new guy questions

hello all i really appreciate all the free advice and help learnining all i have recently about rmh i have devoted considerable time to watching videos and researching old and new tech relatrd to this subject since i accidently discovered mass heaters and rocket stoves about a month ago i have spent almost every free min i get to researching them i have for a long time heated my house with a super conventional "earth stove" witch i love but i see the awesomeness that could be with rmh tech my plan is to have my own when winter hits next year my big 2 qustions among others are 1. exact relationship of barrel and riser height . 2. what do you think of using a discarded fuel oil tank of about the standard 250 gallon home style as the base for a sort of portable rmh , build the j tube inside on a bed of sand cob around fill with gravel cut top front quarter off tank use rear top quarter as "barrel" some heat exchanger tubes run thrue foced air from my non used funace also cold air intake from said funace sucking heat from rmh and distributing it . anyway long time listener first time caller thanks for disregarding spelling and grammar flaws.

2. what do you think of using a discarded fuel oil tank of about the standard 250 gallon home style as the base for a sort of portable rmh

I just want to say research how to cut or weld an old fuel tank before hand. Many people have been blown up working on EMPTY tanks. Even empty for years can still be dangerous. Fuel starts to come out of the metal when heated and it only takes a little bit of vapor in an enclosed or partially enclosed vessel to go boom. I have cut open propane tanks the have been empty for years and am amazed at how much  and long a flame will burn from an old tanks. I had one filled with water while I was cutting it and the hydrocarbons released burned on top of the water. It was still sketchy even filled with water.

YES you are very right my first and only bad mistake was an "empty" clear coat barrel we wanted to use at my friends house as a insert for his fire place we washed it out several times we thought that was good it was not talk about rocket. i also want to ad after looking at posts on here i now know  paul will ask if i had the book and as iwould love to support that type of thing i do not have the means to do so but if i save so much on heat in the winter maby i will be able to. for now my system will be cheap or free but i do very much wish i could contribute and help