Question for stone masons

[meathead]

I am having a timber-frame home designed and need to determine chimney dimensions for roof framing. I am planning a field stone chimney with two 8x12 flues. Can anyone help me out with approximate dimensions of the chimney? Assuming unlimited supply of stone in any size, what is an ideal wall thickness for a field stone chimney?

 

[Yagminas Masonry and Wood-heat]

I'll try and help a bit....
I have found the best method is to build the chimney out of 4" block with block wire protruding 6" out as much as possible. Then lay the stone 4"-6" deep up against the block using a VERY dry almost crumbly but rich type "s" masonry cement mix. Make sure your footings can handle all the weight....like 30 tonnes on a 35' monster. Tie the block wire into the stone cladding as much as possible. Anyways rough size would be 32" x 48" finished... My Ideal wall thickness would be about 10" using stone and 4"block. Don't forget 4" solid between the two flues....

Kev

 

[begreen]

If this is an exterior chimney consider having an inner and outer wall with a gap for poured insulation.

 

[meathead]

Thank you very much for the help. It is an interior chimney for a masonry heater with a second flue going down to the basement. By the time I build it I will have read enough textbooks and attended enough workshops to pretend I know what I'm doing...but I need to let my frame designer know what size hole to put in my roof frame now...little intimidating. I am going to figure on a 10" wall thickness around the flues with 4" solid between them. Thanks again!

 

[begreen]

What will be basement flue be servicing?

 

[webby3650]

Some masonry heaters are designed to use a class A chimney.
Would this be a possibility? It would be a better choice for that basement flue too.

 

[meathead]

Basement flue will likely service a wood stove, with a 6" liner if needed. I'd like it to have the capacity to run whatever future inhabitants want down there. I ended up planning for an 8" flue to the basement, with 3'8" x 2'4" chimney dimensions (~29' height off the first floor deck, ~9' more to the basement floor). The maker of the heater core said you can switch to class A after 8' of 8"x12" masonry chimney, but the chimney is a focal point in an open floor plan with cathedral ceilings, and I'd like to do stone to the top. Making the switch somewhere before exiting the building envelope will get some consideration. Fire away with any thoughts. Thanks guys.

 

[Prof]

I'm actually planning a similar build for next year--masonry heater on the first floor and stove in the basement. I'm using class A chimneys that will be faced with field stone. When I was working on this aspect with the architect, he determined that a 2 flue chimney will fit between the rafters without much concern (there is about 3.5 ft to play with here). He placed the chimney between the 2 rafters and this guided the placement of the masonry heater as well, which ended up about a foot from where I had initially anticipated it to be. No one except me and the contractor will know that the chimney is 2 class A chimneys in a chase vs. solid masonry. It all works out on paper so far--I have a competent contractor who can hopefully translate this into 3-D!

 

[Ashful]

I am having a timber-frame home designed and need to determine chimney dimensions for roof framing. I am planning a field stone chimney with two 8x12 flues. Can anyone help me out with approximate dimensions of the chimney? Assuming unlimited supply of stone in any size, what is an ideal wall thickness for a field stone chimney?

I've owned many field stone chimneys (two in my current house, alone), and the dimensions are pretty standard for 18th century houses built around here:

1. Adjacent to exterior wall: Exterior walls are typically 18" thick, and chimney walls are also all 18" thick, such that it protrudes flue width + 18" from interior face of exterior wall.

2. Built within exterior wall: Wall is built as 24" thick, and narrow flue is built by turning stones on their edge (exposed broad side) within the wall. These are almost never still functional after 200+ years, and are often the reason for stone wall failure.

I have one of each type in my current house. As is typical, my chimney built according to method 1 is fully functional (although lined for a stove), and my chimney built according to method 2 was decommissioned many years ago.

 

[Prof]

So Meathead--who is doing your heater design. I'm working with Alex Chernov?

 

[meathead]

Prof - I'm planning to use the heat-kit core with a heated bench on the front and a left side chimney exit. I just checked out Alex Chernov's gallery; his stoves look great! Are you having a timber frame built (guessing yes if 3.5' rafter spacing)? My build is going to be a slow and steady DIY process a few hundred yards from our current house. This year's step is just getting the foundation / frame / shell designed and a bandsaw mill set up. Yours will probably come together about a decade quicker than mine - I'd love to see progress on it if you start a thread with pics somewhere.

 

[Ashful]

+1... please post a link in this thread, if you have a thread on your build, Prof.

 

[Prof]

Prof - I'm planning to use the heat-kit core with a heated bench on the front and a left side chimney exit. I just checked out Alex Chernov's gallery; his stoves look great! Are you having a timber frame built (guessing yes if 3.5' rafter spacing)? My build is going to be a slow and steady DIY process a few hundred yards from our current house. This year's step is just getting the foundation / frame / shell designed and a bandsaw mill set up. Yours will probably come together about a decade quicker than mine - I'd love to see progress on it if you start a thread with pics somewhere.

Yeah, it will be timber frame. I'm still mostly in the planning phase (with the exception of clearing the trees)--I anticipate a start in April of 2015. Once things are underway, I'll post some pics.