CAC / BDP BW4BAH-91, Installation, Operation & Maintenance Manual

7

Provide enough fresh air to assure proper combustion. 
Fire in the boiler uses oxygen. It must have continuous 
supply. Air in the house contains only enough oxygen to 
supply burner for short time. Outside air must enter the 
house to replace air used by the burner. Study the following 
examples 1 and 2 to determine your fresh air requirements.

EXAMPLE 1: Boiler Located in Unconfi ned Space

If your boiler is in an open area (un-partitioned basement) 
in conventional house, air that leaks through cracks around 
doors and windows will usually be adequate to provide air 
for combustion. Doors should not 

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 t tightly. Do not caulk 

cracks around windows.
An uncon

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 ned space is de

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 ned as space whose volume is 

not less than 50 cubic feet per 1,000 Btu per hour of total 
input rating of all appliances installed in that space.

EXAMPLE 2: Boiler Located in Confi ned Space

A. 

All Air from Inside the Building:

 Con

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 ned 

space shall be provided with two permanent openings 

communicating directly with additional room(s) of suf

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 cient 

volume so the combined volume of all spaces meets the 

criteria for uncon

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 ned space. Total input of all combustion 

equipment installed in combined space shall be considered 

in making this determination. Each opening shall have 

minimum free area of one square inch per 1,000 Btu per 

hour of total input rating of all combustion equipment in the 

con

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 ned space, but not less than 100 square inches. One 

opening shall be within 12 inches of top and one within 12 

inches of bottom of the enclosure.

Example: Your boiler is rated at 100,000 Btu per hour. 

Water heater is rated at 30,000 Btu per hour. Total is 

130,000 Btu per hour. You need two grilles, each with 130 

square inches of FREE opening. Metal grilles have about 

60% FREE opening. To 

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 nd louvered area needed, multiply 

free opening required by 1.7 (130 x 1.7 = 221.0 sq. in. 

louvered area). In this example, two grilles each having 8” 
x 30” (240 sq. in.) louvered area would be used.

FRESH AIR FOR COMBUSTION

 WARNING

Asphyxiation, 

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 re hazard. Do not obstruct air 

openings to combustion area. Follow instructions 

below, to maintain adequate combustion air.

!

NOTICE

Install outside air intake if you use 

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 replace or 

kitchen or bathroom exhaust fan. These devices rob 

boiler and water heater of combustion air.

Figure 4 - Air Openings For Boiler Located In 

Confi ned Space (Utility Room

)