Okay, time to start at the beginning. Apparently I need help on coal furnace designs and installs
First, some background.
I have a circa 1950's round firebrick lined combustion chamber with a circular grate around the perimeter and clamshell dumps in the center. The outer grate is now broken, but shakes mostly okay with the occasional poke at it and remove clunkers. The grate does stay in place but doesn't really rotate, but it does "bounce" which does okay.
It has a firebox approx 20” diameter, lined approx 20” high with firebrick, about 6” more to the exit flue and about 8” above that to a domed top.
The flue is 8” round to a VERY heavy kidney I built using the pattern from the old, burnt out one. I believe it is 14 gauge, with 10 or 12 gauge top and bottom pieces. Plasma cut and welded together. I didn’t want it to burn out
The exit flue from the kidney is about 4” or so lower IIRC than the entrance flue and has a plate at the entrance flue (I think to divert the flow so it circulates in the kidney instead of just flowing straight through).
I have a very heavy walled steel exit pipe from this exit flue of the kidney welded in place to allow the shroud to cover everything. The pipe is about 8” long, then 90 deg up, about 4’ vertical black walled stove pipe with a cast iron manual damper, another 90 deg to horizontal, about 12” to clay thimble. Thimble is about 10” horizontal into chimney.
Chimney flue has a 17” x 17” chimney block so that would be 8” x 8” flue. I can’t get to roof right now, it is on 3rd story and I have to borrow a ladder for that. I estimated visually where the exposed one meets the brick at the top and measured, then called the place where I got the 3 block I added 2 yrs ago and got their sizes. Pretty sure it is correct.
My furnace is in basement, 7’ ceiling, below grade in the back. Chimney starts on grade and goes in a brick encased double chimney on outside of house (each chimney with its own blocks and liners, but sharing the brick outside) and extends 3 3/4 blocks above the peak of the roof. Chimney is basically centered on peak.
We have a VERY LARGE oak tree about 100 ft upwind from us. We are in a hollow and the tree is more than twice the height of our house.
I build a custom shroud out of 14 gauge steel to top of furnace, then added standard galvanized box for about 18” above that for ductwork. I used homemade Z seams to attach them. It is *mostly* airtight. I’d say leakage is in the single digit percentages.
It has a box on the side with its own enclosure for filters and blower motor sticking through a hole in the side of the shroud. A little air leaks out of the bottom where it meets the floor, but not much. It is a big old slow and steady blower the runs mostly full time once up to temp.
The furnace is steel. I rescued and refurbished it a few years back, even painting it with high temp black paint after sandblasting.
The loading door is rectangular and steel with a steel baffle on the inside covering the door slide vents.
The ash door is large rectangular with a flap style damper. I believe it is setup for an auto-damper motor, which I have, but I’ve never used or setup yet. I haven’t been happy with its performance yet, so not ready to automate. Maybe that is backaswards???
Now the problems.
Although it puts out a LOT of heat, it seems like I always have to have a nearly full firebox to get good heat and keep shaking and stoking it to get a hot, effective burn. A small fire just doesn’t make much heat or last very long.
When I can get it banked nicely, it likes to get crusty and hollow out by burning all the coal under/inside the crust. Trouble is, when we poke it down there may not be enough hot coals to load it back up without a few intermediate loads and checks to build up the bed of hot coals.
This all makes for a fire that needs nearly constant attention. It heats, but overnight is a bear. I have to start a few hours before bed and fire it hot to get hot coals and bed it over. Late night and early morning, else the fire will burn out. It is usually quite cool in the am and we have to stoke it with wood to get it fired up again. Not rebuild, but definitely build it up.
If I cut it down too far, it drops temp and starts to smoke instead of putting out heat. No smoke in house, except when fixing the fire and forgetting to open the stove pipe damper first
We get a LOT of ashes. About 3 5-gallon buckets in 2 days.
These are worst case. Not always that bad, especially if I have it HOT, but then it uses a lot of coal. But these scenarios do happen about half the time- enough to classify it as a problem.
I have a few possibilities and am looking for some input?
1. Chimney changes. Extend chimney, reduce it with a liner, add barometric damper
2. Seal up ash pan door and shaker rod holes and add a fan to ash door using pipe to direct air and protect fan.
3. Seal up loading door
4. Reduce flue sizes on furnace and/or kidney.
5. Some sort of auto controls?
6. Line more of firebox with firebrick. Current firebrick are in poor to fair condition and it is HARD to find curved, so likely going to be doing some 15 sided polygon or something soon anyways
7. Add internal deflector plate or baffle of some kind inside firebox- welded or suspended?
8. Add baffles or air channels or magic pixie dust to firebox?
9. Change coal to other size, heat range, or hard coal?
I have access to a manometer (borrow) but don’t know what its value should be.
I am using nut sized soft coal from local source in Western PA. Tried some “hotter” coal, but it was harder to light and that seems to be something we do (build it back up) quite often.
Oh, our house is just under 4000 sq ft and half of it is semi-remodeled and well insulated while the other half is not and poorly insulated.
When fixing the fire and the chimney is smoking, the smoke goes out the chimney and often rolls down the roof and side of chimney, leaving very light soot. I have about 2-3 inches of soot in cleanout from last season.
I can build and fabricate most things. Have access to plasma cutter, torches, MIG, grinders, etc. Just don’t know *what* to change???
I am obviously missing something! Please help me understand *what* it is I need to modify and tame this beast. We love the hot air and the way it heats, but not being a slave to it. Funds are limited, but “heat” is not an option
Sorry so long, trying to be complete.