Section 3 — Stack and Intake Vent Sizing and Installation
3-18 Part No. 750-263
Figure 3-8. Two Opening Engineered Method
E. Size the openings by using the formula:
Area in square feet = cfm/fpm
Where cfm = cubic feet per minute of air
Where fpm = feet per minute of air
2. Amount of Air Required (cfm).
A. Combustion Air = 0.25 cfm per kBtuh.
B. Ventilation Air = 0.05 cfm per kBtuh.
C. Total air = 0.3 cfm per kBtuh (up to 1000 feet elevation.
Add 3% more per 1000 feet of added elevation).
3. Acceptable air velocity in the Boiler Room (fpm).
A. From floor to 7 feet high = 250 fpm.
B. Above 7 feet above floor = 500 fpm.
Example: Determine the area of the boiler room air supply openings
for (2) Clearfire 1800 boilers at 750 feet elevation. The air openings
to be 5 feet above floor level.
• Air required: 1800 x 2 = 3600 kBtuh. From 2C above,
3600 x 0.3 = 1,080 cfm.
• Air Velocity: Up to 7 feet = 250 fpm from 3 above.
GAS
VENT
CLEARFIRE
BOILER
WATER
HEATER
GAS
VENT
EXTERIOR WALL
FRESH AIR OPENING
EXTERIOR WALL
FRESH AIR OPENING
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