Logan Merrell

Hi bob, thanks for the reply.  
Yes it dose have a top, I just haven't welded it on yet. I wanted to figure out the issue of insulating the Riser before I welded it on the top. I haven't cut the hole in the bottom yet for the exhaust gases to come out because I wasn't sure what size I should go with at the bottom to go through my heated bench.

Hello all,
I have been researching rocket mass heaters a bit and decided to take a crack at one.  I built this cone completely from materials i had lying around.  
The feed tube and burn tunnel are built from 5 1/2" square tubing the riser is built from 5 1/4" round tube.  All of it is 3/8" thick.  
The feed tube is 8" long burn tunnel is 16" long and the riser is 32" high.   it all sits inside of an old propane tank.

My questions from here are.
1. Should I still insulate the heat riser?  I was hoping that being thick steel it would be sufficient.  I have heard people say the heat riser can reach around 2000*.  I don't really want to melt this thing.

2.  I plan on routing this through a heated bench in our basement.   What size exhaust pipe should I use to come out the side of the propane tank.   And what size should I use going through the bench?  I plan on making the bench 12' long with a simple down and back run in the bench and then tie into the existing exhaust pipe.

Here are a few pictures of what I have so far