# Single wall vent {PIC}



## ICE (Aug 27, 2011)

Would you allow either of these?

The single wall stops a few inches into the Transite.







The single wall is through the Transite and above the roof.


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## Msradell (Aug 27, 2011)

Don't really like either one of them but in reality I really don't see any major problems with the second one of them possible rain leakage.  The first one appears to have a large potential for fume leakage back into the building through the joint.


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## pete_t (Aug 28, 2011)

*2010 CALIFORNIA MECHANICAL CODE*

Not sure about the occupancy in Picture 1.

Picture 1

*802.7.4 Installation with Appliances Permitted by*

*Section 802.4.1*.

*802.7.4.1 Prohibited Use*. Single-wall metal pipe

shall not be used as a vent in dwellings and residential

occupancies. [NFPA 54-09:12.8.4.1]

*802.7.4.2* Single-wall metal pipe shall be used only

for runs *directly from the space in which the appli-*

*ance is located* through the roof or exterior wall to

the outer air. A pipe passing through a roof shall

extend without interruption through the roof

flashing, roof jacket, or roof thimble. [NFPA

54: 12.8.4.1]

And

TABLE 8-2

CLEARANCE FOR CONNECTORS

[NFPA 54: TABLE 12.8.4.4]

(6 in clearance required to the insulation)

Picture 2

802. 7 Single-Wall Metal Pipe[/b].

802.7.1 Construction. Single-wall metal pipe shall be

constructed of *galvanized sheet* steel not less than 0.0304

inch (0.7 mm) thick or of other approved, noncombustible,

corrosion-resistant material. [NFPA 54: 12.8.1]


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## mark handler (Aug 28, 2011)

Both pictures are very common in houses built in the late forties and early fifties.


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## Pcinspector1 (Aug 30, 2011)

We see 26 gauge metal protecting the rafter or double wall with the 1" clearance here most of the time.

Is Transite (abestos) still allowed by code if left alone?

pc1


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## ICE (Aug 31, 2011)

Transite can be left in place and metal vent can pass through it.  The FAU installation instructions that I have read will not allow it to be used as a vent because it doesn't heat up and facilitate a draft the same as steel vent.  Additionally, induced draft vented appliances require a tighter seal than Transite provides.  Poorly sealed gravity vent may not be an issue as the leak allows cold air to enter the vent much the same as a draft hood and facilitates the draft.

Water heater installation instructions that I have encountered do not have the same prohibition.  I have allowed the reuse of Transite as a vent for water heaters if the Transite is continuous and in good condition.  I can see that as a problem as water heaters become more efficient and less heat is released through the vent, which hinders the action of a gravity vent because it take longer to heat the vent.

Wall heater installation instructions are not as clear when it comes to the vents but I have spoken to several manufacturers and have been told that they won't allow the reuse of Transite or even an old metal vent.  They want new BW vent in the stud cavity and new B vent in the attic.

Admittedly, my knowledge on the subject is limited and I would appreciate hearing from anyone that knows more.

Pete_t mentions a table from the CA Mechanical code and states that single wall vent clearance to combustibles is 6".  I haven't looked it up but as I recall, 6" clearance is allowed only outside a building and 18" clearance is required inside a building.


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## pwood (Aug 31, 2011)

ice,

 table 8-2 cmc, basic stuff


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## ICE (Aug 31, 2011)

pwood said:
			
		

> ice, table 8-2 cmc, basic stuff


Thanks,

I don't know why I thought there was a difference between outside and inside clearances unless the code used to say that and has changed.  Anyway, I need to change.


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