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Stains around supply register


Jerry Simon
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Originally posted by Jerry Simon

What could cause this black, soot-like staining around a heating supply register? Gas forced air furnace, and the heat exchanger was a bit corroded, but otherwise okay. Thanks much.

Around here, I mostly see that when there's a nasty old oil furnace. On startup, the sucker belches out a puff of soot and the oily soot finds its way into the air stream.

Alternately it could be soot from candles or those smelly oil lamp thingys.

- Jim Katen, Oregon

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I see this all the time in commerical buildings and residential homes. I believe the cause of this is a dirty duct system and possiable the transfer of air from one area with a large amount of dirt and dust being put thru the system and not being filtered properly. Most of the time you will see this on high suplys and returns. This is my best guess.

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Each explanantion sounds quite feasible.

Ok, how's this for a possibility: The register doesn't fit the duct work properly and the cold air from the cooling season is being forced out, leaking around the register, chilling the wall surface and water in the air condenses and supports mold growth.

The register doesn't exhibit the growth because there's no food there for the mold.

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Originally posted by Chad Fabry

Each explanantion sounds quite feasible.

Ok, how's this for a possibility: The register doesn't fit the duct work properly and the cold air from the cooling season is being forced out, leaking around the register, chilling the wall surface and water in the air condenses and supports mold growth.

The register doesn't exhibit the growth because there's no food there for the mold.

You had me till you got to mold. I can see the cold air causing condensation. I can see dirt sticking to the condensation. But I've got a case of IPA that says it ain't mold.

- Jim Katen, Oregon

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Originally posted by Chad Fabry

Ok then, dirt.

I was just trying to think outside the box.

What's IPA. I'm pretty sure that whatever it is I'd be willing to buy a case and share it w/ you.

India Pale Ale

visit http://www.allaboutbeer.com/style/modern_ipa.html

and http://beeradvocate.com/beer/style/116/

- Jim Katen

"A fine beer may be judged with only one sip, but it's better to be thoroughly sure."

-Czech proverb

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I was in a CE class once and the presenter said stains like those were indicative of flue gases mixing with conditioned air and a failed heat exchanger. I remember thinking about pressure differentials and wondering if the guy had a clue what he was talking about.

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Originally posted by Bain

I was in a CE class once and the presenter said stains like those were indicative of flue gases mixing with conditioned air and a failed heat exchanger. I remember thinking about pressure differentials and wondering if the guy had a clue what he was talking about.

Sounds like BS.

If there's a small hole or crack in an oil furnace heat exchanger, the pressure is going the wrong way to get flue gases into the airstream.

If there's a honkin' big hole in the heat exchanger (not unusual if the refractory has failed) then you get so much flue gas into the airstream that there's little doubt about the problem; the whole house gets coated in an oily film of soot.

- Jim Katen, Oregon

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Originally posted by Jim Katen

Originally posted by Bain

I was in a CE class once and the presenter said stains like those were indicative of flue gases mixing with conditioned air and a failed heat exchanger. I remember thinking about pressure differentials and wondering if the guy had a clue what he was talking about.

Sounds like BS.

If there's a small hole or crack in an oil furnace heat exchanger, the pressure is going the wrong way to get flue gases into the airstream.

If there's a honkin' big hole in the heat exchanger (not unusual if the refractory has failed) then you get so much flue gas into the airstream that there's little doubt about the problem; the whole house gets coated in an oily film of soot.

- Jim Katen, Oregon

Jerry said it was a gas furnace in the home. As for the flue gases mixing with the house air stream, if the pressure differential around the entire heat exchanger always acted to preclude the admittance of combustion waste gases it seems to me that we wouldn't have to worry about carbon monoxide entering the home from a failed HE.

I do know that I have seen similar stains more than once in older homes which sport a brand new furnace at the time of the inspection, making it seem plausible that the staining was likely due to a bad HE in the previous furnace.

Without other clues, all I would know to do would be to try to rub some off and smell it. If it smells like Glade or Renuzit you've got your answer!

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Originally posted by AHI in AR

Originally posted by Jim Katen

Originally posted by Bain

I was in a CE class once and the presenter said stains like those were indicative of flue gases mixing with conditioned air and a failed heat exchanger. I remember thinking about pressure differentials and wondering if the guy had a clue what he was talking about.

Sounds like BS.

If there's a small hole or crack in an oil furnace heat exchanger, the pressure is going the wrong way to get flue gases into the airstream.

If there's a honkin' big hole in the heat exchanger (not unusual if the refractory has failed) then you get so much flue gas into the airstream that there's little doubt about the problem; the whole house gets coated in an oily film of soot.

- Jim Katen, Oregon

Jerry said it was a gas furnace in the home.

At this point in the conversation, I was responding to John's story about a CE instructor. I presume that the instructor was talking about oil furnaces because gas furnaces don't normally produce much in the way of soot. (Well, they can, but they’ve got to be seriously screwed up to do so.)

As for the flue gases mixing with the house air stream, if the pressure differential around the entire heat exchanger always acted to preclude the admittance of combustion waste gases it seems to me that we wouldn't have to worry about carbon monoxide entering the home from a failed HE.

Well, for the great majority of cases, there's little risk of CO entering the home from a failed HE. It can happen with a large hole and it can happen during the purge cycles, but in most cases the household air moves out through the crack, the exhaust gases don't move in. If a furnace is going to contribute CO to the household air, it's almost always going to do it because of problems with the vent, not a crack in the HE.

I do know that I have seen similar stains more than once in older homes which sport a brand new furnace at the time of the inspection, making it seem plausible that the staining was likely due to a bad HE in the previous furnace.

Or maybe it had nothing to do with the HE. The black stuff is dirt. It could come from soot, cigarettes, candles, oil lamps -- lots of things. As far as I can tell, a busted HE is way down on the list of possibilities.

Without other clues, all I would know to do would be to try to rub some off and smell it. If it smells like Glade or Renuzit you've got your answer!

Not a bad idea. I'll try it next time.

- Jim Katen, Oregon

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I've heard those marks described, maybe here, as "ghosting". The friction of the supply air makes the wall surface magnetically attractive for whatever is in the air, maybe in the air stream, maybe just in the ambient room.

I have definitely seen similar effect where kerosene heaters were used in a room, spewing out their load of effluent trash.

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Originally posted by Jim Katen

Originally posted by AHI in AR

Originally posted by Jim Katen

Originally posted by Bain

I was in a CE class once and the presenter said stains like those were indicative of flue gases mixing with conditioned air and a failed heat exchanger. I remember thinking about pressure differentials and wondering if the guy had a clue what he was talking about.

Sounds like BS.

If there's a small hole or crack in an oil furnace heat exchanger, the pressure is going the wrong way to get flue gases into the airstream.

If there's a honkin' big hole in the heat exchanger (not unusual if the refractory has failed) then you get so much flue gas into the airstream that there's little doubt about the problem; the whole house gets coated in an oily film of soot.

- Jim Katen, Oregon

Jerry said it was a gas furnace in the home.

At this point in the conversation, I was responding to John's story about a CE instructor. I presume that the instructor was talking about oil furnaces because gas furnaces don't normally produce much in the way of soot. (Well, they can, but they’ve got to be seriously screwed up to do so.)

As for the flue gases mixing with the house air stream, if the pressure differential around the entire heat exchanger always acted to preclude the admittance of combustion waste gases it seems to me that we wouldn't have to worry about carbon monoxide entering the home from a failed HE.

Well, for the great majority of cases, there's little risk of CO entering the home from a failed HE. It can happen with a large hole and it can happen during the purge cycles, but in most cases the household air moves out through the crack, the exhaust gases don't move in. If a furnace is going to contribute CO to the household air, it's almost always going to do it because of problems with the vent, not a crack in the HE.

I do know that I have seen similar stains more than once in older homes which sport a brand new furnace at the time of the inspection, making it seem plausible that the staining was likely due to a bad HE in the previous furnace.

Or maybe it had nothing to do with the HE. The black stuff is dirt. It could come from soot, cigarettes, candles, oil lamps -- lots of things. As far as I can tell, a busted HE is way down on the list of possibilities.

Without other clues, all I would know to do would be to try to rub some off and smell it. If it smells like Glade or Renuzit you've got your answer!

Not a bad idea. I'll try it next time.

- Jim Katen, Oregon

Fair enough...but I still say that a bad HE can cause that kind of staining. I didn't say it was definite. Keep in mind that all we have to go on is a brief description; I'm just throwing out possibilities like the others -- not guaranteed answers by any means. I would agree that it is most likely just dirt from a poorly filtered system. That was posited first. But we don't know if the filter was dirty, or missing, or if there was a heavy cigarette smell, or an excess of candles or oil burning thingies. (My spelling)

Imagine this scenario: you have incomplete combustion for whatever reason(s) AND a bad HE. Lovely, fall-like orange colors above your burners. Prior to the start of the blower, your burners are emitting crap which can be pushed into the duct system. Air pressure is working against Harry Homeowner at this point since there is no pressurized flow around the HE. If this goes on for a few years, I can imagine some sooting could occur through the ducts.

It may be a long shot, and I may have been assuming too much from one photo, but the door casing appears to be the old "clamshell" style. That hasn't been in common use since the mid 1960's. Not around here, anyway. If that's the case where the photo was taken, this home could have had a couple of furnaces which were ignored and left in service past the point where there were problems.

Just a guess. May be totally wrong. But then, I'm not getting paid, so it's OK in my book...

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Originally posted by AHI in AR

Fair enough...but I still say that a bad HE can cause that kind of staining. I didn't say it was definite. Keep in mind that all we have to go on is a brief description; I'm just throwing out possibilities like the others -- not guaranteed answers by any means. I would agree that it is most likely just dirt from a poorly filtered system. That was posited first. But we don't know if the filter was dirty, or missing, or if there was a heavy cigarette smell, or an excess of candles or oil burning thingies. (My spelling)

Imagine this scenario: you have incomplete combustion for whatever reason(s) AND a bad HE. Lovely, fall-like orange colors above your burners. Prior to the start of the blower, your burners are emitting crap which can be pushed into the duct system. Air pressure is working against Harry Homeowner at this point since there is no pressurized flow around the HE. If this goes on for a few years, I can imagine some sooting could occur through the ducts.

It may be a long shot, and I may have been assuming too much from one photo, but the door casing appears to be the old "clamshell" style. That hasn't been in common use since the mid 1960's. Not around here, anyway. If that's the case where the photo was taken, this home could have had a couple of furnaces which were ignored and left in service past the point where there were problems.

Just a guess. May be totally wrong. But then, I'm not getting paid, so it's OK in my book...

I like the way you construct your argument. It's persuasive. I agree that your scenario is possible.

- Jim Katen, Oregon

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I'm just finishing up a complete gut and reconstruction of a hi-rise condo in Manhattan. I installed central air into the apartment. Within a few weeks, similar staining was visible around numerous ducts. Especially in areas where I hand alot of dusty work going on.

The HVAC contractor explained that it was simply dust and dirt in the air. He actually stated that it showed him that his system was working. Something to do with the air currents picking up the dirt in the air. He assured me once we were finished with the "dirty"work, and cleaned it up, the problem would disappear. We did, it has and he was right.

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Concerning AHI's theory.

One thing that must be considered is that since we're pushing air across the heat exchanger vortexes are created and a low pressure area exists in locations around the heat exchanger, especially on the air exit end, but also on the inside of corners.

The same effect cause the backside of vehicles to be dirty. It's entirely possible to draw exhaust gas into the circulated airstream. It's the most likely thing but certainly possible depending on where the exchanger failed.

I've drawn a picture but my scanner keeps rejecting crayon.

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Put me in the "ghosting" camp. The source of the soot/dirt/dust could be from the furnace, or any other combustion appliance in the home, or from a fireplace, or incense, or candles, or be passing through the vacuum cleaner bag, etc. It could just be floating in the air in the room and doesn't need to have traveled through the duct to get there.

There are three known forces that cause the dirt floating around in the air to be deposited in a particular location: impaction due to air flow, gravity, or attraction (usually due to electrostatic charge or moisture). I think we could rule out gravity on this one but the other two types of forces are clearly in play here.

Assuming I've gone through the inspection and didn't find problems with the combustion appliances or their vent systems, I'd do what Walter recommended -- clean it off and see if it came back.

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Like WJ says, just wipe it off. The system that I mentioned above Was central air... no heat. The original stain occured after a few weeks of a dirty enviorment, Now that it's cleaned up, it has been about two months without a reoccurance.

Another example that the HVAC contractor gave me was that he stated you usually don't see it in a house, because the air is reletively clean. But look at the ducts in places like supermarkets with dropped ceilings and ceiling registers and you will begin to notice the stains.

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Originally posted by Chad Fabry

The register doesn't exhibit the growth because there's no food there for the mold.

Actually there is food in most registers for mold growth. Yes, mold requires organics for food and where would it get it?

Has anyone heard that you should replace your matress at least every 10 years and then it will weigh ~ twice what it did when it was new. What could make a matress heavier?????

Skin cells, dander, etc. Why should you only lose skin cells when in bed? They are sloughed off continually, 24hrs/day, 7 days a week. Surely you don't think that that fiberglass spun filter will filter out the cells. They will settle out wherever they can, including inthe ducts, fan case, plenum, etc.

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My guess is ghosting. Cooler air from the A/C combined with higher humidity in the home and you get condensation . The heavier areas may be where the grill leaks more at the edges and blows the cold air across the surface of the drywall. A/C shuts down and moisture condenses on the cooler areas of the drywall which in turn makes a nice area for dust, candle soot, etc. to stick to. Notice that the track above the grill also has stains and there are new ceiling tiles.

This would be the same circumstances that allows you to see every ceiling joist on a cathedral ceiling with no thermal break.

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Well I'm not sure about all that high tech stuff. My 2 cents worth. It looks to me like leaky duct work in the attic causing a low pressure condition in the home interior. I test ducts leaking 200-400 cfm all the time. That along with poor sheetrock cutting that leaves a gap between the register and the ceiling/wall provides a perfect makeup air path. The air is very dirty after passing thru loose fill insulation in the attic. Notice the stain appears to be emanating from under the grill.

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