for some reason this year there has been a black film above the baseboard heater on the walls. Which washes off but is annoying.:eek: We have gas forced hot water system. I've never seen this before. It only appears above the baseboards in all the rooms. We recently had the furnance service by Gas company & we got a clean bill of health. We also have a CO detector in the bedroom & nothing is register on that. Could it be due to cold walls vs heater adhering dust.