I've been wanting a source of wood heat for years but for insurance purposes and the lack of a good place to place a wood stove in the house i decided an outdoor stove would be best. Outdoor boilers are by far the most common but I could not figure out a way to build one that I could do on the cheap, like extremely cheap. So I came up with an outdoor wood furnace.
The furnace i came up with is an old electric hot water tank for the fire box which I placed inside of an old oval steel water tank (same shape as fuel oil tanks). I welded them together, welded the chimney and door on, made a deflector that I believe is creating a secondary burn.
The chimney is 6 feet of 6 inch steel pipe welded to both of the tanks with triple wall sections slipped over it that were removed from the house since we switched to a high efficiency furnace that does not require a chimney through the roof.
For the fan I took a radiator fan out of an old 90s car (it had 2 so I have 1 spare) this way I can run it on a 12v system so I can still have heat during a power outage. I ducted both the cold air return and hot air delivery through 10 feet of coroplast that I scrounged up.
I routed it through an old air conditioner unit that was basically build into a window that I could not remove without destroying the window, so I gutted out the unit and ran the coroplast ducts through it.
The only cost that went into this so far is welding rods and the door gasket, everything else was scrounged from one source or another, heck even the tape on the coroplast was a dumpster find.