Contact Marks Supply in Shenandoah Pa. He sells these new for about $595 ready to go. I have one that I got for less than that piped to my my oil boiler and it heats our hot water via a plate heat exchanger. I put in isolation valves so I can heat the house or the DHW or both at the same time.
I use about a hod of coal a day, hence the name Bucket a Day (BAD). The guy that sells these at Marks Supply modified his by putting a larger barrel on his and heats his house all winter with the little guy. Kinda like a chubby with a cast water dome on top of it. We nicknamed ours R-2 since he kinda looks like a small version of R2D2.
I heat all our DHW and the house in the shoulder months with it. That's when it's too warm to run the stove but you want a little heat. If I am heating the house via the BAD I burn it a bit hotter and I might use 2 hods a day.