It refers to streak-like markings (often referred to as ghosting) that can occur at interior stud locations on outside walls or where rafters / trusses are on vaulted / sloped ceilings. These streak-like markings may be as a result of soot (carbon), mould or dirt that collects there, as these locations are cooler (and “wetter”) than the adjacent insulated cavities. Because they are cooler, micro-condensation forms on the cold surface when heat reaches those locations. The resulting thermal telegraphing (or ghosting) occurs when particulate in the air such as dirt or soot (carbon) are deposited on those cooler surface locations.
Soot (carbon) staining can also occur along the perimeter of carpeted floors, in part because there is not a good air seal between the wall-floor juncture. Not all staining however may be caused by soot, as dust or dirt causes most marks on carpets and will wash out quite easily. Black carbon soot stains on the other hand are often permanent. Because the staining is dark by nature it’s most evident on light coloured carpets.
Ghosting or staining caused by carbon soot can come from inside or outside the house. Sources can include:
- automobile / airplane exhaust
- leaking combustion from fossil fuel appliances e.g. gas furnace, gas hot water heater, gas fireplace.
Carpets can act as filters for airborne particles. For example, if a door to a room is usually kept closed, pressure from a heat supply register in the room can force air underneath the door and trap particles in carpet fibres.
If you think you are experiencing ghosting or soot (carbon) staining, professional advice from an indoor air quality expert or licensed heating contractor to ascertain there is no spillage from gas appliances or sources detrimental to your health and safety is recommended.