Building a chimney for our camp

[PatrickBesong]

Being the DIY'r that I've come to be known as, I've been asked to build a chimney on my family's camp. It's a prefab log cabin type of building. They had someone build them a stone wall where a stove pipe goes out through a crock and they had a steel pip going up through it. They had a good foundation for the chimney poured before the building was set in place. I'll be using chimney block and liners to construct it. I understand that I need to keep the chimney at least 1" from the framing of the house. I have a few questions:
• Will the metal ties that hold the chimney to the house work well if it's an inch away?
• Should there be some kind of barrier in addition to the 1" clearance? Sheet metal?
• The crock that goes thru the wall only protrudes about an inch past the wall. How will I tie that in with the liner?
• Some say the holes in the chimney block web should be filled with mortar. Is that true?

 

[tiber]

I'm wading through all this crap at the moment with the forums, code, township, etc. I'm adding a chimney to my house since the "fireplace room"has a fireplace which is laughably small. R numbers for materials aren't hard and fast, they're a general analysis of lab results. For air it's even more of a crapshoot. The math looks sound until you find out that home depot board you bought is too thick or thin or otherwise has some weird defect. Low quality controls on materials mean you should over insulate or pay a bit more to get the good stuff.

Here's the list of R values:
http://www.allwallsystem.com/design/RValueTable.html
Guess LOW for all R values.

If the chimney is made with clay tiles, you're pretty much golden because this is how they all work. You put in the clay flue tile, you use a liner, you can put anything you want in there.

Air gaps are R1.

If the chimney has 8" (eight) inches of rock between the cabin and the wood, that's R 2. It gives you a total R value of around 3. (If it's all brick, it's closer to R1.8).

Hearth pads, the kind you buy, are R1 and the "high end" ones for nonUL stoves are R 2.5 for reference.

On the other hand if you fake it with class A in there, no-ones going to know and it doesn't care at all about the chase.

 

[webby3650]

I would forget the Clay tiles and go with insulated SS right from the start.

 

[DAKSY]

+1 for the SS. Class A is the way to go.
You'll STILL have clearance requirements to combustibles,
but, all in all, a safer set-up.

 

[PatrickBesong]

I already have all the materials onsite. No going back now.

 

[webby3650]

It only takes 1 flue fire to wreck all that hard work, then you have to install SS anyway. I inspect 100's of flues a year, I see a bad clay flue nearly everyday and I am yet to see a SS flue with a problem even after a flue fire. Although, I do see lots of well constructed and maintained clay flues, do lots of research and good luck to you!

 

[PatrickBesong]

Well I got to the point of cutting the siding off where the chimney will go. Under the siding is the OSB sheathing and under that is the rock from the hearth on the inside of the cabin. I thought of leaving the OSB board on so I'd have something to nail the straps to (that keep the chimney attached to the camp), but If I cut that off, couldn't I just cement the chimney blovk to the back side of a hearth instead of using the straps? Or should I try and drill through the back side of the hearth an screw the straps into the rock?

 

[begreen]

I'm no expert at this at all, but am astounded that one would undertake such a project without prior knowledge and planning. The risks of doing this incorrectly are considerable. If it were me I would meet with a mason that I respected and pay him as an adviser if need be. There are several important steps in this process including the foundation pad be appropriate for the soil type and height of the chimney. Then there are clearance issues and proper sealing and caulking to be considered. As for the thimble, the rules are pretty clear. It needs to have the proper clearances from combustibles in all directions.

This article should be helpful: https://www.hearth.com/econtent/index.php/articles/installing_a_woodstove

Masonry Chimneys

The details as to the building of masonry chimneys are beyond the scope of this document, however there are a few safety and performance issue to keep in mind. It is commonly known in the Hearth Industry that 80-90% (or more!) of the masonry chimneys in the US are constructed improperly. The sad truth is that some masons spent so many years building low-temperature chimneys for oil burners, gas burners and fireplaces that the art of proper chimney construction has become almost lost.
What’s wrong with most masonry chimneys ?

* They are often oversize and not insulated, resulting in poor draft and excess creosote formation
* Proper clearances to combustible (wood framing, siding, etc.) are not maintained
* No room for expansion of the flue tiles, resulting in cracked and damaged liners

These deficiencies can be addressed during new construction by a competent mason, and a properly designed and built masonry chimney is a work of art that can last for generations. An existing (but deficient) masonry chimney can often be brought up to spec by installing a UL approved stainless steel liner system. This provides an extra margin of safety as well as improves draft and simplifies cleaning.

For the proper information on building masonry fireplaces and chimneys, see the links below:
http://www.gobrick.com/BIA/technotes/t19b.htm
http://www.maconline.org/tech/construction/chimney/chimney.html
http://www.bia.org/html/fireplace_and_chimney.html

Things to Remember about Masonry Chimneys

* The flue liner of the chimney should be the same size (or just a tad bigger) than the stovepipe size,
* The chimney should be located inside the building if possible, and insulated (with vermiculite or other masonry insulation
* The flue liner should be either a “cast-in-place” type (ask your hearth dealer) or other form of constructions which allows for expansion.
* Most existing masonry chimneys need to be relined with stainless steel pipe

 

[wellbuilt home]

You don't have to much to worry about .
Just remove the wood siding with out ripping the building paper .
leave your self a extra 1/2 " on both sides and lay the blocks 1.5" from the OSB place the wall ties 1" from each corner and fill with morter 3" wide , dont fill the whole space between the block and wall.
stack the clay flue even going up inside the block , don't drop the mortar inside the chimney wile working .
use a good type s mortar not home depot stuff .
tool the block joints as you go up and use fresh mud so the chimney is strong .
chimney must be 2' above the peak.
Don't cement the chimney top to the flue I like to use foil wrap around the clay so the flue can expand and contract when it heats up and cools
Uninsulated chimneys build alot of creosote so clean it often.
leave a clean out at the bottom .
Chimneys where made out of block for many years just reline it when it needs it . good luck .

 

[PatrickBesong]

Thanks for your replies. I am thinking of just removing the OSB board as well, since the hearth was built up to it from the inside, so just behind the OSB is the stone for the hearth. I figure I can just cement the chimney blocks to the back of the hearth wall as I work my way up, since there will be no combustibles behind the chimney until I get to the framing at the top of the wall, which I can notch out for an inch or so clearance, leaving an air gap there and on up to the roof. I think my biggest problem will be that the crock going thru the wall is slightly wider than the flu's liner blocks, that is, I probably need to reduce the diameter of the crock coming thru the wall to go into my flu liner somehow. Will a smaller crock fit within the wider one that I can just cement in place (using the special liner cement they purchased) or do I really need to put a smaller crock thru the wall? I also though of just using stainless steel thru the crock into the liner. Any thoughts?

 

[webby3650]

Thanks for your replies. I am thinking of just removing the OSB board as well, since the hearth was built up to it from the inside, so just behind the OSB is the stone for the hearth. I figure I can just cement the chimney blocks to the back of the hearth wall as I work my way up, since there will be no combustibles behind the chimney until I get to the framing at the top of the wall, which I can notch out for an inch or so clearance, leaving an air gap there and on up to the roof. I think my biggest problem will be that the crock going thru the wall is slightly wider than the flu's liner blocks, that is, I probably need to reduce the diameter of the crock coming thru the wall to go into my flu liner somehow. Will a smaller crock fit within the wider one that I can just cement in place (using the special liner cement they purchased) or do I really need to put a smaller crock thru the wall? I also though of just using stainless steel thru the crock into the liner. Any thoughts?

Re-sizing the thimble will depend on what size outlet the stove has, and what size the clay liners are, this all needs to be sized properly for code and for performance.

 

[PatrickBesong]

I believe it's an 8" stove pipe, so the thimble is probably 8 3/4" or so outside diameter. The thimble is I'm guessing a 1" wider than the liners they bought for the job, so that's a problem.

 

[webby3650]

Is the thimble clay? If so, 8 3/4" OD makes it a 7" thimble ID, which is too small for an 8" stove. What size are the liners?

 

[PatrickBesong]

Well I'm pretty sure it's an 8" pipe going into the thimble. The thimble is slightly wider than the liners. Not sure exact measurements. I'll have to go down and check again.