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[theronbt]

I am in the process of researching some ideas about building my own stove. My idea on the chimney is very difficult because I am wanting to make it somewhat like portage and main with the chimney going up and to the front then 180 back then up. I know this will be very difficult if possible but I think it will make the stove a lot more efficient.
My question is what is the best size chimney to use 6" or 8". And has anybody ever tried to use square box style tubing for the chimney instead of round ?
I know that every body has always used round but I was just wondering why. Is it better? Better air flow?
S it possible to use square tubing then use round when I come out of the stove?
Sorry if this is a dumb question. Just maybe there is a scientific reason why everybody uses round
Thanks

[mlappin]

Round tubing is more stable when expansion and contraction is figured. Also gives you the most surface area over a square tube.

You don't specify, but are you considering a standard build or a gasifier? A standard boiler could creosote up a flue like you're describing in very short order.

I'm sure somebody has a equation to figure stack size, but a simple way is to surf the net, look at commercial units and compare their firebox size to yours and see what size flue they use. Too large and you can loose a lot of heat out of it, too small and the stove may not breathe well.

[theronbt]

I am building a standard unit. I don't know the gasifiers well enough to build one.
I was thinking of using square tubing for easier welding and trying to keep as much chimney in the water jacket as possible

[BoilerHouse]

Give some thought as to how you will clean it.  A round brush is probably easier to get, in different sizes, than a square brush.

[theronbt]

I was going to go out the back of firebox go 90 up then bring it to the front and back to back and then up. I am planning on putting a small door in the front of stove so I could clean it out. Clean some from door some from above and the rest I would have to get from inside the firebox. I am not really sure if it will work the way I am thinking just trying to get more chimney in the water
Prob a brush of some sort not sure yet

[racnruss]

How about not doing the 180?  You could extend your chimney down in the rear of the firebox 1/2 way or so, then come up above firebox and 90 forward to the front of the stove in the water jacket, then 90 up through the roof.  You could have a cleanout door on the front of the stove and any creosote that you scrape off would push back and fall back down into firebox.  Round or square probably wouldn't matter that much I wouldn't think.   I believe Hoss boilers have square chimney sections in the stove.

If you search on Ebay you can find about any size brush square or round.  If the creosote gets hard, you may make a tool like a hoe with either a curved blade for a round chimney or square blade  if you went with square tubing.   

If you compare say a Heatmor 200 to a Nature's comfort 250:  similar boilers in size but Heatmor has 8 inch chimney and NC has 6 inch.