# Type I Hood Make Up Air Duct Material



## Glennman CBO (Sep 8, 2015)

2012 IMC. Designer is proposing to install flammable flexible air duct material for make up air at a Type I hood. This will ultimately be directly connected to the hood.

The plans show a 24" section of "start up" steel duct, then the flexible duct connects to that so that the flammable duct will end up 18" away from the hood, per 506.3.1.2, at all points.

The code is not completely clear where it states ducts "connecting within" 18" of the hood shall be non-combustible. Does "connecting within" mean "connecting to" ?

Thanks to all in advance.


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## Sifu (Sep 8, 2015)

I would need to check but as far as I know there is no exception for clearance to combustibles from the hood so if the combustible duct doesn't transition to the steel outside of the 18" minimum I would say no dice.


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## mtlogcabin (Sep 9, 2015)

506.3.1.2 Makeup air ducts.

Makeup air ducts connecting to or within 18 inches (457 mm) of a Type I hood shall be constructed and installed in accordance with Sections 603.1, 603.3, 603.4, 603.9, 603.10 and 603.12. Duct insulation installed within 18 inches (457 mm) of a Type I hood shall be noncombustible or shall be listed for the application.

Flexible duct is not included in the above sections. After the 18 inches I see no prohibition for using flex duct.


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## Glennman CBO (Sep 9, 2015)

Thank you. This appears to go along with the intent of the code. I see no reason why the duct would need to remain non-combustible after the 18" since there is no longer a requirement for clearances after 18" either. It wouldn't make sense to require all non-combustible duct, but then not have any clearance requirements outside of the first 18" section.


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## JBI (Sep 10, 2015)

If there is a fire in the hood or it's exhaust duct, the worst that can happen is that the make-up air flex duct becomes compromised and that duct no longer is capable of supplying make-up air to a fire in progress.

Am I missing something?


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## mtlogcabin (Sep 10, 2015)

JBI said:
			
		

> Am I missing something?


[F] 904.3.3 System interlocking.

Automatic equipment interlocks with fuel shutoffs, ventilation controls, door closers, window shutters, conveyor openings, smoke and heat vents and other features necessary for proper operation of the fire-extinguishing system shall be provided as required by the design and installation standard utilized for the hazard.


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