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Duct Smoke Detectors
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Re: Duct Smoke Detectors By  lockek

Posts: 0

3/4/2008 4:55:00 AM

The issue with the 5 ton thing is that not all manufacturers 5 ton AHU/FC produce 2000 cfm. For years Goodman/Janitrol''s 5 ton AHU/FC only produced 1800 cfm with no static pressures.

The main difference between the IMC and the NFPA 90A is in the wording of when the detector is required. The IMC states, "where the DESIGN capacity is GREATER than 2000 cfm". Whereas the the NFPA 90A states where "the CAPACITY is GREATER than 2000 cfm". The IMC defers to the actual design performance of the system where the NFPA seems to be more concerned with the unit''s actual maximum ability. However, in either case, the requirement is not for a 5 ton air handler, but an air handler which either is designed or has the ability to produce MORE than 2000 cfm. So not all 5 ton AHU''s would require a duct detector.

If a certified test and balance report indiated a unit was operating at 2000 cfm or less then what language would an inspector have to require a duct smoke detector to be installed? Additionally, if the manufacturer''s fan curve chart showed there was no way the unit could produce greater than 2000 cfm, how could the inspectors require the detectors.

The agreement I have with our Fire Inspectors is if the unit has the ability to exceed 2000 cfm, we will both require the detector, but under the threshold, neither will require the detector.


Re: Duct Smoke Detectors By  doughill3

Posts: 0

3/4/2008 4:57:00 AM

More thanks.

My interpretation of "design capacity" is the system as designed, stamped, sealed by the Mechanical Engineer. Equipment capacity is important to the designer but not relevant post-design.
I have flexible duct rated to 5000 CFM, and this does not mean my design capacity is 5000 CFM.


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