Bryan Boilers AB Series, Installation, Operation & Service Manual

ESTIMATING FLUE GAS FLOW RATE (ACFM) 
Flue gas volumetric flow rate in SCFM (standard cubic 
feet per minute) and ACFM (actual cubic feet per 
minute) can be estimated by using the information in 
1.8.1A.  Divide the Total Input of appliances 
connected to the chimney or vent by 1000. Then 
multiply this result times the factor listed in the SCFM 
and ACFM table. The ACFM data is required for 
determining stack exit velocity and induced draft fan 
requirements. 
 
ESTIMATING STACK EXIT VELOCITY 
First, determine the ACFM for the stack as described 
above. Multiply the total ACFM times the Velocity 
Factor from the Velocity Table in Table 1.8.1B for the 

stack diameter used. The result is the Stack Exit 
Velocity in feet per second. 
ESTIMATING STACK EMISSIONS 
Table 1.8.1C lists approximate emissions of NOx 
(oxides of nitrogen) and CO (carbon monoxide). The 
table lists both the concentration, in parts per million 
(ppm),  and the flow rate, in pounds per hour (PPH), of 
each compound: Divide the total input of appliances 
connected to the chimney or vent by 1,000,000. Then 
multiply this result times the value listed in the table for 
PPH emissions. 
 
MANUAL REFERENCES 
See Figure 1.8.1 for a graphics listing of applicable 
sections of this manual for each section of the vent 
system.

FIGURE 1.8.1: VENT DESIGN INSTRUCTIONS - REFERENCE 

TABLE 1.8.1A: ESTIMATING FLUE GAS VOLUMETRIC FLOW RATE

Approximate Flue Gas VOLUMETRIC FLOW RATE (Per 1000 Btu/hr Input) 

(Multiply factor listed times boiler input in MBH) 

BOILER TYPE 

SCFM Per 

1000 Btu/hr INPUT 

ACFM Per 

1000 Btu/hr INPUT 

APPROXIMATE FLUE GAS 

TEMPERATURE AT FULL 

INPUT 

Water & 15# Steam 

Boilers 

Before Draft 

Control 

After Draft 

Control 

Before Draft 

Control 

After Draft 

Control 

Before Draft 

Control 

After Draft 

Control 

Atmospheric Gas 

(Draft Diverter) 

Atmospheric Gas 

(Barometric D.R.) 

0.250 

0.250 

0.364 

0.280 

0.462 

0.462 

0.546 

0.474 

480 F 

480 F 

350 F 

430 F 

150# Steam Boilers 

Before Draft 

Control 

After Draft 

Control 

Before Draft 

Control 

After Draft 

Control 

Before Draft 

Control 

After Draft 

Control 

Atmospheric Gas 

(Draft Diverter) 

Atmospheric Gas 

(Barometric D.R.) 

0.250 

0.250 

0.364 

0.280 

0.486 

0.486 

0.602 

0.517 

550 F 

550 F 

400 F 

500 F