Walters Forensic Logo  Publications Contact Us Home 


Unless you live in a house that has the air treatment systems and seals of a Class IV Biohazard Containment Facility, you will have "dirt" in your house. This normally does not result in a claim against the homeowner's insurance policy. However, in cases of extreme dirt buildup in a house, claims can result. We have investigated a number of these situations, where the source of the dirt is unknown.

Abnormal and excessive buildups of dirt can occur for a variety of reasons including the following; soot from the burning of large quantities of candles and/or oil lamp, soot from cracked heat exchangers on furnaces, soot from blowback on fireplaces as a result of blocked chimney or improper chimney or vent installation/instruction; the list goes on.

You will note a theme in all of the aforementioned reasons: soot. Soot is a product of incomplete combustion of carbonaceous fuel, and contains carbon and is dark grey to black in colour. We were called to a house recently where the homeowner had claimed for cleaning and related costs which were incurred due to what we were told was excess "soot". According to the homeowner and the insurance adjuster, the walls and contents had been covered in "soot" (we were called in after the "soot" had been removed). They had just moved into the brand new house at the end of the summer, and noted the "soot" in the house around mid November. Consumers' Gas were called in and determined that the furnace heat exchanger was not cracked (which can also cause carbon monoxide (CO) to enter the house with lethal consequences). Thus we were called to investigate. The unusual suspects were rounded up and checked out (chimneys, vents, furnace heat exchangers, candles, etc.), but were ruled out as being the cause of the "soot".

By now, you may be asking - why is soot in quotation marks? - Because the dirt in the house was not soot! Everyone assumed that the excess dirt in the house was a product of combustion, or soot - we determined otherwise. One area which had not yet been cleaned was the furnace. We removed some sample dirt from this area, and noted that it was a medium grey colour, felt "greasy" to the touch, had no odour of combustion, and no visible presence of carbon. Thus we determined that the dirt was not soot.

If it wasn't soot, then where was the dirt coming from? We recalled the homeowner's comment that, during Consumers Gas' investigation of the furnace, it was found that the electronic air cleaner had been installed backwards. The installer was called back, at that time, corrected the installation, and commented that it would not have created dirt in the house. As it turns out, the installer was correct: the improperly installed electronic air cleaner did not create dirt in the house, but it did cause existing dirt in the house to behave differently.

Our examination of the furnace blower and electronic air cleaner revealed that, upstream of the air cleaner, the ductwork was relatively clean. Downstream however, was filthy. This observation suggested that something was happening at the air cleaner, as the cleanest portion of the heating system should have been downstream of the sir cleaner, but it wasn't. A call to the manufacturer of the electronic air cleaner verified our suspicions: the air cleaner, when installed backwards, could cause the dust particles to become positively charged and be released back into the house. Such charged dust particles would stick to themselves and to any surface they would come into contact with.

In a proper installation, as shown in the sketch, the dust particles are drawn over the charging wires in the electronic air cleaner, where they are given a positive electrical charge. The dust particles then pass over the collector plates, which are of the opposite (negative) charge, and stick to the collector plates, thus the air is "cleaned". When the air cleaner is installed backwards, the dust particles pass over the collector plates first, and don't stick, as they have not yet received a charge from the charging wires. They then pass over the charging wires, are positively charged, and continue into the furnace, where some of them adhere to the ductwork, blower, etc. The rest are released back into the house through the heating ducts. Once back into the open spaces of the house, the positive charge on the dust particles causes them to settle out of the air more quickly. So, the air in the house likely was cleaner than if there was no air cleaner present. Unfortunately, everything else in the house was dirtier as a result!

We recently followed up with the homeowner, who reported that the problem had not reappeared since the air cleaner was properly reinstalled. We understand that subrogation against the air cleaner installer is being considered.

So even when it appears that the mystery of your situation may never be solved, don't give up, just give us a call.

The information contained in this web site is intended for marketing purposes only. It is not all-inclusive, and does not fully describe the many and varied services that the company provides, nor does it completely describe the education, training, skills, or expertise of our staff.


Walters Forensic Engineering | 277 Wellington Street West, Suite 800 | Toronto, ON M5V 3H2
Information contact: