Insulating around double walled chimney

[ozzy73]

I would like to insulate with 2" Celfort and frame around the double walled chimney.

Would you recommend using some sort flashing to keep heat away from the XPS, framing and the ABS pipe ?

What are code requirement for framing around double walled chimney ?


Thx.

Ozzy

 

[SlyFerret]

I'm assuming that you're referring to the double walled class-A chimney pipe, not the double wall black stove connector pipe.

The double walled class-A pipe that I used requires 2" of airspace to combustibles. This just came up in another thread. That airspace requirement is intended to be airspace, not insulation, so make sure that you have proper clearances.

-SF

 

[ozzy73]

SlyFerret

Yes I am refering to the cass-A chimney pipe. I will maintain a 2" airspace to combustibles.

Does this mean I can not place high temp drywall right up the chimney ?

The concrete patch around the pipe seems to be flaky and cracked. Is there a recommended "high temp" patch kit I should be using for this ?

Ozzy.

 

[Metal]

Type 103HT (Class A) pipe's 2" Clearance to Combustibles is "Clearance to Combustibles." You can put anything in that 2" space as long as it is not classified as a combustible material.

 

[SlyFerret]

Im not familiar with high temp drywall. If you are referring to Durock or some type of cement board, I don't believe that those are considered combustibles.

-SF

 

[Metal]

If it is a paperless drywall you will be okay as the paper backing is what makes drywall a combustible, if it is papered it needs to meet the 2" CTC.

 

[webbie]

Type 103HT (Class A) pipe's 2" Clearance to Combustibles is "Clearance to Combustibles." You can put anything in that 2" space as long as it is not classified as a combustible material.

Could you elaborate on that?
I can understand where it would not apply in a horizontal situation like this, but I always assumed that having air around it allowed heat to "run up and off" the chimney pipe.

Are you saying, for instance, that a straight up chimney could have rock wood around it for 2" where it passed through ceiling and floors?

 

[webbie]

I would like to insulate with 2" Celfort and frame around the double walled chimney

Would you recommend using some sort flashing to keep heat away from the XPS, framing and the ABS pipe ?

What are code requirement for framing around double walled chimney ?


Thx.

Ozzy

Ozzy, let me answer the question as best I can.

When you use insulated pipe as a "crock" through a wall with combustibles (which the joists, band and pipe insulation are), they the code specifies much more than 2" clearance. Your situation looks somewhat in-between....not exactly sure from the pic exactly what happens after the wall (is chimney insulated all the way up, or is this used to enter a masonry chimney?)

Anyway, without looking up all the NFPA stuff - which probably does not exactly address this anyway, I would guess that a wrapping of even 1" or insulation and then some aluminum or light sheet metal around that (just to hold it all together) should make the job quite safe. I am only addressing the insulated portion, not the black.

Wrapping flashing around the pipe insulation itself would also be great, especially if the one wrap (the HT 103 pipe) does not touch the other (the smaller pipe above)

 

[ozzy73]

The insulated pipe exitst the foundation and goes straight up the exterior of the house.

The pipe above it is 3" ABS discharge line to our Septic system, I defenetly do not want to burn through that. :ahhh:

I will plan for 3" to 4" ( max between abs and chimney ) clearance around the chimney and also wrap some flashing around the wall insulation, studs and the pipe itself.

Ozzy

 

[jtp10181]

Type 103HT (Class A) pipe's 2" Clearance to Combustibles is "Clearance to Combustibles." You can put anything in that 2" space as long as it is not classified as a combustible material.

Most pipe clearances listed are AIR SPACE clearances. What you are saying means one could wrap an entire Class A HT system in 2" of kaowool and then have paper wrapped around that. Doesn't sound safe to me, the pipe would overheat from all the insulation and probably start the paper on fire eventually. You can't say that's excessive because there is no in between, its either an air space clearance or its not. You can't say non-combustibles can be in that zone within reason because one persons reason might be different that another.

The ONLY except to the air space is wall penetrations where appropriate thimbles or fire stops are used.

Read this Simpson install manual.

(broken link removed to http://duravent.com/docs/instruct/L150%20Dec05.pdf)

Quoted: Maintain at least a 2-inch air space between the outer wall of the chimney and the enclosure

They mention air space clearances in a few place including the opening statement in giant bold lettering

A MAJOR CAUSE OF CHIMNEY RELATED FIRES IS FAILURE
TO MAINTAIN REQUIRED CLEARANCES (AIR SPACES) TO
COMBUSTIBLE MATERIALS. IT IS OF THE UTMOST IMPORTANCE
THAT THIS CHIMNEY BE INSTALLED ONLY IN
ACCORDANCE WITH THESE INSTRUCTIONS.

Found one more good quote

Never fill any required clearance space with insulation or any other materials.

 

[ozzy73]

Thank you all for your suggestions. Unfortunately I only have 2 1/2" of clearance above the chimney.

I will rig something up with flashing and provide an updated pic next week.

Ozzy.

 

[webbie]

ozzy, I think you will be OK - we are addressing entire vertical chimney systems where this insulation may be used against the pipe. Yours is "in the field" and very visible to you, and I think you will be OK with your ideas.

 

[jtp10181]

What is the point of all this anyway? Are you trying to deflect heat away from the septic line?

 

[ozzy73]

It took quite some time but we did complete the installation.
I wanted to update the thread with some pictures on how the framing and insulating was done along with a bulkhead to hide the 3' ABS Septic pipe. We did have help from a local wett certified professional for the chimney.

Elmira Wood Stove - 900 cleaned and painted.
New Super Vent Chimney from T up, old chimney was rusted out.

Framing and Insulation -- (broken link removed to http://picasaweb.google.com/rzvarga/Chimney#)

Chimney and Stove -- (broken link removed to http://picasaweb.google.com/rzvarga/ElmiraStoveWorks?authkey=dS4rA7gyeoU#)

Comments and suggestions are welcome.

Ozzy