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Black soot from gas heat baseboards

crandall249 Member Posts: 1

I paid 16 k for new Weil McLein gas furnace and hot water unit (they connect) 18 mos ago. Black soot is all over walls and above baseboards and in covers. Painted and 3 mos later it’s filthy. Carbon meters don’t go off and had someone here to measure carbon also. Why is this happening?


  • Long Beach Ed
    Long Beach Ed Member Posts: 1,213
    edited April 24

    You have some dirty combustion somewhere in the house, or a leak in a flue. Check every source of combustion - boiler, oven, dryer, stove, candles, etc. Check chimney and vent flues. Do professional combustion tests with instruments, not merely carbon monoxide readings. Was the boiler's burner properly set up using a combustion analysis?

    If they all check out, it can simply be household dust, carried through the convectors that are hotter than they used to be. If that's the case, try turning down the heating water temperature. That will reduce the air (and dust) flow somewhat.

    In the words of EBEBRATT, who is exceedingly smarter than I: "It is normal for any duct and dirt to get in the air current and get on the walls above any type of heater. But that may be more than dust or dirt."

  • pecmsg
    pecmsg Member Posts: 4,909

    I ASSUME Carbon meter is a CO detector,

    I agree with @Long Beach Ed and strongly advise getting a "Low Level CO Detector" Store bought CO detectors will not alarm until 70 PPM is reached and exceeded for up to 3 hours.

    The Defender low level CO detector is 1 model there are others.

  • Mustangman
    Mustangman Member Posts: 113

    Wow thats bad. I have seen this condition a few times. One house had a lot dirt inside the fin. It cooked the dust and showed up on the walls and the room corners. Your pic indicate to me that dirt is probably not the answer. Get a CO detector immediately and put it near the boiler.

    Are you getting light headed? Headaches? nausea? These are the first signs of CO poisoning. I ran into a situation very similar to yours. I got an over heating call on a brand new boiler. I walked in and just felt someting was wrong. The Old lady living there was sitting on a chair sleeping or so I thought. Her grandson lived with her also and he took me down. I went to the boiler and saw it was piped incorrectly. They put a flow check on the supply and used it as a tee to feed 2 zones. No joke. Im thinking OMG no wonder it over heats. I got a funny taste in my mouth while I was there. I have a habit of pulling the tee cap off the flue inspection tee ( I do it all the time ) I couldnt see anything.. just black. I noticed that the flue pipe had this tan color substance that looked like ice, right where it connects to the chimney. Told my son to take the flue off. The chimney was totally plugged. The installer connected the boiler to a chimney that was unlined. The chimney was crumbling down inside the chimney and all the pieces of brick and terra cotta fell down and plugged the chimney. My thoughts went to the old lady sleeping upstairs. We couldn't get her to wake up. Called 911 they came and gave her oxygen and she woke up. Her grandson had signs of CO poisoning.. both were hospitalized. Along with the pieces was this tan ice. We had to use a digging bar to break it up and clean it. The boiler was less than 2 years old. We fixed the boiler and cleaned the chimney. It has a liner in it now.

    The first place to look when ever you think CO is in the space is check the chimney base. I don't know how mechanical you are but taking the smoke pipe off WITH POWER OFF is pretty easy.

    Any boiler or furnace that vents into a chimney that is exposed to the outdoor conditions gets a liner or we include a price for steeple jack to install the liner. Everyone wants to know why now? The more efficient furnace and boilers have very low stack temperatures compared to many years ago. The flue gasses hit their dew point inside the chimney and condensate like crazy. You guys know that condensate from combustion is very acidic. I have seen more than once pieces of terra cotta in the chimney base.

    If you have an inspection tee… take a peek.


  • captainco
    captainco Member Posts: 796

    If you have done any other remodeling, this is a possibility

  • DCContrarian
    DCContrarian Member Posts: 200

    This article covers it:


    You have soot getting into your air somehow. When air is heated and then cooled the soot drops out. So it's accumulating over the radiators. The radiators aren't the problem. You need to find the source of the soot.

    flat_twinLong Beach Ed
  • clammy
    clammy Member Posts: 3,113

    What temp setting on the aquastat? I 've seen this on jobs that where they piped all supply and returns in 1/2 tubing and ran w the aquastat set to 200-210 to get enough output out of the baseboard the result was usually lack ghosting stains on the walls . Most seem to have been done in the late 70 s possible in a effort to cut costs being no one thought about all the ill effects of running high water temps last of which would be wall staining . i had a ocd customer and was a friend who had the issue ,he used a stain cover then primed and painted removed all carpet so possible off gasses from the carpet wasn t the issue and yet it reappeared . i lowered the aquastat to 180 and they didn't come back after repainting but when temps dropped the baseboard could not keep up . Repiped it in 3/4 and ran at 180 and that was it , Check the aquastat setting and also take a look at the t % p gauge on the boiler you could have a out of calibration mechanical aquastat . also would there happen to be any un condition space above like a knee wall ,attics are a different and insulation of should be checked and possibly added to . Not to add alot more but thermal migration from above uninsulated knee will increase convection on that wall and thus through the element and at high temps increase the chances of ghosting .Don't rule out indoor air quality as others have suggested CO, CO2 and humidity .

    peace and good luck clammy

    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    Long Beach Edkcoppjringel
  • hot_rod
    hot_rod Member Posts: 22,353
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kmt803
    kmt803 Member Posts: 1

    my sisters house had this , after some research I found it was something called “drywall ghosting” it was mostly on ceiling, adding more insulation fixed the issue.

  • propmanage
    propmanage Member Posts: 17

    Your new system is nice and hot, and you have old dust under your wall covers.

    Could be from anything even vacuuming or not using heat for a while.

    That’s dust heating up and rising.

    Needs a good cleaning and now a good painting.

  • JohnFX
    JohnFX Member Posts: 7

    I've seen this a few times as a rep for a boiler company. Lawsuits were threatened and concerns about health and safety were raging. But, as a few others here have mentioned, it is most likely dust picked up by high temperature baseboard (like 200f-210f).

    There was one occasion where it turned out to be scented candles.

    Dave in QCA
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,218

    My vote for house dust and/or air leakage at the base of the wall ( no one ever properly seals drywall, so the air leakage is considerable). The convection current from the baseboards pulling air up from the floor and/or through the leaks at the base of the wall also pulls dust. Poorly insulated outside walls will tend to be cold and somewhat moist, attracting dirt to collect on the walls. Seen this many times.

    REducing convection current by reducing water temperature, sealing up the home properly, making sure humidity matches the insulation level of the home to keep walls dry will probably all help eleiminate this problem.

    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • ridiculous
    ridiculous Member Posts: 1

    Are there candles being burned? Scented oil lamps? Glade plug-ins in outlets? In my experience, all 3 of these leave soot tracking when overused- google ghosting, candle soot. in really dramatic messes. you can see the outline of the studs in exterior walls. Also plastic surfaces, like TV's, insides of fridges, etc. will show residue

    Dave in QCA
  • Dyingtofly
    Dyingtofly Member Posts: 4

    Long Beach Ed and Mustangman, Steve have some astute observations. Though your boiler is fairly new, you may really want to pull the stack and check the chimney. I too have seen collapsed brick & mortar chimneys and for sure, the blockage may be up inside and not just at the base. That's why it's critical to check thoroughly. Your pictures seem to show upper corners of the walls and also significant staining on some wall areas that, as one commentator mentioned, appear to show an outline of the lumber framing. While I might suppose there could be an over-temperature issue of the water, I'm really suspicious of the integrity of the flue. It's a pretty easy check. Keep us all posted on what you find.

    Wishing you all the best!

  • tim smith
    tim smith Member Posts: 2,770

    i have seen this on many jobs with baseboard radiators. I would still err on the side of caution and make sure you have operational CO detectors. But most likely its just dust traveling by means of convection up the wall to corner of wall and ceiling convection. Dust and dirt in air once accumulated is darker in color.

    Good Luck


  • Larry Weingarten
    Larry Weingarten Member Posts: 3,356

    Hi, Maybe this will be of some use: https://inspectapedia.com/interiors/Thermal_Tracking.php

    Yours, Larry

  • Bob Harper
    Bob Harper Member Posts: 1,044

    If you search this site you will find this discussion in numerous places. I'll toss in a little: You do not know it is 'soot' without a proper lab test. It is, therefore, legally speaking, Black Particulate Matter. The convective air .movement from the rads along with plating out on a cold wall accounts for why the material is ending up there. The question is, what is it? This will lead you to the next question of where it is coming from, which then leads to the solution. For instance, most samples I've had analyzed contain a blend of dirt, dead skin cells, pet dander, mold, metal filings from door hinges, nicotine, carbonaceous charred food particulates, and, various types of 'soot'. You can have 'soot' from cellulosic materials, such as wood, paper, cigarettes, incense, etc. and you can have aliphatic hydrocarbon 'soot'. Within this spectrum, you can have short chain aliphatic soot, such as from NG or LPG then you can have a totally different type from long chain aliphatics, such as diesel/ heating oil, cooking oil, wax scents and candles. Jar candles are the worst because they suffer from a reduced O2 supply resulting in incomplete combustion.

    This is an insurable loss when it is "sudden and accidental within 12 months. You can get your insurance company to waive the magic wand and fix it then they can conduct this research and subrogate against the suspected offender. Don't clean or paint if you're going this route.

    As for combustion equipment, ALL of it should undergo combustion analysis and a Worst Case Depressurization Test. Get a low level unlisted CO monitor.


    Larry Weingarten
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited May 3

    Somehow I thought I already answered this, however the post I am referring to was on a different discussion of the same problem.

    Daughter's room? Not really, just an exaggeration for the daughter's room

    But I thought Jim Davis' - 2016 article "Black Soot Syndrome" posted by @captainco above was very interesting.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?