duct board; combustible material?

[brianmiller]

What's your all's take on duct board as combustible material?

The local AHJ allows furnace vents to contact duct board material in order to provide a barrier/prevent the vent to contact "combustible material", such as sheetrock, refrigernat line insulation, etc?

I think duct board is combustible material so I don't get why the AHJ would allow this exception.

You all agree with the AHJ?

Brian

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[Jerry Peck]

Does not matter whether it is, or is not, combustible as the Type B Gas Vent is not allowed to touch insulation either, which is what duct board is. Requires the same 1" air space to insulation as to combustible material.

[Billy Stephens]

.
]Does not matter whether it is, or is not, combustible as the Type B Gas Vent is not allowed to touch insulation either, which is what duct board is. Requires the same 1" air space to insulation as to combustible material.

.
What does NFPA 90 A & B say ? Ultra*Duct™ Black Duct Board - HVAC-Mechanical - Insulation - CertainTeed See Technical Information on link.

[H.G. Watson, Sr.]

.
What does NFPA 90 A & B say ? Ultra*Duct™ Black Duct Board - HVAC-Mechanical - Insulation - CertainTeed See Technical Information on link.

Does not matter whether it is, or is not, combustible as the Type B Gas Vent is not allowed to touch insulation either, which is what duct board is. The B-vent (sic) Requires the same 1" air space to insulation as to combustible material.

BS, The answer was in what you quoted. I added the implied subject and highlighted for clarity.

[brianmiller]

Thanks, Jerry, HG...

How would you present a case to convince the stubborn AHJ that type-b vents should have a 1" clearance from duct board.....I already tried saying that it is insulation...he cited the NFPA section that Billy provided as his counter arguement.

[Jerry Peck]

How would you present a case to convince the stubborn AHJ that type-b vents should have a 1" clearance from duct board.....I already tried saying that it is insulation...he cited the NFPA section that Billy provided as his counter arguement.

G2427.6.1 (503.6.1) Installation, general.

Gas vents shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.

Then pull out the manufacturer's installation instructions which says that there must be 1" clearance to combustible material AND "insulation". To my knowledge, and Bob Harper has more information on this than I do, they will all state "and insulation".

[H.G. Watson, Sr.]

brianmiller,

Although you didn't indicate (unless I missed it), and assuming you're referring to a gas-fired furnace; I would refer them not to NFPA 90 A & B which has to do with conditioned air distribution, ducting & A/C, etc.; but regards to the VENTing, to NFPA 54 which is equal and a.k.a. the ANSI standard refered to in the literature for the furnace appliance and the vent material manufacturer, or to the IFGC which may also be refered to by the aforemented manufacturers in their instructions, which covers the exhausting/venting of fuel gas fired appliances - i.e. the furnace itself, and covers clearance, length, offsets, diameter, elevation, support, drafting, requirements for both B-vent and single wall vent (greater clearances) & vent connectors (greater clearances). It is not only combustion/carbonization of combustibles that is being avoided, but avoiding "hot spots" & "cold spots" for the venting material and overall vent that must be avoided to assure proper draft and complete exhaust/venting of the products of combustion.

It is the restrictions and required clearances for for the vent (think chimney) that rule here not those for the ducts/distribution/conditioned and return air handling system and materials accomplishing same.

As JP indicated manufacturer's listed instructions, the listing itself of the vent material itself also "rule" in this matter; as would the manufacturer's listed instructions for the furnace itself.

If the furnace is solid fuel or fuel oil fired, obivously the fuel GAS codes wouldn't apply, but others would. If the furnace is an electric one, obviously there wouldn't be a vent for the furance itself, per se. An HRV, or other fresh air ventillation system perhaps but not a "products of combustion" exhaust vent/chimney. You might also refer to the mechanical sections of your local codes.

Regarding NFPA 90B, you can defer to

5.1.1.2 Where an appliance, ductwork, or a chimney or vent connection is listed for different clearances, the listed clearances shall apply.

and

Table 5.1.2.1 "Clearances to Combustible Material for Furances, Boilers, Solar Engergy Heating Devices, and Heat Exchangers Installed in Rooms That are Large in Comparison with Size of Appliance" : Columns entitled "Projecting Flue Box or Draft Hood" and "Chimney or Vent Connector" under "Minimum Clearance"

and

Table 5.1.4.2 "Reduction of Clearances with Specified Forms of Protection"

as applicable.

HTH.

[Bob Harper]

B-vent is a listed product so you must follow the listed instructions, which require a 1" clearance. This is not only to combustibles but to maintain an air space to cool the vent. If you fill the stated clearance with anything such as concrete, Superman's cape or this stuff, you defect the primary cooling system of the vent and void the warranty and listing, which in and of itself is a code violation.

This product carries an ASTM E-84 flame spread rating of 25, which is echoed by its UL 181 listing (same requirement). This means it burns 25% as fast as red oak in a 25 ft Steiner Tunnel test--------but it still burns! Therefore, it by definition IS combustible. Moreover, I did not see an ASTM E-136 rating, which is THE std. for materials to be rated as non-combustible so this particular material fails two ways right there. NFPA 90 just means it is recognized for certain ducts--not as a recognized combustion vent material.

BTW, this stuff is not listed in NFPA 211 as an acceptable clearance reduction material, which btw, must be non-combustible. While your AHJ is in NFPA 211, ask him to read the definition of noncombustible. It's also reflected in NFPA 97.

Now, back to the listing. When you penetrate walls and ceilings, regardless of their construction* you SHALL use a listed firestop-period. This stuff is not a listed firestop, therefore cannot be used as such. Moreover, according to the IRC 303.111, this stuff is not listed as one of the acceptable materials for fireblocking around a listed firestop. Therefore, you AHJ would have to rule on its acceptability for such use but only as fireblocking around a listed firestop. He does not have the power to overule a listing. Moreover, in order to approve this stuff for use as fireblocking, he would have to demonstrate this material, in the form and method installed can, a) provide an "effective barrier", and b) remain in place under the conditions of use anticipated. That means somebody has to figure out how you are going to support this stuff mechanically and secure it in place.

Therefore, this stuff or any other unlisted building material cannot substitute for a listed firestop or other listed component.

On a practical note, this stuff will stink and can end up in litigation when a homeowner traces their runny nose, scratchy throat, mood swings, decreased libido, etc. to this stuff off-gassing. Since you cannot sue your AHJ, the contractor will be left holding the bag.

Now, back to my * above where I said "regardless of construction". I'm referring here to residential construction under the 2009 IRC. If your buiding is 4 stories or more, your chimney "chase" just became a "shaft", which must be fire rated based upon the occupancy. Note very, very few listed firestops are also listed to UL 814 for fire rated firestops. Here is where a design professional (read--someone other than your AHJ who actually understands firestopping) can design a commercial firestop *assembly*, which in this case, would require communication with the mfr. of the vent on approved methods that void the listing.

How's that for my short answer?