Dark areas of carpet

[Reis Pearson]

I was in a house today and noticed dark edges on the carpet. The furnace seems to be operating fine, but something feels funny. I seem to recall in a training course something about the darking of carpet may be an indication of ??incomplete combustion?? or something... Does this sound familiar to anyone?:confused:

[Matt Fellman]

From what I've seen it's around edges of the carpet where air is passing into the house. It's the result of a negative pressure in the house which can happen for a variety or reasons, some normal some not.

For instance, you turn on a bath fan and it moves air out of the house. That air has to be replaced somehow. Often the path of least resistance is through a seam by the baseboard which comes from the crawl space. The carpet is acting as a filter of sorts, thus the discoloration.

You can also have negative pressure if there is a leaking or detached heating duct that is taking air from the hvac system and putting outside the living space of the house. Again, the air has to be made up somehow.

It's usually more noticeable on lighter color carpeting. When I see it really heavy it makes my radar go up a bit to look for a detached heating duct somewhere. It's not a for sure but it often the case. Also, if the occupants of the house just cook a lot and have a powerful vent fan it can cause a lot of air passage from the outside.

This is also what often causes a fireplace to smoke.

As houses get more air tight this stuff becomes more common. There was a guy at a CE class that I attended a couple years back that had a great talk about this stuff.

[David Banks]

Try this also.
BSD-150: Black Stains on Carpets and Ghosting of Framing — (http://www.buildingscience.com/documents/digests/bsd-150-black-stains-on-carpets-and-ghosting-of-framing/view?searchterm=Ghosting)

[Scott Patterson]

Whenever I see dark areas around the baseboards, doors, etc., I start looking for and counting candles. It has been my experience that when I find dark areas on the carpet along the walls that I will also find several candles in the home. This is not to discount a fireplace with or without gas logs that might also be adding to the problem.

[Rick Hurst]

Don't count out also it could be staining left behind from Pest Control chemicals. Some of the wettable powders used for ant, roaches and general pests will leave such a residue or staining if the PC tech is what we call a "baseboard jockey". That is someone who just goes in and fan sprays all the baseboards throughout the home.

[Richard Rushing]

Sometimes it's acchums razor-- the simpliest answer is the correct one.

Alot of times it is where the carpet will be waaay past it's prime and for years it hasn't been vaccuumed with a cleaner that does not have enough power to pull the dirt away from the baseboards. Additionally, the folks have only vaccuumed and not done the full-carpet cleaning for quite some time...

The HVAC system is a huge contributor to this staining if the conditions are right/wrong.

Not enough return air also will suck doors shut and draw contaniments from the fireplace. There are just alot of different things that could be happening here.

RR

[Jim Zborowski]

Along withh excessive candles, see how many of those " plug-ins" there are. They are usually a parafin or oil based product which end upcoating everything.

[Bob Harper]

Carpet soiling lines are usually formed by filtration of particulates due to forced air imbalances in the presence of particles.

First the particulates: I've posted on this before many times but you need to ascertain what is causing the particulates. Is it hydrocarbon soot, mold, soiling, etc. If it is hydrocarbon soot, is it from short chain aliphatic alkanes such as NG and LPG or is it from long chain alkanes such as solid or liquid fuels such as heating oil, diesel fuel, cooking oils, parrafins, or wax? It may take PLM with GC/MS to determine just what it is.

Next, what is the mode of trasmission? If you see black lines under a bedroom door and along the interior partition, it probably indicates the lack of a proper return in the bedroom or too much supply for the return. Also, large returns in the hallway can suck air right under wall plates causing room air to filter through the carpet. I've seen 4x8ft patterns in the carpet right above the furnace room. Sucking air right through the seams in the subfloor to get back to the furnace.

The bottom line is, while candles account for > 80% of the soiling cases I've handled, you don't know until you test.

Bob

[Jim Robinson]

Richard, I was going to correct your spelling of Ockham's, but then I googled it and realized you can spell it Ockham or Occam. I only know about Ockham's Razor because it was a band that I listened to a long time ago. Without that, I would have had no idea what you were talking about, and I still don't know what it means.

[John Arnold]

Occam's razor, also called law of economy, or law of parsimony, principle stated by William of Ockham (1285–1347/49), a scholastic, that Pluralitas non est ponenda sine necessitate; “Plurality should not be posited without necessity.” The principle gives precedence to simplicity; of two competing theories, the simplest explanation of an entity is to be preferred.

from Britannica Online

[Reis Pearson]

Pardon the ingnorance... What is PLM with GC/MS?
Thanks...


Carpet soiling lines are usually formed by filtration of particulates due to forced air imbalances in the presence of particles.

First the particulates: I've posted on this before many times but you need to ascertain what is causing the particulates. Is it hydrocarbon soot, mold, soiling, etc. If it is hydrocarbon soot, is it from short chain aliphatic alkanes such as NG and LPG or is it from long chain alkanes such as solid or liquid fuels such as heating oil, diesel fuel, cooking oils, parrafins, or wax? It may take PLM with GC/MS to determine just what it is.

Next, what is the mode of trasmission? If you see black lines under a bedroom door and along the interior partition, it probably indicates the lack of a proper return in the bedroom or too much supply for the return. Also, large returns in the hallway can suck air right under wall plates causing room air to filter through the carpet. I've seen 4x8ft patterns in the carpet right above the furnace room. Sucking air right through the seams in the subfloor to get back to the furnace.

The bottom line is, while candles account for > 80% of the soiling cases I've handled, you don't know until you test.

Bob

[John Arnold]

Pardon the ingnorance... What is PLM with GC/MS?
Thanks...

Don't feel bad. You're not the first to read a Bob Harper post and feel ignorant.

[Bob Harper]

Polarized Light Microscopy and gas chromatography with mass spectrometry.

The PLM determines the morphology of the particulate, which is compared with a catalogue of known materials. This can often rule out certain compounds. In the case with alledged soot or as we like to refer to it, "black particulate matter', if the sample does not disperse when probed but smears and contains yellow, it is clearly not from a short chained aliphatic hydrocarbon such as NG or LP gas, which is often as far as I need to go. For those cases where the particulate is mixed to where the PLM in inconclusive, the GC/ Mass Spec. will identify the exact compounds contained in it. This is cross-checked with an index to identify the material beyond a doubt. For instance, one case I investigated involved a LP gas ventfree stove in a home where the oil fired furnace and DHW heater both had extensive problems including adding makeup air due to the confined space. I just knew it was oil soot inhaled through duct leaks. Nope, it was vegetable cooking oil. Not just any oil but soybean cooking oil. They were into popcorn and ethnic stir frying. The fat was aerosolized and spread all over the house. Once it plated out on the windows, dirt attached to the mess making it visible. The stigmasterol spike in the gc/ms proved it was from soybeans.

I've seen THC from Left Hand cigarettes, charred food particles, mold from nearby crops, metal filings from door hinges, burned sawdust from remodeling with a dull blade---all sorts of fun stuff.

HTH,
Bob

[Matthew Skowron]

if it backs up to a bath room it could be a trim nail or sheet rock screw in a vent pipe that rusted away,and is allowing gas/water to soak into the sheetrockthen down into the carpet. I have seen this before, not as in-depth as above but worth a look.