Wow, so there are too many pluses here to ignore... I'll still have wood in the fireplace insert (different chimney) and will probably also burn wood early and late in the season but I think I'm going to have to try coal.
Let's see if I can cover all questions...
The grates are in good shape and, aside from needing a little lube of which I'm not sure what to use, they work great. This furnace shows to have been tested in '94 but has only been in use for a couple of years. The guy we bought our house from got it from his brother 2 years ago. His brother had used it for a year and decided to go with gas.
The unlined chimney was what really concerned me but it sounds like coal is a better choice for my type of chimney. It runs through the core of the house, the only part exposed to the elements is what comes out of the roof and that is cement over brick so I have no doubt that it is in as good shape as the exposed portion in the basement. It's pretty good sized, not sure if the interior dimensions but will try to measure this weekend as I want to clean the stove pipe again just to check to see how much creosote has built up in the 3 weeks since I had it apart. If I recall the chimney is 2 or 3 layers thick (of brick) and looks to be 4.5 bricks wide on each face with a half inch or so of mortar binding the bricks together. All of the brick joints are solid, no crumbling of the mortar so no need to point... happy about that.
I do have the manual to the furnace, soft copy anyway, the company is still in business (link below) and I downloaded the PDF. I'm including the link as I haven't gotten the pictures from my phone to my laptop to post them yet. And to the mods if posting the link breaks a rule please accept my apologies.http://www.brunks.com/bruncofurnaces.html
Standard front loader, ash door below with a stoker blower between the loading door and the ash door. I read on another forum the somebody with the same furnace adding a spinner vent on the ash door to add additional air under the coal bed. The loading door has one of these vents two but I think the issue was that the stoker blower didn't force enough air to completely burn the coal. Works fine with wood though.
I really would like to get away from burning so much wood, I burn slow over night and during the day and am amazed at the creosote just on the door of the firebox in 3 weeks. I've got about 3 cords in the basement now so I should be good for a few months but if I can mix and match, obviously not burning both at the same time, I would like to pick up some anth and give it a try. Poking around the site I understand that firing is a bit different so that'll be fun to master. I do like the comment about lower stack temps especially with some creosote that will build up if I burn both during the season.
The stack out the back is 8 inch necked down to 6 inch for the pipe into my chimney.