specified. Where the louver and grille design and free area are not know, it shall be assumed that wood louvers have a 25 percent free area, and met louvers and grilles have 75 percent free area.
Screens
Minimum Screen Mesh Size:
Screens shall not be smaller than 1/4 “ mesh.
Motorized Louvers:
Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to opening during burner startup and to shut down the main burner if the louver close during burner operation.
Combustion Air Ducts
Combustion air ducts shall comply with the following:
Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength and rigidity.
Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.
Ducts shall serve a single space.
Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving the upper and lower combustion air openings shall be maintained to the source of combustion air.
Ducts shall not be screened where terminating in an attic space.
Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air.
For informational purposes, there are several codes that address the amount of air and/or size of the opening(s) in walls for combustion air.
NFPA 54, National Fuel Gas Code (ANSI Z223.1)
ASME
ASME Section VI, Recommended Rules for Care and Operation of Heating Boilers
6
Date: 8-4-2010
Revision: 0
Form: 2396
BOCA, National Mechanical Code
WARNING:
Do not locate air intakes where petroleum distillates, CFC’s, detergents, volatile vapors or any other chemicals are present. Severe boiler corrosion and failure will result.
1.7FLUE GAS VENTING SYSTEM
WARNING:
The
1.7.1DESIGN & INSTALLATION
A qualified venting professional experienced in venting system designs should design the boiler vent system. The vent size must be NO LESS THAN 8” IN DIAMETER and sized such that the pressure drop between the boiler and the point of discharge does not exceed 0.20” WC. While the vent must be UL Listed Special Gas Vent per Category Code DGSH or DGSH7 for Canada, Bryan Steam, LLC recommends the use of venting components fabricated from