Lightning wrote: titleist1 wrote:By any chance is the black on the walls a ghost image of the wall studs?
I don't understand how this could relate..
If he is getting thermal bridging via the outside wall studs the temp difference there will attract dirt and show up as black shadows on the walls matching their pattern. Especially if there may be a little extra soot from burning bit coal not hot enough and opening the loading door a little too long loading it back up. Or if burning some candles or oil lamps frequently (our one bathroom has this tendency because the spousal unit likes candles in there occasionally - I prefer to just blame the dog). It could especially show up in a back bedroom that may be cooler since it is further from the warmth of the stove.
I wasn't clear on how covered the walls were with the black, a pic would be real helpful.