CleaverBrooks ClearFire CFH, Operation, Service And Parts Manual, Page: 39 / 120

Chapter 3 — Flue and Combustion Air Venting
Part No. 750-295 3-11
Engineered Design
-
When determining boiler room air requirements for an unconfined space the
“Engineered Design” method may be used. Following this method, consideration must be given to the size of
the room, airflow and velocity of air as follows:
A. Two permanent air supply openings in the outer walls of the boiler room are recommended. Locate one at
each end of the boiler room, preferably below a height of 7 feet. This allows air to sweep the length of the
boiler (see
Figure 3-9 ).
Figure 3-9 Engineered method
B. Air supply openings can be louvered for weather protection, but they should not be covered with fine mesh
wire, as this type of covering has poor air flow qualities and is subject to clogging with dirt and dust.
C. A vent fan in the boiler room is not recommended as it could create a slight vacuum under certain
conditions and cause variations in the quantity of combustion air. This can result in unsafe burner
performance.
D. It is forbidden to have the total area of the air supply openings at less than one square foot.
E. Size the openings by using the formula (Area in ft
2
= cfm
a
/fpm
a
), where cfm
a
= cubic feet per minute of
air; fpm
a
= feet per minute of air.
F. Amount of air required (cfm):
1. Combustion Air = Maximum boiler horsepower (bhp) times 8 cfm.
2. Ventilation Air = Maximum boiler horsepower (bhp) times 2 cfm.
3. Total Air = 10 cfm per bhp (up to 1000 feet elevation, add 3% more per 1000 feet of added elevation).
G. Acceptable air velocity in the boiler room (fpm):
1. From floor to 7 feet high = 250 fpm.
2. Above 7 feet from boiler room floor = 500 fpm.
EXTERIOR WALL
FRESH AIR OPENING
EXTERIOR WALL
FRESH AIR OPENING
CLEARFIRE ®
BOILER
GAS
VENT