Gene Beine

That's a good idea Glenn. I use the garage almost every day and I've been heating it with a fuel oil salamander with the door partially open. Not really good for one's health. Maybe the rocket will at least help maintain the heat once the salamander has it up to temp.
I'll start looking for materials for a bigger system.

I live in central Wisconsin. This will be to take the frost off some of the tools while building furniture in an insulated and drywalled 26x32 garage. This will at least be a good learning experience and all the materials were free.

So far I have 3 3/4" id square tube for the j tube, welded to a 3/8" steel plate. I test fired it last night with a little wood and a waste oil drip. The temp was 15 degrees at the time. Fired great. A 15" diameter water tank will go over it. I haven't figured the exhaust size yet. My main concern right now is riser thickness.

Howdy, I'm new here, even though I've been studying the content of this forum for a few weeks now. The knowledge here is fantastic.
I'm in the process of building a rocket shop heater. I made the heat tunnel and riser from .25" square steel tube. Now I see that this will just be a form for the castable fireclay and perlite. Before I make the outer form, how thick should I make the burn tunnel and riser?