what kind of pipe is customary?

I've been doing research in hopes of adding a rocket mass heater to my homestead. I will be moving into a concrete block structure soon and it has concrete floors and a bricked area (partially up the wall and part of floor) in one corner for a wood burning stove. There is no chimney, but there is a hole for pipe....

Since I am in Mississippi, I don't need a lot of intense heating so a small bench would probably do. Also, the place is only 16x32 total size.....anyway, my question has to do with pipe that is used. I've been looking at options and there is a huge price difference between stainless steel and black matte chimney pipe. What type of pipe is recommended and does it matter? I guess I am asking why all of the videos I've watched are using silver pipe when there is a black matte option that is tons cheaper.......am I missing something that is only in the book? I am on a shoestring budget so every cent will count, but I certainly don't want to take any risks. Thanks in advance for any help on this.

The silver pipe you see is not SS. I believe it is just duct pipe, not chimney. It is cheaper than black matte, but cannot be used till the gasses are cooler. Not fire rated!

Kristy Cooper : Please goto> richsoil.com (our sister site) and click on rocket mass heaters, this will lead you to a series of 'Rocket' videos, the 7th, or 8th
one will show you how to prepare your barrel for use and also for providing a hot enough fire to change how the zinc coating is chemically bound to the
surface of the Galvanized stove pipe, after it has been heated outdoors the change from shiny to a flat gray shows the chemical recombining and the safety
of any use for this pipe, as the high temperatures of the hot exhaust gases are diminished within the first 6', any use of any pipe is allowed , cheaper is
always better, consider the pipe as only there to make the horizontal passageways out of cob, and you will be sure to pack the cob tight enough for good
heat energy transference !! Big AL

I thought I had watched all the videos but somehow missed that one. That helps so much. Thank you!