3
P/N 315-049708FA-4
Figure 2
Recommended Locations in Duct Systems
RETURN
AIR
SUPPLY
AIR
AIR DUCT
HOUSING
AIR DUCT
HOUSING
DAMPER
BLOWER
FILTER
PLENUM
FRESH AIR INTAKE
DAMPER
TYPE A: CLOSED SYSTEM - NO EXHAUST
D
D
TYPE B: PROVISION FOR EXHAUSTING
SOME PERCENTAGE OF RETURN AIR
RETURN
AIR
SUPPLY
AIR
AIR DUCT
HOUSING
AIR DUCT
HOUSING
DAMPER
DAMPER
BLOWER
FILTER
PLENUM
FRESH AIR INTAKE
DAMPER
D
D
EXHAUST AIR
OUTPUT
DAMPER
TYPE C: RETURN AIR UNDER POSITIVE PRESSURE
FROM SEPARATE BLOWER
EXHAUST AIR
OUTPUT
DAMPER
RETURN
AIR
SUPPLY
AIR
AIR DUCT
HOUSING
RETURN AIR
BLOWER
AIR DUCT
HOUSING
DAMPER
DAMPER
BLOWER
FILTER
PLENUM
FRESH AIR INTAKE
DAMPER
D
D
Figure 1
Typical Mounting of Duct Housing
OUTLET
TUBE
INPUT
SAMPLING
TUBE
CENTER
LINE
OF DUCT
CL
MOUNTING THE AIR DUCT HOUSING
Location on Duct System
This guideline contains general information on duct smoke
detector installation, but does not preclude the NFPA
documents listed. Siemens Industry, Inc. assumes no
responsibility for improperly installed duct detectors. To
determine the correct installation position for an 8741, 8742
or 8743 duct smoke detector, the following factors must be
considered.
1) A uniform non-turbulent (laminar) airflow between 100 ft/
min. to 4,000 ft/min. must be present in the HVAC duct.
To determine duct velocities, examine the engineering
specifications that define the expected velocities or use
an Alnor model 6000AP velocity meter (or equivalent).
