smoke alarms and return vents

[Richard W. Washington]

Originally Posted by jwicklander

Smoke alarms and detectors shall not be installed within 36 inches horizontal path from the supply registers and should also be installed out of the direct airflow from those registers. Same thing with ceiling fans...36 inch horizontal path from the tip of the blades.

The commercial duct smokes have two pipes mounted on surface of the detector that poke into the duct. The airflow acts as a vacuum and a continuous sample of air goes through the detector. Any evidence of smoke shuts that unit down and system goes into alarm.

Good point about the ceiling fans. Never thought of that. Is that a manuf. or NFPA requirement?

[Jeffrey R. Wicklander]

From the 2007 version of the NFPA code ...

NFPA 72
11.5.1.1*
Where required by applicable laws, codes, or standards for
a specific type of occupancy, approved single- and multiple-station
smoke alarms shall be installed as follows:
(1)*In all sleeping rooms and guest rooms
(2)*Outside of each separate dwelling unit sleeping area, within
6.4 m (21 ft) of any door to a sleeping room, the distance measured
along a path of travel
(3) On every level of a dwelling unit, including basements
(4) On every level of a residential board and care occupancy
(small facility), including basements and excluding crawl spaces and
unfinished attics
(5)*In the living area(s) of a guest suite
(6) In the living area(s) of a residential board and care occupancy
(small facility)

11.8.3.5
Specific Location Requirements. The installation of smoke
alarms and smoke detectors shall comply with the following
requirements:
(1) Smoke alarms and smoke detectors shall not be located where
ambient conditions, including humidity and temperature, are outside
the limits specified by the manufacturer's published instructions.
(2) Smoke alarms and smoke detectors shall not be located within
unfinished attics or garages or in other spaces where temperatures can
fall below 4°C (40°F) or exceed 38°C (100°F).
(3) Where the mounting surface could become considerably warmer or
cooler than the room, such as a poorly insulated ceiling below an
unfinished attic or an exterior wall, smoke alarms and smoke detectors
shall be mounted on an inside wall.
(4) Smoke alarms and smoke detectors installed within a 6.1 m (20 ft)
horizontal path of a cooking appliance shall be equipped with an
alarm-silencing means or be of the photoelectric type.
(5) Smoke alarms and smoke detectors shall not be installed within a
914 mm (36 in.) horizontal path from a door to a bathroom containing a
shower or tub.
(6) Smoke alarms and smoke detectors shall not be installed within a
914 mm (36 in.) horizontal path from the supply registers of a forced
air heating or cooling system and shall be installed outside of the
direct airflow from those registers.
(7) Smoke alarms and smoke detectors shall not be installed within a
914 mm (36 in.) horizontal path from the tip of the blade of a
ceiling-suspended (paddle) fan.
(8 Where stairs lead to other occupied levels, a smoke alarm or smoke
detector shall be located so that smoke rising in the stairway cannot
be prevented from reaching the smoke alarm or smoke detector by an
intervening door or obstruction.
(9) For stairways leading up from a basement, smoke alarms or smoke
detectors shall be located on the basement ceiling near the entry to
the stairs.
(10)* For tray-shaped ceilings (coffered ceiling) smoke alarms and
smoke detectors shall be installed on the highest portion of the
ceiling or on the sloped portion of the ceiling within 305 mm (12 in.)
vertically down from the highest point.

Jeff

[Paul W. Abernathy]

Smoke Detectors shall not be installed within 3' of supplies, returns, ceiling fans and what have you. The smoke detector that is placed in a duct is a duct detector and it is usually placed on the return.