I wanted to let everyone know that no matter what the hand fired unit, if you skip steps or do them out of sequence you may get away with it once or even twice, but it will eventually get you.
I have a Bucket A Day water heater that I plumbed to heat all our domestic hot water via thermosyphon. I had cold water coming from the bottom of a 40 gallon tank into the lower fitting on the BAD and then piped the hot water from the BAD into the top 1/3 of the tank. It worked great!! That worked really good but the water tended to get too hot so I need someplace to put that heat. I pulled up a bucket and sat and looked at the arrangement and had an epiphany.
Heat the domestic hot water and the house with the same unit! That fact that they were at different pressures could be handled by utilizing a plate type heat exchanger for the domestic water that I had left over from a previous solar heating system I built.
I plumbed the B.A.D. so the discharge of hot water from the top went into the top left corner of the boiler and via a T also goes to a plate heat exchanger that heats all our domestic hot water in a 40 gallon hot water tank. The return from the heat exchanger went into a T at the lower right corner where the boiler drain had been. It worked GREAT. The house is holding at 72 and the hot water is still hot enough where a mixing valve is called for. That will be a future project. I started experimenting with coal sizes to see if I could extend my burn time.
I had been burning pea size and got excellent heat but short burns of only 4-5 hours. I put that off to the small cylindrical space above the grate not holding enough coal. It holds about a total of 10-15 pounds of pea coal full to the top. I tried topping it off with rice to slow down the burn but when I shook down it was too small and would pour through the grate. I switched to burning buck and it seemed to do really good. It didn't burn as fast or intense as Pea and seems to be a good size for the grates. I got up to 8 hour burns. I started filling it with buck and then putting about an inch of ash on the top to slow down the burn. That got me up to 10 hour burns. LOVELY!!
But I couldn't leave well enough alone.
I was given 5 five gallon buckets of damp fines. No idea where they came from but it's coal fines and previous experience showed the BAD burned anything with BTU value so I started topping off the buck with the fines instead of ash. It worked great. It was a little volatile when I first added it but it cooked down OK. After using a full bucket and went to the second bucket and that's when it happened.
I was late leaving the house for an appointment but I knew I would be back in about 4 hours. I did a reload with buck to the 3/4 level and topped it off with an inch of fines. While I was holding the loading door I noticed that in my haste I had forgotten to open the MPD and the ash door.
I thought I would close the loading door, open the MPD then the ash door.
As soon as I closed the loading door and took a step back, It rumbled and fire belched from the loading door toward my belly, out the ash door toward my ankles, and fire came out in a complete circle where the circular heat exchanger bolted down onto the cylinder. I stood there in shock as it all happened so fast.
I started checking the flue pipe joints and they held. The barometric damper was flapping like crazy. I poked open the Baro flap and looked in and saw something that resembled the northern lights. I slowly opened the MPD to full open and it stopped. I opened the ash door draft regulator and checked the rest of the system.
Always always always follow sequence. You may get by with it once or maybe even twice but eventually you will pay the piper.