Duct Detector placement

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JAbrahams5

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Master Electrician / Project Engineer
I have a question for the Fire Alarm Gurus / NICET certification holders. I am currently on a project where there are quite a few Duct detectors indicated on ducts where there is no way to install the housing at the locations prescribed by the manufacturer's installation instructions. There is just not enough duct. I have heard muttering and statements that in this situation, as close to meeting the criteria as possible will suffice. I am not able to make this determination from NFPA 72, nor am I an expert on airflow. this issue was brought up to me by the mechanical contractor asking how to proceed. Surely this cannot be the only time that this issue has come up on a project. Does anyone have any input on how this situation has been successfully remedied?
 
Well, my NICET Level 2 certification has expired and I'm just a fire alarm guy. That said, if you are using an EST fire alarm panel a SIGA-OSD smoke detector installed inside the duct using their DMP (duct mounting plate) might fit. Don't install it on the bottom of the duct.
 
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Presuming you're talking about the thermostat, I have installed several dozen or more, and they were allowed to be in the hood if there was no access to the duct, as long as they're above the grease catchers.
 
LarryFine said:
Presuming you're talking about the thermostat, I have installed several dozen or more, and they were allowed to be in the hood if there was no access to the duct, as long as they're above the grease catchers.
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These are duct detectors in the general HVAC system, not the "finger" detectors a kitchen hood exhaust system.
 
JAbrahams5 said:
I have a question for the Fire Alarm Gurus / NICET certification holders. I am currently on a project where there are quite a few Duct detectors indicated on ducts where there is no way to install the housing at the locations prescribed by the manufacturer's installation instructions. There is just not enough duct. I have heard muttering and statements that in this situation, as close to meeting the criteria as possible will suffice. I am not able to make this determination from NFPA 72, nor am I an expert on airflow. this issue was brought up to me by the mechanical contractor asking how to proceed. Surely this cannot be the only time that this issue has come up on a project. Does anyone have any input on how this situation has been successfully remedied?
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The situation can't be remedied without taking the HVAC designers out and shooting them wholesale. 😁 Barring that, just do the best you can. The return and supply (if needed) detectors need to be after all return feed ins and before any exhaust outlet or fresh air inlet for the former, and before the first branch line for the later. They do not have to be within any specified distance from the air handler, specs and local amendments notwithstanding, so you might have more options than you think.
 
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