Specifications

Page 22 of 40 12/03/2013
Benchmark Series Boilers
Venting and Combustion Application Guide
GF-2050
TAG-0022_0S
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913 • Ph: 800-526-0288
1.21.1 BMK 1500 Example:
Calculate the maximum pressure drop for a single boiler installation at 500 feet above sea level
having a winter design temperature of 20°F. The duct system consists of:
1) An 6-inch diameter exhaust vent with three 90° elbows, two 45° elbows, 50 feet of
horizontal run, 20 feet of vertical run
2) A rain cap termination
3) A 6-inch diameter ducted combustion air duct with two 90° elbows and 50 feet of run
CALCULATION:
6-inch Diameter Exhaust Vent Pressure
Two 90° elbows: 2 x 13.11 = 26.22 ft
One 45° elbow: 1 x 9.98= 9.98 ft
35 feet total run
(5 horizontal + 20 vertical):25 x 1.70 = 42.50 ft
Rain cap exit loss: 1 x 21.95 = 21.95 ft
Vent drop subtotal: = 100.65 ft
Altitude correction: 100.65 = 102.49 ft
0.982 (CF)
Natural draft for 20 feet @ 20°F outside temperature: = 12.6 ft
Altitude correction:-12.6 x 0.982 CF = -12.37 ft
Total vent drop: = 90.12 ft
6-inch Diameter Combustion Air Duct Pressure
Two 90° elbows: 2 x 5.84 = 11.68 ft
50 feet total run: 20 x 1.06 = 21.20 ft
Entrance loss: 1 x 8.60 = 8.60 ft
Combustion air drop subtotal: = 41.48 ft
Altitude correction: = 41.48 = 42.24 ft
0.982 CF
Combustion air drop total: = 42.24 ft
System total pressure drop
Vent drop + combustion air duct pressure drop
= 90.12 + 42.24
= 132.36 ft
Conclusion:
Pressure drop is less than 140 equivalent feet. System OK.