I'm looking to purchase a home that has a hot water system. This home shows black marks above the radiators on the painted walls. What does this mean and should I be concerned? The previous owner was a smoker could it be residue or is it another more serious problem?
Can you post pictures? Are the radiators for sure hot water or could they be steam?
Sometimes in homes with heavy smokers, the air flow patterns over the radiator fins are so consistent that the smoke residue collects in those places where the air passes over the exact same spots on the walls for years on end. I've never seen black though, it's usually just a brownish discoloration. Black implies soot. Hot water can't get hot enough to make soot, but steam can and that would indicate a serious problem.
Heat rises and dust goes with it. Dust gets deposited in vertical lines above the radiators over yeas. I see it often in houses where the occupants are, less than, let's say, tidy. No offense but hot water boilers can definitely make soot with any fuel but oil fired takes the cake. Anything burning fuel rich will make soot. Soot is just unburnt carbon from incomplete combustion.