I have mine set up in the basement piped to an old 30 gallon nat gas water heater that I pulled the burner out of so I am only using it as a storage tank. Tank was free and all the copper pipe was recycled from other projects. I also recycled 5 inch flue pipe from other projects. I did have to buy some increaser's to connect to the 7" flue pipe that the oil boiler had used. The entire thing installed cost me around $275.
I fire the little R2 (as I call it because it looks like a 1/2 size R2D2 from star wars) every other day with 1/2 charge of coal. Any more than that and if we aren't using hot water, the temp will go up to 210 F and the relief valve on the tank it's connected to will start to dribble.
Dimensions are about 14 inches wide by 21 inches tall. I had to set the baro to max pull, close the MPD, and keep the air inlet closed to limit the amount of draft pulling through the little puppy. It has enough air leaks on the ash door that it gets enough air to burn very nicely. So far I have about a 12 hour burn if it's fully charged with about 10 pounds of coal. A 1/2 charge of pea coal maybe six to 8 inches deep will burn for about 6-8 hours giving us pretty much unlimited hot water that ranges from 180-200 F.
Nope no tempering valve installed. It's just my wife and I at home and I figured out that's what the cold water faucet was for. We also have enough intelligence to realize the water is HOT and regulate the temps with the cold water faucet.
I installed it right next to the oil boiler, disconnected the flue pipe from the oil boiler, spun a 90 degree elbow and I am using the same flue pipe and chimney the oil boiler used. I'm heating the house with my little LL Econo1 and heating the water with my bucket a day. The oil boiler was taking about $50 a month in oil for DHW. I bought 4 buckets of pea coal for $12.90. I estimate that I'll get about a month out of the four buckets. My 5th grade math tells me it should pay for itself in about 8 months and then I start saving.
How nice to know I'm not sending a single penny to the middle east sheikdoms.