# Duct smoke detector



## BBQ (Nov 16, 2010)

darren79 said:


> I have a duct smoke detector to install. I have the smoke detector and a 5' section of sampling tube. Do you just cut the tube to fit the duct or is there more to it.


Yes, there is a lot to it if you want it done right.

I know this is a shocking suggestion but read the directions. :thumbsup:


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## MechanicalDVR (Dec 29, 2007)

How many CFM is the unit? If it's over 2000 CFM you may need supply and return detectors. But most important, read and follow instructions.


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## Chris Kennedy (Nov 19, 2007)

Have a licensed mechanical contractor install the duct detector, you put power to it and have a licensed F/A contractor connect it to the system.


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## BBQ (Nov 16, 2010)

Chris Kennedy said:


> Have a licensed mechanical contractor install the duct detector, you put power to it and have a licensed F/A contractor connect it to the system.


We do it all.


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## darren79 (Dec 20, 2011)

BBQ said:


> Yes, there is a lot to it if you want it done right.
> 
> I know this is a shocking suggestion but read the directions. :thumbsup:



I did read them, one part says to stick the unused tube out the other side of the duct but there is not enough room to stick it out the other side. One part says if you cut it you have to make more holes in it. 

I was trying to see what everyone else done with them.

It also says that you can put a second tube in(exhaust maybe) but that is optional.


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## darren79 (Dec 20, 2011)

Chris Kennedy said:


> Have a licensed mechanical contractor install the duct detector, you put power to it and have a licensed F/A contractor connect it to the system.



If I did that I would have nothing to do since there is no power run to smoke detector.


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## drsparky (Nov 13, 2008)

After you read and heed the directions then plug in a manometer to read and record the differential air pressure. It will probably be around 1.4 inches of water. The liability involved with fire alarm work requires doing it by the book.


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## wildleg (Apr 12, 2009)

darren79 said:


> If I did that I would have nothing to do since there is no power run to smoke detector.


I'm pretty sure I've installed some that had 120v power, but it was a while back.


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## 360max (Jun 10, 2011)

...because of the duct width, you need to send the pipe through the entire duct so the sampling tube (pipe) can be supported, the instructions probably state this. The instructions also state the holes in the sampling tube (pipe) should face 'into' the airflow so the air flows into duct detector.


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## 360max (Jun 10, 2011)

wildleg said:


> I'm pretty sure I've installed some that had 120v power, but it was a while back.


most are low voltage these days, but I'm sure they still have the line voltage ones.


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## manchestersparky (Mar 25, 2007)

cut the sampling tube about an inch or two longer than the duct width your installing it in. Let the excess tube stick out the opposite side of the duct. Be sure to install the rubber "stopper into the sample tube and to seal around the tube where it exits the duct on the opposite side.

The tube is basically supported by the duct detector on one side and the duct work on the opposite side.
I've installed hundreds of them myself and have wired hundreds more that others have installed the same exact way as I described.


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