Large coal bed building up like that is indicative of not fully seasoned wood, that being said, the "old school" smoke dragons like the fisher would burn anything placed inside it due to air leaks and burn it down fast.
Wife and kids and I would huddle in front of the open fireplace alot and I would go through insane amounts of wood with little heat benefit. This past fall I installed a Pacific Energy Summit insert in my 2600 sq ft home. I've been burning 24/7 and the average temps in my house now are 75 on the first floor and anywhere from 70 to 72 on the second depending on what room your in. During those sustained cold "polar vortex" days we had I was able to keep the house in the mid to high 60's with ease. Now that the temps are in the 30's and 40's, on a full load the house will get 80 and we're crackin windows. LOL. I haven't used a drop of oil for heat this season, only hot water. This was the best investment I made in a long time. In all though I love my Summit and would recommend it. At the time I was also looking at the Lopi Freedom as well as the Avalon Olympic. They are all great stoves. I may actually put the Olympic in my second fireplace this next year just so I can utilize both fireplaces.
