Bosch 940 ES Installation And Operating Instructions Manual page 18

Installation instructions
Condensate drain requirements
An external condensate drain (not supplied with the heater)
must be installed under the following conditions:
• All vertical terminating vent installations.
• Horizontal terminating vent installations where the total
linear vent length is greater than 10 feet (3.1 m) for 3" and
5 feet (1.5 m) for 4".
• Vent installations where any section of the exhaust vent
pipe passes through an unconditioned space.
Twin pipe termination clearances
The minimum clearance between exhaust vent and combustion
air inlet terminations for twin pipe penetration is 3 feet.
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.
Venting Maximum
allowable
Exhaust pipe
length
3" 28,5 ft
4" 61,25 ft
Table 9 Maximum Allowable Exhaust and Combustion Air
Lengths
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
Max number of elbows
Table 10
18
Maximum Elbow
allowable Equivalency
Combustion air
90°
pipe length
28,5 ft 2,5 ft
61,25 ft 1,25 ft 0,75 ft
3" venting 4" venting
5
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 9 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
90° elbow reduction
sub-total =
45° elbow reduction
Total =
Table 12
For this example, the maximum allowable exhaust pipe length is
45°
23,5 feet.
1,25 ft
Combustion air
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
7
Concentric
1
2
28,5'
- 2,5'
26'
- 2,5'
23,5'
Concentric
2
1
28,5'
- 5'
23,5'
- 1,25'
22,25'
940 ES – 6 720 644 930 (2019/09)