Residential smoke alarms located near air returns and supplies?

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sw_ross

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Can someone direct me to info about requirements for locating an alarm near a supply or return? I know it’s not NEC. Just trying to figure out how far to stay away from Hvac supplies and returns. Is it in the installation instructions or building code?
Thanks
 
Check and see if your jurisdiction has adopted NFPA 72. In CA it's incorporated into the Residential Code.

29.8.3.4 Specific Location Requirements
6. Smoke alarms and smoke detectors shall not be installed within a 36 in. (910 mm) 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.
 
Joe.B said:
Check and see if your jurisdiction has adopted NFPA 72. In CA it's incorporated into the Residential Code.

29.8.3.4 Specific Location Requirements
6. Smoke alarms and smoke detectors shall not be installed within a 36 in. (910 mm) 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.
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In Montana, so not sure about that adoption.
That only applies to supplies, not returns?
 
Joe.B said:
6. Smoke alarms and smoke detectors shall not be installed within a 36 in. (910 mm) 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.
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So is it 3' or outside of the direct flow or both?
 
I don’t know if there’s a difference between supply air and return air when it comes to a negative affect on performance.

One would supposedly push the smoke away and the other draw it towards it if it’s in the path of the register.
 
farmantenna said:
just make sure you're after the HVAC guy so you can see their location. be careful with paddle fans.
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Nobody enforcing this around here other than fire marshal on non residential buildings when a fire alarm system is required.

From past experiences in dwellings (I usually install smoke alarms even though nobody is enforcing it) a smoke alarm in a small bedroom with a paddle fan, is probably mostly useless if the fan is running, no matter where you place it. Even high on a wall is impacted by the fan if it is running. So you kind of just ignore the fan.

At same time locating it in a dead air space is pretty useless.

Still having something in there is better protection than nothing.
 
I think it's more about the concentration of smoke than its movement. The HVAC supply will dilute the smoke near it with fresh(er) air, and the return will concentrate it, but a ceiling fan will merely circulate it.
 
I always thought this was about dust. Ever notice how the dust builds up on the blades of a fan? I assumed that placing the detector near a fan or a register would cause dust to build up on the sensor...
 
Joe.B said:
I always thought this was about dust. Ever notice how the dust builds up on the blades of a fan? I assumed that placing the detector near a fan or a register would cause dust to build up on the sensor...
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Dust accumulates on fan blades due to the slight electrostatic charge that builds up on the blade as it moves through the air.
I’m not sure if the velocity of air moving across the sensor is high enough to have the same result, but I kind of doubt it.
 
ptonsparky said:
Well, you should be cleaning the SD occasionally. Maybe do the fans the same time you change batteries.
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I get calls for false alarms, and even have had them in my own house. I tell them to stick the vacuum cleaner hose up to it and suck out all the dust, insects, etc. If you read instructions they actually say you need to do this periodically.
 
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