To my recollection it was in a bakery the fire begun and spred rapidly over the city to the chimes of churchbells. When the fire was extinguished only 9 of all of the city's lots were undamaged by the fire. One of them being the Bishop's residence. The church had damages to its roof and outer walls.
When you go sight-seeing I think you should pay attention to this discrete corner of the city center. It's the corner between Drottningatan and Östra Torggatan that housed the Bakery some 150 years ago. Today there's a sign on the wall saying it was here that the fire started and what parts of town survived. The sign is only in Swedish unfortunately, but you can see it below the Stadium sign in this picture...


