Many flues / chimneys become one ?

If I build a large underground wofati, with up to 10 rooms under the larger roof, each room having it's own mass heater.  Is it OK to tie the chimneys together at some point so that there is only one exit hole out of the large common roof?
If so, how would that work?
Small pipes become one large pipe?
If two fires are burning will they back feed into the others?
Would you need some sort of "valving" or shutoffs to isolate each one?
Other concerns?

Hi Miles ;
Wow , that's a tough question.
I have not heard of anyone trying to do this before. Maybe you can be the innovator on this!

First let me ask you a few questions.

What size RMH's were you thinking?  6" ? 8" ?
What style of RMH were you pondering?   Standard J tube?   Or were you thinking Peter Berg's Batch box style?
You mentioned 10 burners. Would they all be running at the same time?  

I am not at all familiar with wofati's.  I will assume they hold heat well.
Are they tall and open ? Or standard 8' ceilings ?
How involved is it , putting a chimney thru the roof ?  
Could you use one super size batchbox in a main room and one smaller B.B. at each far end ?

Here is an off the cuff idea.  You may not like it...  
If you end up with 10 six inch burners.If only some were running at the same time you MIGHT be able to plumb them all into a 3'  chimney (culvert could work). The majority of the 3' chimney would need to be indoors and warm. Any sticking thru the roof would need rock wool or some type of insulation to keep it warm.

That's a complete guess on my part. Might be all ten could run into a 2' or might need a 5 foot dia. chimney...
Using block off's to control which rmh is open to a smaller standard size (class A) chimney might work, but only if your confident that a "helper" will not think it chilly and start an extra stove.

Hopefully others will chime in with more ideas!

Miles Flansburg wrote:If I build a large underground wofati, with up to 10 rooms under the larger roof, each room having it's own mass heater.  Is it OK to tie the chimneys together at some point so that there is only one exit hole out of the large common roof?

Miles, it won't work unless there's only one heater running at any given time. All the others should be closed very tight. If not, the heater that's running will be hampered by other heaters feeding air (or worse, exhaust gases) into the main outlet. Two fires burning at the same time will influence each other. There's also a large risk of one that runs well and the other feed small amounts of smoke (and carbon monoxide!) into the living space. It's not allowed in building code, and there's some reason to it.

Imagine one great house in rural England, all rooms having a fireplace and separate chimneys.
Those 18th and 19th century people weren't stupid, they knew combined chimneys are dangerous, asking for trouble. Please don't go that route.

It's not separate chimneys per say but separate flues. So yes to the OP you can put them together, but not into one flue

The chimney on the left here has 4 fireplaces and the one on the right has 2, you can clearly see the respective number of pots on each chimney but there are not 6 separate chimneys on this house. (It was my grans)

I've lived in a house with multiple fireplaces that went to one chimney flue.  Each fireplace had a damper as per normal and a different damper for not in use.  It was important to shut down the others before lighting one of them.  When wanting to light more than one, they needed to be lit in order or have a good draw before starting up the next one.  It wasn't easy for people to figure out and caused problems.

I like the houses we've had where the different fireplaces share the same chimney but they each have their own pipe all the way to the top.  Much easier to deal with and far cheaper to clean.

OK, thanks for the info all, we were talking in another thread about a possible building at the lab in Montana and I was wondering how the heat system would work.

You could potentially make a larger hole for the roof penetration and run several ducts inside it. I don't know about making one for 10 ducts potentially 6"+, and unless it was perfectly central then I'd imagine it might be a bit long of a run for the furthest heater. If the design is going to use an Oculus, then I don't know how that will affect things. It might not look great to have all of the ducts go up the center, and I don't know how wind could come in to play with having exhaust ducts next to a large opening in the roof. It might be better to run a few ducts side-by-side to a few larger roof penetrations towards the perimeter.

The idea of minimizing the number of holes in the roof is a good one. Instead of punching 10 separate holes evenly spaced around the roof, having fewer holes would reduce the chance of leaks and minimize troubleshooting any leaks that do crop up. If the building were freestanding it might be good to have them exhaust individually through the wall, but I guess that wouldn't be any better for earth berm walls.