I'm planning on using my wood/coal boiler as a coal boiler for the first time this coming winter. It is a Hytec boiler made in Ma. in 1981 and the model name is Hydra Fire. I bought it new 27 yrs ago and only tried coal 1 time (had no clue what I was doing). I burned alot of wood in it over the years but gradually got away from using it and instead used a Tempwood wood burning stove in my living room-which isn't that pretty but burns unbelievably good! I described the wood boiler in another post looking for info but I got no response. The draft is controlled high and low aquastats made by honeywell that monitor the water temp. The unit is plumbed in parralell with my burnham oil burner. Their is a Grundfos circulator pump connected to an aquastat that pumps water through the boiler and these pipes connect to the main pipes that enter and exit the oil burner. Essentially, the coal boiler keeps the oil burner hot. For baseboard circulation the same circulator that moves the water from the oil burner also moves the water through the radiators even if the coal boiler is doing the work. There is one heating zone that opens to dump excess hot water if temps get too high-controlled by a valve and aquastat. The system always worked flawlessly after I tweaked the settings to work well with the oil burner. I did get away from using it though because I found my Tempwood in the living room to be so efficient. I burned less wood but of course I got no hot water.
Here are my main concerns. The burning rate is controlled by an aquastat that turns on or off a Honeywell Draft damper operator motor (a full on or full off motor with a chain attached to a flapper that controls whether air is allowed into the damper or not.) So basically it is either wide open or closed shut. I could adjust the limits of open and closed by playing with chain length and location. I just wonder if coal will stay lit if the damper door is closed for an extended time like when the weather is not too cold or if I were trying to just heat water in the summer??? With wood it was never a problem.
My other concern is the length of time that a load of coal will burn in this unit. The fire box dimensions are roughly 13-14" X 25" x 8". The 2 long sides of the firebox are angled so that at the bottom the width is 9" and at the top of the brick it is 16". The nameplate on it says it is designed for wood and anthracite. There is a long arm on the front to shake the grate. When you open the ash door there are 2 slots for running a long, flat bar just over the top of the grates for ?? It also came with a long rod with a bend on the end for cleaning between the grates I guess. The boiler has insulation under steel panels on the 2 sides and the back. I don't know how long this size firebox will be able to burn in cold weather. My house is well insulated-I built it myself 27 yrs ago. I already made the commitment to coal and just stacked 120 bags of Balshack nut coal the other day. Grates have about 1/2' spacing and I am guessing on what size coal to use since I lost all paperwork on this stove. There is NO INFO on this boiler on the internet at all!.
In summary, How long might this burn with that firebox size and do you thing the damper on/off control will work sufficiently well or might I have to always leave it open a little???
Sorry for the lengthy post but I'm new here and excited about going this route and I've been reading this forum non stop for days. I know I'll at the very least have to learn the art of coal burning and forget all my wood burning ideas-except for my ugly,trusty,tempwood-even the ashes disappear in that thing.