Heat riser

Hello my heat riser is 43 and now is 47" tall from the bottom of the burn channel to the top all fire brick. Do I need to insulate this ? I have the tank from a 40gal gas WH that I can use and that leaves me about 2.5" between it and the 55gal barrel one other problem I am having is IT WONT ROCKET I can start a fire and it rockets {everything is 7x7"sq then when I put the barrel on,it stops doing its thing and starts burning back with a 2,3,3.5 now 4" gap on top the feed tube which is 11.5" deep with the bottom all open around the bottom of the 55gal barrel or does this have to be closed and hocked up to a exhaust to work correctly?

David Marin : What is the actual size and weight of your fire brick ! If you have 2.5 inches all the way around, Not 1.25 on one side and 1.25 on the other you should
be good !

there is a rule that you should have already learned but right now is soon enough ! When the barrel goes on the vertical chimney goes up ! This is a test and auto-
magically tells you if your Rocket burners parts are correct. If after you put up the vertical chimney, say 10' up or 5 feet over the top of the next tallest object if it
works you are golden, finish your test build and move it inside ! If it does not work with the Tall vertical chimney then start at the beginning and eliminate all cracks
and make things smooth as you can. Try that and let us Know how you made out ! For The Good of The Draft ! big AL ! Welcome to permies