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).