# smoke alarms and cold air returns



## bptp32

2010 Residnetial Code of NYS based on 2006 IRC:  A question has come up regarding the placement of smoke alarms and the location in regards to cold air returns.  According to NFPA 72 "(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."  Would this apply to cold air returns as well.  We very seldom see heat registers near the top of the wall ceiling intersection where the smoke alarms are located.  Some of the installation manuals state 3' from a supply or cold air register.  We are having a general discussion on whether this distance separation would apply to cold air registers also.  Thansk for the help.


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## Gregg Harris

bptp32 said:
			
		

> 2010 Residnetial Code of NYS based on 2006 IRC:  A question has come up regarding the placement of smoke alarms and the location in regards to cold air returns.  According to NFPA 72 "(6) Smoke alarms and smoke detectors shall not be installed within a 914 mm (36 in.) horizontal path from the supplyregisters of a forced air heating or cooling system and shall be installed outside of the direct airflow from those
> 
> registers."  Would this apply to cold air returns as well.  We very seldom see heat registers near the top of the wall ceiling intersection where the smoke alarms are located.  Some of the installation manuals state 3' from a supply or cold air register.  We are having a general discussion on whether this distance separation would apply to cold air registers also.  Thansk for the help.


I do not have a copy of NFPA 72, but if the verbiage that you typed is correct it makes sense. Apropperly designed HVAC system is going to have a supply velocity of around 900 feet per minute and would blow the smoke away from the detector until the supply air gets laden with smoke. The return air should have a velocity around 300 to 400 feet per minute and would pull the air and concentrating the smoke from the space across the detector to cause it to alarm.


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## BSSTG

Greetings

Well this post got me to thinking I have not looked at those requirements in a long, long time. And I can't find in my 2010 NFPA 72 any reference to location adjacent to air registers. I have found references to distance from cooking equipement and bath doors and for locations of detectors in odd structured bldgs. I will add that there is a whole lot to read in this and maybe I'm just missing it. It's got really fine print!

If someone has an exact reference I would be interested in it. I had thought that the IRC made reference to air registers too but I can't find that either.

BS


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## BSSTG

Well I goofed,

Sure enough I found it just moments after typing the above post..

2010 NFPA 72 A.17.7.4.1

"Detectors should not be located in a direct airflow or closer thatn 36" from an air supply diffuser or return air opening." ..It goes on to say that this only a minimum.

I too had though that the return air opening requirment had been removed. I'm glad this came up.

BS


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## bptp32

"(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."

Here is a copy out of the 2007 NFPA whcih is the most current version adopted by the State of NY.  Hope this helps


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## Gregg Harris

So it looks like 2010 they added the "return air grill"??


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## LGreene

I just saw something about this on a health care life safety blog the other day.  Here's a link in case it's helpful to anyone:

http://keyeslifesafety.com/spot-type-smoke-detectors-used-in-air-flow/


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## BSSTG

Gregg Harris said:
			
		

> So it looks like 2010 they added the "return air grill"??


 This is in the annex. So it is explanatory material. The actuaL reference reads thusly. NFPA 72 (2010) 17.7.4.1

'In spaces served by air-handling systems, detectors shall not be located where airflow prevents operation of the detectors."

I don't have access to older versions. In the 2010 it does not indicate any change to this section.

BS


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## peach

supply air dilutes the smoke; return air will pull the smoke past the detector.

The manufacturer's literature tells you exactly where not to put the smoke detector.  Need to stay away from fan blades too.


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## ICE

As air moves across a flat surface a zone of reduced air pressure is created at the surface.  The faster the air movement, the greater the drop in air pressure.  That's why airplanes are able to fly and may be why smoke detectors should not be located in an air-stream.

Detectors located inside duct must be different from those on a ceiling.

Another location to avoid is at corners where the wall and ceiling meet.  The detector should be a minimum of four inches from the corner.


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## jame

home alarm Brisbane


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