It really comes down to how well sealed and insulated your space is. I can give you two real-life examples to consider:
First I have a new, very well insulated (14" of Roxul bats in the walls, 24" in the ceiling) workshop that is heated in winter quite well by a small daily fire in about a 30,000BTU stove. This is quite a small wood stove, but it heats the 20'x35'space quite well for the day using only 3 or logs. The modern insulation and sealing makes all the difference.
In contrast, my very old and non-insulated double brick house is heated by a Jotul 'Big Bear' - a much larger woodstove - and it can really only keep things nice down to about -5 outside. Colder than that and i have to turn on the furnace. At 0 degrees outside i will burn 16-20 pieces of wood in my house, vs. the 3-4 in my workshop.
I had a jotul602 in an 8 x 12 cabin in West Virginia, Winter highs often around 15 - 20 f . The only way to avoid overheating was to leave a window open and run a smoldering fire, meaning lot of creosote in chimney, necessary to clean chimney regularly, and not so good for environment. Now we have 2 sardines in 10 x 12 cabins here in northern california where the climate is pretty mild, lows around 40 in winter. Not really comparable to your situation.
