Puzzled by duct cleaning

We had some smoke/soot damage in our house in the recent SoCa wildfires.
Our insurers (State Farm) had the interior of the house cleaned and washed by professional cleaners.
After they cleaned the house, they had a commercial duct cleaning outfit (Airtek) clean the heating ducts.
A few hours after they had cleaned the ducts, we noticed an unsightly layer of black, gritty soot coming out of our heating vents. It was noticeable on paper that had been lying on the floor under the vents.
Airtek has been back four times and kept cleaning the ducts, and still there is soot coming our of the vents. Now there is less gritty soot coming out, but more small patches of thin plastic overlaid with soot.
Any ideas what the problem might be?
--
Walter
www.rationality.net
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Cduct cleaning probably isn't effective and you may have to replace.

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wrote:

Just ask your insurance to build you a new house so that all in your life is absolutely perfect once again.
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He doesn't need a new house! It survived the So Ca wildfires.
OP, might need to replace ducts, if any heat damages. I would think after four visits back the duct cleaners; insurance company would wise up.
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What are the ducts made of? If ductboard and/or flex, they should be replaced. Actually should have been replaced from the start and been done with it. If they are sheet metal, they should be able to be cleaned. What is the outfit using to clean them? I don't know about the company you have now, but there are some so called duct cleaning outfits here that piddle around with a little glorified shop vac -- talked to several people that said "Hell, I could have done what they did myself." Need more info to make any more suggestions Larry PS, an afterthought== sheet metal that is insulated inside will probably have to be replaced also. I was thinking of sheet metal insulated outside.
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I have black soot coming out my ducts too. In fact, the vents in my white ceiling and wall have to be cleaned periodically to remove the black soot.
But there has been no fire anywhere near me. Ducts tend to pick up soot and redistribute it in a concentrated area because they move so much volume of air.
In addition to what you have on all the items in your home, when you open your doors, you are letting in a tremendous amount of 'soot' that is run thru your duct system. Also molds and all the million of bacteria and germs you see on tv commercial.
wrote:

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Sound like the burner flame is not combusting completely. A red or yellow flame indicates free carbon formed. Make a note if the furnace walls next to the burners are sooty. Sit by the furnace when it comes on and take a good look until it shuts off. Its fairly easy to adjust the air/gas mixure yourself until you get a hot blue flame. Remember the bunsen burner in high school lab?
I am winging it here. The burner combustion gases should go straight up the flue and never get into the heated air circulation. Else you would get carbon monoxide poisoning. Do make your own observations as to whether you feel nauseous or "not that good" when the furnace come on. Don't let your imagination get the better of you. But its a precaution worth taking.
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