Hi, I did a portable rocket stove/mass heater for my house. Because I rent and I'm not able to have a wood burner or rocket stove in the house. So what I did was I had 3 x 25 litre metal drums welded together with a basic 90° pipe inside it. Then packed it with perlite and slag rock that I found on a beach not far from a steel making plant. It had a metal lid on top of it. I then adapted/cut up a shopping trolley/cart, put a strong metal Base plate that can take the weight as it was pretty heavy. What I did then was I did a burn outside for 2-3 hrs till the mass in the drums was pretty hot(too hot to touch, then let it burn out and when the fire had gone out, pushed it in my back door and into my kitchen in the early evening and it stayed there till the next morning, and was still hot then. I regulated how much heat came from it by putting foil over the top of the flue pipe, as hot air rises from the inside of the upright as it was heated/warmed by the mass. I did use thin pipe which burnt through after two years but it kept my 3 bed house toasty warm through the night even on cold nights here in the UK. It was even hot enough to keep the house warm through to the aftenon the next day so was near enough piping hot for 20hrs. I've got thick steel pipe this year and will be changing it to a 2 drum rocket stove as the 1st one was VERY HEAVY. Hope this is helpful.