Bosch Therm C 1210 ES Installation And Operating Instructions Manual page 18

Installation instructions
Minimum combustion air and exhaust pipe length
The minimum exhaust pipe length is 1 foot (0.3m) of straight
vent pipe. The minimum combustion air pipe length is one 90°
elbow.
Maximum combustion air and exhaust pipe length
The following tables display the maximum allowable straight
pipe lengths for combustion air and exhaust piping with
consideration to the number of elbows used. Reduce the
equivalent length for each elbow used from the maximum
allowable length depending on the system used. Refer to
table 8 if using 3" diameter venting. Refer to table 9 if using 4"
diameter venting.
3" Maximum
Venting allowable
Exhaust
pipe length
Twin pipe 31ft
system
Concentric 23ft
system
Table 8 Maximum Allowable Exhaust and Combustion Air
Lengths for 3" venting
4" Maximum
Venting allowable
Exhaust pipe
length
Twin pipe 63ft
system
Concentri 43ft
c system
Table 9 Maximum Allowable Exhaust and Combustion Air
Lengths for 4" venting
Use of elbows
It is recommended to limit the amount of elbows used in the
exhaust and combustion air piping to reduce friction in the air
flow. The following lists the maximum amount of 90° elbows
allowed in either the exhaust or combustion air piping:
Max. number of 90° elbows 3" venting
Twin pipe system
Concentric system
Table 10
18
Combustion Elbow
air pipe Equivalency
length
90° 45°
31ft 5 ft
23ft 5 ft
Combustion Elbow
air pipe Equivalency
length
90° 45°
63ft 2.5ft
43ft 2.5ft
4" venting
5 7
4 7
Two 45° elbows are equal to one 90° elbow. Any
combination of 45° and 90° elbows may be used in the vent
system as long as the combination does not exceed the
maximum listed in table 10 above.
Calculation example for 3" venting:
Exhaust
System used
Number of 90° elbows needed:
Number of 45° elbows needed:
Table 11
Calculation of example
Max. length
3 ft
90° elbow reduction
3 ft sub-total =
45° elbow reduction
Total =
Table 12
For this example, the maximum allowable exhaust pipe length is
12 feet.
1.5ft
Combustion air
1.5ft
System used
Number of 90° elbows needed:
Number of 45° elbows needed:
Table 13
Calculation of example
Max. length
90° elbow reduction
sub-total =
45° elbow reduction
Total =
Table 14
Concentric
Concentric
C 1210ES/ESC – 6 720 644 887 (2022/04)
1
2
23'
- 5'
18'
- 6'
12'
2
1
23'
- 10'
13'
- 3'
10'