The right chimney Choice

Gary B. here from MN. I am about to start a stove build and I am looking for some advice. Try2hard and I have been talking about my build on the side. Between us we have decided to go with a rocket stove heater some what like PPotty's. I will be using a 6 inch stainless riser insulated (.280 wall) 42 inches high. I have 60 -70 cords of white oak that is cut to 20-22 inches long, so my burn box will be longer than PPotyy's. Instead of using a LP tank heat exchanger I will be building a custom heat exchanger out of thin stainless and some vertical 2 inch stainless tubes. Ok now that you have an idea of what I am doing here is my question. Right now my chimney in my shop is a traditional cement block and tile with the flue being 8 inches by 12 inches. This has worked ok with my old stove but now I am wondering with my new stove what should I do?? Should I use it as it is? Line it with a stainless liner? If so then what size should I use.  I can tell you my chimney is 22 ft high from floor(4 feet above peak). I am asking anybody for advice. Thank you in advance.

use rule of thumb what goes up must come out

so if using 6 the omtimal is 6" flue however using a vortex you maybe able to drop down to a 4"-5" flue as the vortex slows down the rate of upward air up the tube

as with the older type straight up then it would be what goes in must go out but creating the vortex in the tube slows the rate of upward draft

as goes for testing you could use the old chimney for testing purposes if decide to change it then insert the correct flue liner in the chimney but should be adequate

If the height or composition of your chimney is your concern, then consider that the final output of a rocket stove is much cooler and much less laden with combustibles than the output of a standard wood stove. This means that the composition of your chimney is probably fine as is, however you might consider that such a tall stack may make it hard to get a draft started. Once it gets going, it should work well, though.

Cheers.

JD