I just finished my stove made from a hot water heater. Some details are a catalytic cumbustor with a bypass lever, preheated primary and secondary air, window air wash and a large chamber above the insulated firebox for a water coil (not installed yet).
It burns very clean and it will run at least 12 hours with a good bed of coals in the morning.
My goal was to make a stove that rivals a blazeking and use recycled materials. I bought a catalytic cumbustor for $130 and also needed some new steel that I could not scrounge. Around $200 total.
I'm not sure if the upright configuration is optimum or not so I may build another one with a horizontal firebox. I have an extra cat so my gf tiny house may get a new stove.
It's my second day running it. The metal is 3/16" so it's thicker than a barrel and those last several years. The firebox is lined with insulation I got from a boiler and a second layer of steel. Not sure of the surface temps. I'm getting a little to infatuated with building stoves so suppose I should get a temp gauge.
My goal was a stove I could run on low and still burn clean. There is almost no visible smoke one it gets up to temp.
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