CleaverBrooks ClearFire CFH, Operation, Service And Parts Manual, Page: 40 / 120

Chapter 3 — Flue and Combustion Air Venting
3-12 Part No. 750-295
Example of required air openings (Engineered Method):
Determine the area of the boiler room air supply openings for (2) 60 horsepower Model CFH boilers at 750 feet
elevation. The air openings will be 5 feet above the floor level.
Total boiler horsepower (bhp): 60 x 2 = 120 bhp
From F.3 above, total air required = 120 bhp x 10 = 1200 cfm.
Air Velocity: From G.1 above = 250 fpm.
Area required: From the formula in E above, 1200cfm/250fpm = 4.8 square feet total.
Area/Opening: 4.8 divided by 2 = 2.4 ft
2
per opening (2 required).
Direct Combustion Air - If combustion air will be drawn from
the outside by means of a duct connected directly to the burner
air intake (sometimes referred to as “sealed combustion”), use
the following guidelines:
• Install combustion air duct in accordance with local codes
and the boiler operating and maintenance manual.
• Provide for adequate ventilation of the boiler room or mechanical equipment room.
• Duct material can be PVC or metallic vent material. It should be air tight to prevent in leakage of air
during operation.
• Maximum pressure drop for the duct shall not exceed 0.25" w.c. negative. If this pressure drop is
exceeded a larger size duct is recommended.
• Multiple boilers may be connected to a single duct with take-offs to each boiler.
• If the duct will run horizontally to an outside wall, it is recommended that the duct have a slight
downward slope away from the burner intake to prevent collected moisture from draining into the burner
connection.
• If the outside air is dust-laden or the installation is near a heavily traveled roadway, it is recommended
that an air filter be installed to prevent intake of contaminants that could accumulate on the burner
canister.
Consult local codes, which may supersede these
requirements
Notice