HVAC Dust or Soot Stains

Diagnose Soot & Other Indoor Wall or Ceiling Stains
Traced to Heating or Air Conditioning Equipment
Stains at air supply registers

Don't Confuse Problematic Duct or Register Stains with Other Indoor IAQ Problems

The primary source of dark stains in this room is a problematic heating system in this photo courtesy of an InspectApedia reader discussed in this article's FAQs page linked at page bottom.

Our red arrows mark black soot stains that show the path of air leaving the ceiling register - soot is blowing trough this HVAC duct system.

But notice also that between our orange lines (marking the probable location of ceiling joists) we see a larger soot-stained area. I think that that's probably an area of poor or leaky ceiling insulation, causing a cooler ceiling surface that that picked up and held more of the dust blowing out of the nearby air supply register.

Notice that the area between the orange lines that is sooty is darker where closer to the air supply register.

Watch out: black sooty stains in your building might point to very dangerous heating system carbon monoxide hazards, particularly if your heat fuel is LP or natural gas.

We explain this hazard at GAS BURNER SOOT CAUSE & CURE 

Alternatively, such sooting from an oil fired heating system can tell us that there's an unsafe heat exchanger or an improperly-operating oil burner that risks a dangerous puffback explosion, as we explain

at OIL BURNER SOOT & PUFFBACKS

Be sure you have working CO Carbon Monoxide and Smoke Detectors in your building, then call your heating service company for help.

Don't confuse other indoor dark or sooty stains caused by air leaks or thermal tracking with stains that originate right at an HVAC system air supply registeer like those in our photo just above.

The stains in our page top photo and the photo just above are caused by the operation of the heating or air conditioning system without an air filter installed, by damaged, leaky, or contaminated ductwork, or by a serious dirt, dust, soot, or debris problem that is close to the return air inlet for these HVAC systems.

To compare these stains at air registers with other common indoor stains on walls and ceilings, see

THERMAL TRACKING BRIDGING GHOSTING

Dirt, Debris, Stains around Heating or Air Conditioning Air Registers

The soiling and "stains" around the ceiling supply register for warm air or air conditioned cool air show that the air system is dirty, has inadequate filtration, or is operating unsafely.

Here's what we see that strongly suggests that the primary source of dark stains in this room is a problematic heating system:

1. Black sooty stains are darkest right over the warm air supply register at the floor in the photo's lower right corner©
2. There are no stains or soot marks on the building walls where pictures have just been removed
3. Black sooty stains are less dark on the wall surface as we move higher on the wall away from the heating register
4. Black sooty stains on other walls in the room are much less noticeable

While mold or other problem particles could be present in this dirt or debris, if they are present they are coming from another source, not from this soiled area on the ceiling.

Here the debris deposited on the ceiling is in a common pattern where warm or cool air supply registers blow air across the ceiling surface (including from leaks around the perimeter of the register grille in this case.)

The stain pattern is from building air movement, it is not thermal tracking and it is not, by itself, an indicator of problem mold.

A lab test of this debris for the presence of mold would not be justified based only on the observation of these stains, but it might be justified if there were other reasons to need to screen the building or its HVAC system for problem mold or other contaminants.

If you have frequent fireplace fires, cooking, or if you burn scented candles, if people smoke

in your home, or if your oil-fired or gas-fired heating system is not working properly, the added soot particle load in the building air is not only a health concern (soot and potentially lead), it also will mark the building surfaces in this characteristic pattern.

You can see examples of this staining

at STAINS CANDLES FIREPLACE WOODSTOVE

We welcome more thermal tracking, soot tracking, air bypass leaks, and similar photos of indoor stains as well as text suggestions to expand this detail and would be glad to credit contributors.

Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations discussed in the remaining sections of this article.

Normal House Dust Deposits at a Heating or Air Conditioning Air Register

Above the light gray dust deposits at this heating air supply register look normal - that is, house dust, comprised principally of fabric fibers and skin cells is usually light gray in colour in such deposits.

Only by examination in a forensic lab will we know for sure what's in the dust on this register, but unless there is reason to suspect that there are contaminants in the system such testing is normally not appropriate.

See MOLD / ENVIRONMENTAL EXPERT, HIRE ?- when to hire an expert

Below is a close-up example showing typical light dust deposits on an air supply register.

The rust, depending on its cause and the source of moisture, might lead to a question of moisture, condensation, or perhaps mold contamination in the duct work of this building.