe =
32 equivalent ft
5 - 90º standard 3 in. elbows = (5 x 7) =
35 equivalent ft
Total =
67 equivalent ft of 3 in. pipe
Table 8:
Combustion Air Intake and Vent Connection Size at Furnace
(All Models)
FURNACE VENT CONNECTION SIZES
Furnace Input
All
Intake Pipe Size
2 in. (5.1 cm)
Vent Pipe Size
2 in. (5.1 cm)
IMPORTANT:
Furnace vent pipe connections are sized for 2 in.
(5.1 cm) pipe. Any pipe size change must be made outside the fur-
nace casing in a vertical pipe section to allow proper drainage of con-
densate. An offset using two 45º (degree) elbows is required for
plenum clearance when the vent is increased to 3 in. (7.6 cm).
