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» ICC Bulletin Board » Code Chat » Plumbing, Mechanical and Fuel Gas Codes » Grease Duct Enclosures

   
Author Topic: Grease Duct Enclosures
wlk404
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Gentleman,

What is your (collective) opinion on the use of gypsum products used for a Type 1 grease exhaust duct enclosure?

The Mechanical Code (508.4) requires a rated shaft but the gypsum board installation instructions and 602.1 limits exposure to temperatures in excess of 125 degrees for extended periods of time.

I have been told that the insides of grease ducts reach temperatures of 400-500 degrees for extended periods.

Any insights or comments would be appreciated.

Posts: 41 | From: ca | Registered: Jun 2006  |  IP: Logged
cda
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no problem

done all the time, have not seen any fires because of the sheet rock failure.

not sure howe hot a grease duct gets during extended use but with a good ventaltion system seems like the only time it would get very hot is when it is on fire.

maybe give this guy a call

http://www.philackland.com/

Posts: 6255 | From: Had to move to parent's basement without code compliant escape window | Registered: Oct 2000  |  IP: Logged
Grey Areas
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The shaft protection for grease ducts has been in the code's for years. Is a field constructed shaft built out of drywall, tested and listed specifically as a grease duct enclosure ? Good question. Will the allowance for a field constructed shaft stay in the codes. Now that there are lised tested methods ?
Posts: 37 | From: South Idaho | Registered: Mar 2005  |  IP: Logged
wlk404
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The reason this question was asked was because our local 3M representative (yes, the salesperson) mentioned to us that technically, gyp board was not designed to be used for grease duct shafts. Of course, they suggested that 3M firebarrier was a superior product for that use.

Concerning the 3M firewrap, does any other jurisdiction require the wrap to be installed on the duct from the roof to the penetration of the ceiling, even if there is no combustibles within 18 inches of the duct.

Also, it seems justifiable that the top of the hood get the same protection when the installation extends the hood above the ceiling, or when the ceiling does not continue to the firewrap, since the hood and the duct are part of one assembly.

Any comments would be appreciated.

Posts: 41 | From: ca | Registered: Jun 2006  |  IP: Logged
cda
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yes yes and no

the problem is getting a true u/l one hour shaft.

Posts: 6255 | From: Had to move to parent's basement without code compliant escape window | Registered: Oct 2000  |  IP: Logged
Builder bob
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same as cda, the 3M wrap is usually used in lieu of a one hour rated shaft.

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Can you build to minimum standards? FWIW - MCP, CBO, CPE, CI, CFPE, ASCET
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Posts: 4199 | From: Lost in the South........ | Registered: Apr 2004  |  IP: Logged
Dr. J
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I agree with the 3M rep (after filtering for sales crap). Gyp board would fail the tests used in the listing of the wrap products. However, gyp board enclosures are in the code, and therefore are still legal.

The wrap products serve two functions - combustible clearance reduction and as a rated enclosure. Make sure the product is being installed in accordance with the listing for the specific function.

Per IMC 506.3.10 "A duct enclosure shall not be required for a grease duct that penetrates only a nonfire-resistance-rated roof/ceiling assembly." This would be the case for many single story buildings.

Posts: 516 | From: Colorado (Denver area) | Registered: Mar 2005  |  IP: Logged
wlk404
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Agreed. Enclosures constructed as required for fire-rated shafts are provided for in the Code.

The 2006 UMC has new language that seems to indicate that shafts (or enclosures) would not need to be installed in single story, non rated buildings. The 2006 CMC, however, added revised language for occupancies under the jurisdiction of the State Fire Marshall (SFM) to have shafts or enclosures regardless of number of stories or fire rating, if I am reading that right.

It seems that the IMC and the UMC have similar requirements, with different verbiage, and with the California Mechanical Code, it seems to indicate that the shaft or enclosure requirement for single story non-rated buildings comes back.

At least that is the way I interpret this information.

Thanks for all your comments.

Posts: 41 | From: ca | Registered: Jun 2006  |  IP: Logged
A Picker
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WLK, as I understand it, the shafts are tested as UL assemblies. The wraps, firemaster or pyroscat do work very well from stoping the heat inside of a grease duct that has a fire inside from getting to the surrounding construction. We have had a few fires in our area where the exhaust ducts were wrapped that stopped the fire from spreading and burning the building. We also have had buildings burn from using the old chicken wire and mineral wool method. I encourage anyone to wrap their duct as opposed to a shaft for that reason... If the wrap is in an area that cannot be damaged or picked off, then even the wrap needs protected.
Posts: 270 | From: Greenville SC | Registered: Jul 2005  |  IP: Logged
falco
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Does anybody require the exposed grease duct below the ceiling to be firewrapped?

I have an installation where the hood is mounted about 5 feet below the ceiling. The grease duct runs horizontal about 10 feet and then up through the ceiling and through the roof.

I think the section below the ceiling does not need to be firewrapped, just from the "point of penetration" at the ceiling and up through the roof?

Does anybody disagree?

Posts: 25 | From: ca | Registered: Jun 2006  |  IP: Logged
Builder bob
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Firewrap would be required where:
a fire rated shaft would be required or
Where the Hood Ductwork gets within 18" of combustible materials.

This includes wiring, electrical conduit, PVC pipes, etc.
The 2003 IMC does not recognize limited combustible materials like NFPA 96 does.

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Can you build to minimum standards? FWIW - MCP, CBO, CPE, CI, CFPE, ASCET
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Posts: 4199 | From: Lost in the South........ | Registered: Apr 2004  |  IP: Logged
   

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