Candles May Not Be The Cause Of Sooting

Ruling Out Mold and Candle Soot

In staining cases that are not clear-cut, mold may be suggested as the culprit in sooting stains. But, black sooting stains are easily distinguished from stains caused by mold growth. Although the area in which a stain appears could be sampled and cultured (see "Sampling Stains for Fun and Profit," HE Sept/Oct '98, p. 12), and the sample would probably grow a few mold colonies, mold can quickly be ruled out. First, mold growth can be many colors, including white, black, various shades of green, or pinkish brown. Second, the outer edges of mold stains will look fingerlike or feathery. In contrast, sooting stains will be grayish black and will have a more uniform outer edge.

It is more difficult to rule out candle soot or car exhaust as potential sources. However, my experience is that candles are rarely the cause of sooting stains. Heavy candle use can contribute to staining near the candles, but it does not typically cause soot stains throughout the house. Furthermore, in many of the cases of soot staining I have seen, the owners did not use candles except for special occasions such as Thanksgiving and birthdays, and the stains clearly came from a different source.

If you are still unsure of the source of a sooting stain, one place to go for help is a laboratory. A lab can use scanning electron microscopy to determine, for example, whether a stain is caused by deteriorating insulation or by candle soot. Particles in stains from insulation material are significantly larger than particles from candle soot. Another way a lab can spot the difference is by running a chemical analysis of the material, checking for the presence of chemicals released by insulation off-gassing and degradation.

But, the clearest indication that deteriorating insulation in the air handler is the source of sooting stains is the way the stains appear in the house.

Staining Patterns

Often the stains first appear on the walls and ceiling, particularly on exterior walls. They concentrate on inside surfaces along the ceiling joists and wall stud boards, and especially around nail heads, where the surface temperature is lower than the temperature in the surrounding area.

This pattern is similar to that seen in smoke damage after a fire, because similar forces are at work. Because of the billowing effect of smoke and the airstream in a fire, soot and ash tend to concentrate and be deposited first at the juncture between the ceiling and the wall. Impaction and attraction, together with gravity, are the main forces involved in this characteristic staining deposition. Stains also may outline furniture or other objects on the floor, and windows or pictures on the walls.

Impaction

Impaction is a physical force that plays a key role in particle deposition. The air in a building is fluid and moves through the occupied space in a distinct, usually circular, pattern. typically this is a pattern of convection, in which warm air rises in the middle of the room, cools while moving toward the walls, and falls again. When the air turns to go down a wall, some particles in the airstream, the larger ones, keep moving outward instead of down. Because of their larger size, and thus greater momentum, inertia keeps them moving in a straight line until something stops them and the particles impact on the wall's surface (see figure below).

Attractive Forces

The attractive forces include static charge and "thermophoresis." Static charges--and therefore, sooting stain depositions--often occur on the television screen, plastic pipes, plastic dishes, vinyl window and door casings, and plastic appliance cases. They are also often seen inside the refrigerator, especially on the egg-keeper and butter door. This is due to the fact that many plastic items have an electronic, or static, charge buildup on their surfaces because of the chemical nature of the material and the way the item is manufactured. Polyethylene and polypropylene are two plastics that typically build up static charges.

Static charge results when there is a an overall net possitive or net negative charge on the surface of an item. This happens when two surfaces are pressed tightly together and then pulled apart, or from friction. One of the surfaces will have more electrons (net negative) and the other will have more protons (net positive). You can also create ions from air molecules when the air is passed through an electric field or a magnetic field. A classic example of static charge is the "shock" a person gets when they touch a metal object. The person has "discharged" themselves with a micro-lightening strike.

Opposite charges attract whether it is the surface it was just removed from or a different surface. If you have a surface that is positivly charged and you have another surfac that is negatively charged, they tend to be attracted to each other. The result is a dirt accumulation on the other surface.

Thermophoresis, or "thermal precipitation," is a physical settling effect in which particulates in the air stream plate out on surfaces that are colder than the airstream. Different materials acquire or lose heat at different rates; therefore, some items will always be colder than other surrounding items. Particles will "stick" to colder surfaces and will become noticeable as a sooty stain.

Gravity

Soot staining often outlines such things as furniture, pictures, and window treatments, and may be found on the top side of ceiling fan blades when the fan is turned off--anywhere there may be a pocket of still air. This is because the still air allows the particulates time to drop down, pulled by the Earth's gravity, and settle on the closest surface.

http://www.homeenergy.org/798.stainsource.ruling.html

RE: candle soot!?!
Posted by: Christy - IA (christyh@netins.net) on Thu, May 27, 99 at 16:57

Don't be so sure it is candle soot. Do any of you have a new furnace by chance? The furnace could be the culprit, not the candles. We have a new furnace and soot - and are in the process of having the soot tested because an environmental specialist we contacted said "NO WAY IS THIS CANDLE SOOT". Of course, the furnace manufacturer says it is.

To make a really long story short, the environmental company says that many of the new furnaces that are being manufactured use a particular type of insulation in the furnace wall, the insulation fibers are being burned in the furnace, in turn the soot from those burnt fibers is what is showing up on homeowners walls.

The soot from the fibers leaves a specific residue that candle soot doesn't. There are some home owners on the East Coast that are sueing furnace manufacturers over this very issue.

RE: candle soot!?!
Posted by: Kenny C. (canserv@bellsouth.net) on Thu, Jun 3, 99 at 11:44

I attend seminars on IAQ and this has become a hot topic. It turns out there are many factors that affect the soot generation by candles and its ditribution by a heating or airconditioning system. This person may have a compounded problem due to air intake location, the type of filters used and any air leaks between the filter and the indoor unit. These are only a few things to consider. My first area to inspect is the connection between the filter and the unit, any leaks would cause unfiltered air to enter into the fan. For soot to come out of the supply grill the following path was traveled. The soot in the air went through a filter or around it, through the blower, past the heater, through the evaporator coil, through the supply plenum, through the supply duct, and lastly through the supply grill. While on this trip it stayed airborne and did not stick to any surface. This does happen, but the concentrations of soot are very high for very long periods of time. If the return air duct is air tight and a 40% pleated air filter is used I feel confident the system will not take in any soot.

RE: candle soot!?!
Posted by: Bill Drake (kj5zv@ix.netcom.com) on Thu, Jun 3, 99 at 11:44

I must agree with Marian about the insulation in furnaces. The portion of insulation around the heat exchanger is fiberglass with aluminum foil facing the air stream so that the insulation is encapsulated between the casing and the AL.foil. Some furnaces have insulation within the return air compartment. This is black matt faced designed by the insulation manufacturers just for such applications and has been used in the HVAC industry from the late 1970's. Like Marian said until the last two years in paticular, sooting was not an issue. It would therefore seem logical not to blame the insulation which has been used in the marketplace by HVAC units for many years.

Bill

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