Common Combustion Air Pipe Sizing - Watts Aerco Modulex EXT Series Technical Application Manual

Modulex EXT Vent and Combustion Air Application Guide
EXAMPLES:
1. A 40 foot length of combustion air pipe and 1 sharp 90° elbow plus two termination 90° elbows
add up to 40 ft. + 10 ft. + (2 x 10 ft.) = 70 equivalent ft. (21.3 m).
2. A 30 foot length of combustion air pipe and 2 sharp 90° elbows plus two termination 90°
elbows add up to 30 ft. + (2 x 10 ft.) + (2 x 10 ft.) = 70 equivalent ft. (21.3 m).

2.3. COMMON COMBUSTION AIR PIPE SIZING

Refer to Figures 9 and 10 for typical common combustion air inlet installation. The maximum length is
the sum of the equivalent straight length of horizontal runs, vertical runs, and fittings of the individual
combustion air connector and the common combustion air pipe. The required diameter lengths for a
given Modulex total BTU/hr. Input are shown in Table 4, below.
TABLE 4: Typical Common Combustion Air Run Lengths
TOTAL
COMMON
BTU/HR
VENT
INPUT
DIAMETER
(UP TO AND
INCLUDING)
4"
606,000
(102 mm)
6"
1,284,000
(152 mm)
8"
2,407,500
(203 mm)
10"
3,825,000
(254 mm)
12"
5,355,000
(305 mm)
14"
6,885,000
(358 mm)
16"
9,180,000
(407 mm)
The chart above shows equivalent pipe lengths of the fittings for the common combustion air pipe.
See section 2.2 for equivalent lengths for fittings for the individual boiler connector.
The maximum equivalent length shown is the sum of the equivalent length of the longest individual
connector plus the equivalent length of the common combustion air pipe. If the maximum equivalent
length exceeds 100 equivalent feet, contact your AERCO sales representative or AERCO
International for design assistance and approval.
It is important to use a WYE as a means to connect the individual combustion air pipe into the
common combustion air pipe. This will ensure the least amount of pressure drop. Do NOT use a
TEE, 90°, or 45° elbow.
The maximum pressure drop of the vent is also 100 equivalent feet (30.5 m). Note that this does
NOT mean that the allowed combined pressure drop between the vent and combustion air is 200
equivalent feet (61 m). That is, the vent cannot go above 100 equivalent feet (30.5 m), even if the
combustion air is less than 100 equivalent feet, and vice versa.
TAG-0054_0F
GF-136–V
EQUIVALENT COMMON VENT LENGTHS EXAMPLES
Sharp 90° Sweep 90°
Elbow Elbow
Equiv. Ft (m) Equiv. Ft (m)
10 ft. 5 ft.
(3.05 m) (1.5 m)
10 ft.
N/A
(3.05 m)
10 ft.
N/A
(3.05 m)
10 ft.
N/A
(3.05 m)
10 ft.
N/A
(3.05 m)
10 ft.
N/A
(3.05 m)
10 ft.
N/A
(3.05 m)
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Phone: 800-526-0288
WYE or
Termination
45° Elbow
Tee or
Equiv. Ft (m)
Vent Cap
Equiv. Ft (m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
5 ft. 5 ft.
(1.5 m) (1.5 m)
MAXIMUM LENGTH 
INDIVIDUAL
CONNECTOR
PLUS COMMON VENT
EQUIVALENT FT (M)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
100 ft.
(30.5 m)
Page 13 of 28
09/25/2017