Asbestos concrete chimney

[Bluto]

Hello, complete newbie, but have been reading a lot.

I want to install a wood burning stove in the basement of my 1200 sq ft ranch home. I have an existing asbestos concrete chimney near where I plan to install the stove (right next to the furnace). The previous owner used it to vent the water heater, but I went with an electric heater.

The asbestos concrete is in good condition, no deterioration, and is 8" wide and at least 17' long. Can I use this to vent my stove, or should I still install a liner? I'm betting that you'll advise me to use a liner as there may be cracks now, or eventually?

Also, I wasn't planning on adding a blower, but I may be wrong. The stove will be near the middle of the basement, and will lie under the main supply branch of my Hvac system, and a few feet from a cold air return that immediately feeds into the furnace. The basement will have a few rooms, which I will feed with new ducting I will install. The stove goes in the larger part of the basement that is near an open staircase to the living room/kitchen. I don't intend for the stove to warm the entire home, but hoped to supplement the furnace.

The house is well insulated and early evidence suggests it will be harder to cool than to heat due to window size and placement.

Any recommendations would be appreciated.

 

[bcrtops]

There are 2 main issues here:

1) Unlined masonry chimney -- almost all current state/local codes will require a liner on a new installation. There are good reasons for this -- the main one being keeping the chimney warm/hot & prevent creosote buildup.

2) Air intact near a free-standing stove is a bad idea. In a recent thread, it was mentioned that an intact air vent had to be at least 10' away from a wood stove in WA state. Check local codes. Without going into detail, there are numerous reasons for this.

(I could write an essay on the why, etc. of the above. Codes have changed immensely since the 70's & 80's -- what was thought to be OK & great back then is likely not so today. All to do with fire danger -- the newer codes, etc.)

 

[Bluto]

There are 2 main issues here:

1) Unlined masonry chimney -- almost all current state/local codes will require a liner on a new installation. There are good reasons for this -- the main one being keeping the chimney warm/hot & prevent creosote buildup.

2) Air intact near a free-standing stove is a bad idea. In a recent thread, it was mentioned that an intact air vent had to be at least 10' away from a wood stove in WA state. Check local codes. Without going into detail, there are numerous reasons for this.

(I could write an essay on the why, etc. of the above. Codes have changed immensely since the 70's & 80's -- what was thought to be OK & great back then is likely not so today. All to do with fire danger -- the newer codes, etc.)

Thanks for replying. I can think of reasons for not having a return too close. I haven't begun finishing the basement yet, so fortunately I will change my plans for a return at the furnace.

 

[bholler]

Can you post a pic of your chimney? I have seen several different types of asbestos chimneys. But for wood I would think almost all of them would need lined. From what I have seen the inner wall of most are somewhat porous

 

[Bluto]

Sorry about the delay posting. The first pic is the 8" asbestos concrete pipe that extends from my basement through the roof. I would like to use this along with a liner to vent my wood stove.

The second shot shows the placement where I would like to put the stove. The potential obstacles are above in the photo, a structural beam, a gas line tucked up close to the joists and a supply branch of the hvac system. The hvac hangs at 70", the beam at 72", the gas line at 83".

The third shot shows the current hot water tank venting into the concrete pipe; this is the same way I want to vent the stove.

I want to put the stove under the beam. How well should I isolate the stove from the beam/gas line? I was thinking I could create a thermal mass, sloped away from those obstacles towards the living area of the basement, with insulation between the mass and beam/ gas line. I was planning to add mass to the surrounding area anyway. The structure can support the added weight of the mass barrier.

Thought are appreciated.

 

[bholler]

I would like to use this along with a liner to vent my wood stove.

Nope there is no liner approved for use with a wood stove in that type of chimney. They all require a minimum 4" nominal of masonry around them

 

[Bluto]

Nope there is no liner approved for use with a wood stove in that type of chimney. They all require a minimum 4" nominal of masonry around them

Well if this is true, and I trust that you correct, I guess I'll have to scrap the plan. Is this requirement due to excessive heat transfer from the chimney into the structure?

 

[bholler]

Well if this is true, and I trust that you correct, I guess I'll have to scrap the plan. Is this requirement due to excessive heat transfer from the chimney into the structure?

Yes It may be fine but there are no liners that have been tested for that application and because of thet it will never meet code requirements.

 

[Bluto]

Yes It may be fine but there are no liners that have been tested for that application and because of thet it will never meet code requirements.

This means I'll have to move the stove to one end of my home, instead of dead center of the basement next to my hvac. Disappointed. I felt I was safe with this much mass. Or the other option of a footer and masonry.... I have the space, but nope...

 

[nola mike]

Is that chimney double walled? And is there a max horizontal run? Most that I've seen are pretty minimal lengths...

 

[bholler]

This means I'll have to move the stove to one end of my home, instead of dead center of the basement next to my hvac. Disappointed. I felt I was safe with this much mass. Or the other option of a footer and masonry.... I have the space, but nope...

You could always just replace it with a class a stainless chimney.

 

[Bluto]

You could always just replace it with a class a stainless chimney.

Could I do this without removing the 8 inch wide & 17' long transite pipe? I would either need to do a lot of cutting into asbestos, or a crane. If I can just add a stainless chimney inside of it, then I'm happy.

 

[bholler]

Could I do this without removing the 8 inch wide & 17' long transite pipe? I would either need to do a lot of cutting into asbestos, or a crane. If I can just add a stainless chimney inside of it, then I'm happy.

I really doubt it would fit inside.

 

[begreen]

Mechanical code dictates that the stove needs to be at least 10ft away from the return intake. Maybe consider putting the stove on the main floor. You will get a lot more visual enjoyment from it and it puts the heat where it's needed.

 

[Bluto]

I really doubt it would fit inside.

Understood, but worth looking into. I don't want the headache removing it, and I have some time before I can start buying anything. I appreciate your guidance and will be looking at both options, moving it, and a stainless chimney.

 

[begreen]

Understood, but worth looking into. I don't want the headache removing it, and I have some time before I can start buying anything. I appreciate your guidance and will be looking at both options, moving it, and a stainless chimney.

A 6" stainless chimney pipe will be 8" diameter. Most need 2" clearance or a 12" clear hole to the roof. ICC Excel can be installed with 1" clearance I believe or 10" clear all the way.

 

[Bluto]

A 6" stainless chimney pipe will be 8" diameter. Most need 2" clearance or a 12" clear hole to the roof. ICC Excel can be installed with 1" clearance I believe or 10" clear all the way.

Thank you! Please correct me if I am wrong. You are telling me that, at best, I can have stainless with an inch gap to the sheetrock/stud assembly, but I can't run metal up through an 8" concrete pipe that cannot ignite. I will accept that this is code, and that will dictate my actions, but would like to understand the rationale that a barrier of that mass would not increase safety?

 

[bholler]

I can have stainless with an inch gap to the sheetrock/stud assembly,

stainless with a layer of insulation yes and most need 2"

but I can't run metal up through an 8" concrete pipe that cannot ignite.

the concrete may not ignite but it can transfer heat which could ignite adjacent materials. We dont know it has not been tested.

 

[begreen]

You might be able to run 5" chimney pipe up the pipe if truly 8" ID and straight as an arrow with no mortar joint ooze all the way up. But your stove will likely require 6" and that doesn't deal with the separation from the return if closer than 10ft.

 

[Bluto]

Thank you I understand that it might not be possible. The transite pipe is, except for the basement ceiling, at least two inches from any surface, except at the rood surface. I might be able to remove the transite and install metal into the same space. So I would have at least 2 inches between the new metal and a combustible surface?

 

[begreen]

Maybe? You know your house better than we do. There would need to be a ceiling support box at the basement ceiling level. Is there access from above to install that?

 

[Bluto]

Maybe? You know your house better than we do. There would need to be a ceiling support box at the basement ceiling level. Is there access from above to install that?

I appreciate your reply. I have access to the 8inch pipe at three locations; from the attic area I have several inches of clearance from the pipe to other structural elements. I can access the pipe through a main floor closet. The bottom of the pipe is where it enters my basement. I have access to the area above the basement access.

 

[begreen]

There would need to be a ceiling support box at the basement level and a firestop as it passes through the 1st floor ceiling to the attic, with an attic insulation shield on top of the firestop. The chimney will need to be boxed in a chase with 2" clearances as it passes through the first floor. Something like this.

 

[Bluto]

Thanks again begreen. I could do this easily, if I remove the transite pipe. I'm still curious about why I cannot use a double-walled liner inside a sealed cement/asbestos pipe that has several inches of space between it and combustibles (except where it ends in the basement as can be seen in the photo above).
As I understand it, using a large asbestos/concrete pipe... it just hasn't been done, and hasn't been tested, so isn't possible, despite it being possibly safe and effective, and in my case convenient.

 

[bholler]

As I understand it, using a large asbestos/concrete pipe... it just hasn't been done, and hasn't been tested, so isn't possible, despite it being possibly safe and effective, and in my case convenient.

Yes it may be safe we just dont know. Are you willing to bet your house on it? You say it has several inches of space around it yet in the pic you posted there is wood touching it. What is supporting it if there is space all around it?