NFPA 72 states that a smoke detector cannot be located within 3 feet of an A/C supply register.

Where does it state that a smoke alarm cannot be located within 3 feet of a A/C return?

It doesn't. Section 11.8.3.5(6) only identifies SUPPLY registers & not those used for return.

And to me, this makes sense. The supply registers would tend to blow the smoke away from the alarms whereas the return registers may tend to draw the smoke towards alarm.

I have noted that a few of the installation instructions provided with smoke alarms RECOMMEND a 3' clearance from BOTH the supply & resturn registers.

From the KIDDE FYRNETICS Smoke Alarm installation instructions:

Thanks Bryan. That is what I thought - that it isn't specified the codes for "return." But we can use 110.3(B) for that.

I am amazed at how many smoke alarms I find on rough-in that are within 3 feet of either.

Bryan I have a follow-up question for you (or anyone) if I may. Which code do I use to allow myself to enforce NFPA 72 with regard to smoke alarm placement? In other words, is it triggered by the FBC? or FBC-R? or NEC? If so, where? Thanks.

2007 FBC-R:




In addition to that, the FBC-B references the NFPA 72 in several sections:

Thanks Bryan!

Here is the section on specific locaions from NFPA 72 (2006,I believe):

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.

What I see a lot os SD's close to the kitchen and right outside bathrooms...
And I was surprised about the 36" from a paddle fan but it makes sense if it's on.

The 100 degree thing surprises me. I bet it is easy to get 100 degrees in a tray ceiling, even with the AC on unless they have a return up there.

I agree.

One of the big "flaws" with smoke alarm location requirements is that all the places where a fire is likely to originate are all the places a smoke alarm shouldn't be. Kitchens, garasge, attic spces, etc.

It's a balancing act between providing adequate protection while reducing the potential for nuisance alarms...

I was bored so I started going through the 2012 IBC - Residential. There is a requirement for a smoke alarm in a "habitable" attic but not an "unhabitable" attics.

?

So then I had to go into definitions to see what it was:

ATTIC, HABITABLE. A finished or unfinished area, not considered a story, complying with all of the following requirements:

1. The occupiable floor area is at least 70 square feet (17 m2), in accordance with Section R304,

2. The occupiable floor area has a ceiling height in accordance with Section R305, and

3. The occupiable space is enclosed by the roof assembly above, knee walls (if applicable) on the sides and the floor-ceiling assembly below.


I love codes. The requirements just keep getting better and better........and better........and better.