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Chimney Setup for RMH

 
pollinator
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Location: Northwest Missouri
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The gist of my question: How are yall setting up everything that comes AFTER the RMH?

All the specs for stove pipe, thimbles, and chimney supports come from the wood box heater world. Where flue gasses are ridiculous hot and you need all kinds of clearance and/or insulation. Plus parts are priced high to account for the heat.
I'm confident with my build regarding the first few feet out of the heater needing to be black stove pipe or pre-cooked galvanized (to account for the potential oxidation and accompanying health hazards) but how are you getting through the wall or ceiling without spending a ton on insulated thimbles and the insulated stove pipe they are built for?

In the RMH world, it seems that using single wall galvanized is fine, especially in the outdoor portion of the chimney. I'm just struggling to figure out how to piece things together since there are no cheap off the shelf parts to do this. And I'm not super sure yet if I'm going through wall or roof of my shop. Kinda depends on how these transitions would look with parts that are ok for the low flue temps of an RMH.
 
pollinator
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Matt,

after you run the gases through your bell--either using ducting or a stratification chamber--you can bring them  up to the ceiling using single wall stove pipe. The temperatures should be low enough at this point that single wall is recommended for cost effectiveness and its ability to shed a little more heat into the house. Once the stovepipe gets to the roof you have the question of whether you are building to code or not. Even with low temperatures I recommend buying a thimble for the ceiling, through the roof and using insulated chimney pipe for your chimney above the roofline. This not only makes the best transition through your ceiling, but eliminates fears of combustion.

The thimble and insulated pipe are going to be the most expensive parts of this stove, although you will see many examples across Permies of people only using single wall straight through the ceiling or wall, with DIY thimbles. Again, the temps can be low enough that this wont matter, but definitely are not up to code.

 
Rocket Scientist
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Hi Matt;

Both the rocket in my shop and our studio use proper thimbles but remain hvac pipe out the roof.
But however they only stick thru 18-24".  
 
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I used single wall hvac pipe out of the mass up to where I penetrated through the wall, then it's 800 or 900 dollars worth of double wall insulated pipe for a proper chimney out. This does a couple things, 1. your homeowners insurance has no reason to squawk or deny claims. 2. This will make for a easier to use, less finicky stove to start. If your mass is pulling tons of heat out, and your chimney outside is single wall and the temperature is cold outside, it may cool the gasses inside the pipe so much that they can't rise out the chimney!  By insulating that column of air penetrating to the outside of the house and ensuring that it is warm, will make your stove start up much better and easier for a novice operator to get going.
 
Matt Todd
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Eric Hammond wrote:I used single wall hvac pipe out of the mass up to where I penetrated through the wall



Where did you fall on the "galvanized fumes = bad" debate? Or did you pre-cook (oxidize) your galvanized HVAC pipe before installing?
Wondering if I should go with black stove pipe into my mass and up to the ceiling before transitioning to double wall above the roof as this thread encourages me to do.
 
Eric Hammond
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Matt Todd wrote:

Eric Hammond wrote:I used single wall hvac pipe out of the mass up to where I penetrated through the wall



Where did you fall on the "galvanized fumes = bad" debate? Or did you pre-cook (oxidize) your galvanized HVAC pipe before installing?
Wondering if I should go with black stove pipe into my mass and up to the ceiling before transitioning to double wall above the roof as this thread encourages me to do.



The flue pipe coming out of my bench I can rest my hand on most of the time.  If I burn a fire all day long it gets too hot to touch but I've never seen it over 160 degrees. Not nearly hot enough to off gas.
 
Matt Todd
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Daniel Ray wrote:Matt,
after you run the gases through your bell--either using ducting or a stratification chamber--you can bring them  up to the ceiling using single wall stove pipe.



Thanks Daniel. This train of thought ran me into another question: I'm using a 300 gallon steel tank for my bell. Thicker than a drum, already on the property, and internal surface area math comes out about right. I'm sticking in a 7 inch DSR2 core and I'd like to run my single wall black chimney pipe into the top, down to 8 inches from the bottom (somewhere off against a wall, not right next to the core.) So the question now is: is the inside of a metal bell too hot for black chimney pipe, usually rated at 800 degrees F?
 
gardener
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Matt Todd wrote:So the question now is: is the inside of a metal bell too hot for black chimney pipe, usually rated at 800 degrees F?


Temperatures have reduced significantly by the time they reach the bell. I have never heard of anyone having problems and think that your pipe should be just fine in there.
 
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