Smoke detector locations

[Renegomez]

Can a smoke detector be located within 36'' of an a/c return vent? The 2010 NFPA 72 A.29.8.3.4(6) refers to supply registers of a forced air only.

 

[Gregg Harris]

Can a smoke detector be located within 36'' of an a/c return vent? The 2010 NFPA 72 A.29.8.3.4(6) refers to supply registers of a forced air only.

Yes but not supply

 

[Dennis Alwon]

Yes but not supply

mY understanding is that it cannot be near a supply nor a return but I have heard arguments both ways

 

[ron]

That requirement in NFPA 72 is in the Annex, not the main body of the code. The Annex is not enforceable. It says it in the first paragraph of the Annex.

There is no requirement for separation from airflow.

In high airflow environments, there is a reduction of detector spacing.

 

[Gregg Harris]

mY understanding is that it cannot be near a supply nor a return but I have heard arguments both ways

2010 NFPA 72

29.8.3.3

#6 Smoke alarms and detectors shall not be installed within a 36 inch horizontal path from the "supply registers" of a forced air heating and cooling system and shall be installed outside of the direct airflow from those registers.

Now there are some jurisdiction that have adopted local ordinances requiring the 36 inches from the return registers and contradicts new testing technology and being current with manufactures instalation instructions,

1999 adition had both supply and return dimensions listed.

 

[G._S._Ohm]

I have heard arguments both ways

If there is smoke in the duct work the detector may work better when next to a supply duct by monitoring the whole building.
If it's near a return duct the duct may pull smoke from the vicinity across the detector and so it also works better.
Smoke rises, so clean air coming from or going into a duct may make the detector less sensitive.

It seems that moving air makes the detector more sensitive to its location. With still air you can count on smoke rising.

In this case the rule that works better most of the time for most structures may be the best.

ASHRAE can help with this as far as the movement of air.

 

[gadfly56]

In NJ we're on the 2007 edition of NFPA 72.

5.7.5.3.2 Location. Smoke detectors shall not be located di-
rectly in the airstream of supply registers.

There is mention of a 36" spacing requirement in Chapter 11 [11.8.3.5 (5), (6), and (7)], but Chapter 11 doesn't apply to commercial, business, industrial, or educational facilities, among others. The title is "Single- and Multiple-Station Alarms and Household Fire Alarm Systems". However, my experience is that AHJ's apply the rule universally. As a result I automatically apply this spacing requirement. I haven't seen a job yet where observing this restriction was a hardship.

On return air, if you look at System Sensor's installation manual for the 2W-B detector, it does, in fact, mention not to install "near fresh air inlets or returns", among other locations.

 

[bobbymari]

I have installed near returns with no problems, inspectors even take a closer look to make sure its not a supply and this has been in a few different cities. if theres access and i dont have to swiss cheese the walls i try to stay away from both but still have yet to be called on any near a return

 

[bobbymari]

there are numerous apt bldgs with hallways which there isnt much more than 3' of ceiling space and returns smack dab in the middle so there are plenty of circumstances which make staying clear of either is next to impossible