Sooty oil fired heating equipment: this article explains the significance of soot on, around, or inside oil fired heating boilers, furnaces, and water heaters.

We explain how much oil burner soot is normal and when soot production is a problem. Thick soot build-up inside of a flue, the chimney, or inside of the boiler or furnace heat exchanger or inside of a domestic water heater is a problem that causes higher fuel bills, equipment operating problems, and potential fire and safety problems.

How Soot Causes Problems with Heating Boilers, Furnaces, Water Heaters

These questions and answers were posted originally

at SOOT on OIL FIRED HEATING EQUIPMENT - be sure to review the diagnosis and repair suggestions that begin there.

Watch out: Safety warning about soot: Sooting can occur with both gas fired and oil fired systems.

Soot coming from a gas fired heater is probably indicating a very dangerous condition risking carbon monoxide poisoning.

If a gas fired appliance is producing soot, it should be turned off and Immediate service is needed.

Soot coming from an oil fired heater warns of improper operation and risks a destructive puffback.

See OIL BURNER SOOT & PUFFBACKS

On 2018-10-21 16:14:47.099480 by (mod) -

TJ

Watch out: A gas fired heating appliance of any kind that is sooting is extremely dangerous, likely to produce fatal carbon monoxide gas that can kill people in the building.

The right action for you to take is turn OFF the heater right away, turn off the gas supply to it, and call for repair from a trained gas appliance service technician.

The actual problem cause could be a combustion air deficiency, a venting defect, a burner defect, but it's not likely to be a thermocouple, nor the wires, that you replaced.

On 2018-10-21 16:02:44.785054 by Anonymous

@Tj,
Help me before I just let this piece of love house explode already!!!

On 2018-10-21 16:01:11.469582 by Tj

Water heater started sooting, been months. So bought brand new regulator and manometered it to 11.5 bought a brand new gas control valve for water heater and bought brand new wires thermo couple or thermo pile, metal pipe going to chimeney isn't blocked either. So as of now I took my thermo switch off and attached the splicer and I run to hot then shut off for a couple days then warm it back up then shut it off again. New thermo switch is on back order...

On 2018-02-01 01:50:40.413967 by (mod) -

I can't assess all of the possible risks of an improperly-operating oil fired heater from just your brief text, Lori but generally if you can remove the soot by cleaning then I doubt there would be a measurable soot hazard remaining.

On 2018-01-28 17:46:52.707010 by Lori Riss

We rent and we had black soot coming out of chimney they fixed the unit but so many items had a light coating of soot is this safe as long as we clean it.

On 2017-12-01 17:25:00.534496 by (mod) -

OK

Let me kniw what you are told, and we may be able to offer further suggestions.

On 2017-12-01 17:22:32.695950 by MW

Thank you for your prompt reply.i contacted the service engineer and he told me that he would call tomorrow.

On 2017-11-30 23:21:09.100487 by (mod) -

That sounds like the oil burner needs service, although I can't be sure exactly what the cause of poor combustion is - examples are dirty nozzle, improper adjustment, inadequate combustion air, a bad Transformer, even a loose electrical connection.

On 2017-11-30 19:16:14.233773 by M. Wade

I have a myson velaire vitesse oil boiler .it is quite old but has been serviced annually. Serviced in June. The problem is that it is kicking out slightly darker smoke from the chimney and there is a smell to it.i checked inside the flue and it was sooty and oily at the same time.any advice would be most appreciated

On 2017-11-13 01:12:58.613926 by (mod) -

I don't know, anon, as I have no information about the condition of your heating system.

However black soot in any quantity collecting on or around an oil-fired heating Appliance usually means that it's not working correctly and needs service bash at a minimum cleaning and adjustment.

The danger is that as the burner runs increasingly poorly you could have a puff back explosion that blows sucked all over the place.

However if the quantity of soot is really minimal, just a few flecks, it may be a fairly normal operation since oil-fired heating equipment never runs perfectly clean and always produces some soot that increases over the course of the heating season.

On 2017-11-12 14:44:15.329836 by Anonymous

why is there black soot on the flue of my oil boiler?

On 2017-02-19 17:33:26.599374 by (mod) -

Nick

After cleaning a sooted oil fired boiler it's normal for a bit of loose soot and debris to blow out of the flue at the next one or two firings. If it continues past that I think more repair is order.

But for SAFETY you need more expert work on your boiler to find out why it was so sooted-up and to make sure that the burner is operating properly. An incomplete list of examples of problems could be a bad transformer, bad electrodes, clogged nozzle, leak in oil line, inadequate combustion air, dirty blower fan.

Just cleaning the boiler won't fix those issues.

Fire on boat - really bad.

On 2017-02-19 16:10:17.694467 by Nick

I work on a boat and on hear we have a Sabre boiler with a Beckett Series oil burner, my question is I got on the boat a few days ago and was told that their was a lot of black smoke coming from stack for boiler, so I shut it down a started to inspect it, found that there was a hole lot of soot and rust build up in the side panel,

cleaned best I could, and in the stack ( from where smoke comes out the back top of boiler and the goes up and out of stack). I cleaned this out, cleaned fire box out took like 4 to 5 hours to clean all, I'm guess this had not been done in some time.

Now the next day I have little black specks coming out of stack, like when you fire up a torch and you are setting it just a black little floties,

I have adjusted the air intake on it and am wondering if I just need to add a little more air or if this is normal because of the cleaning that I done. Any help would be great. Thanks

On 2017-02-09 17:18:24.936926 by (mod) -

Pauline,

I would like to help you, but I am afraid that I cannot offer specific advice because I have so little information about your heating system, what is installed or exactly what is the operating problem.

For example a flame problem with an oil burner could be due to a number of problems such as inadequate combustion air or simply a dirty oil burner nozzle.

Please keep in mind that there are life safety issues involved here. That means that you need a qualified, trained oil heat service technician to inspect clean and adjust your oil burner. It's not something that a homeowner can do by themselves.

For one thing you don't have the training to recognize the problem, and for another you won't have the proper testing equipment Northern repair parts.

On 2017-02-09 14:31:14.397167 by Pauline Clark

We have an oil burner which spots up constantly and the fire is causing problems with eyes stinging and watering. We can't seem to find any experts to inspect the fire.

Can you give us any advice please?

On 2016-12-20 23:20:27.190213 by (mod) -

Maria:

If your heater is now working properly and venting through a safe chimney properly, then you won't find CO in the home.

I don't think an "air test" is a reliable approach to screen for a prior one-off event: more likely the soot particles have settled down onto building surfaces.

Only if the heating system is continuing to work unsafely and producing soot would you be likely to find high airborne soot now.

But blowing soot around a home is indeed an obnoxious respiratory irritant.

Try going to some flat surfaces and wiping with a dry paper towel. If you see black soot that tells us that you need to have some extensive cleaning done, perhaps using a HEPA-rated vacuum cleaner.

The health questions are ones to take to your doctor. The hazard depends on the level and duration of exposure to anything as well as the individual's health and vulnerability.

DO NOT sleep in this home before you have working, properly-located smoke detectors and carbon monoxide detectors.

On 2016-12-20 07:36:45.864732 by maria

i have a gas wall heater which was discovered to be pushing very high carbon monoxide levels into my home. it was shut off by the gas utility (pg&e)

and a service technician said the flue was full of soot. they scraped it clean and ran the heater for an hour, after which i shut it off and havent restarted it because that day i started sneezing and coughing, and my eyes, throat, and lungs all have been burning ever since.

CO levels aside, how do i go about checking whether the air in my home is now making me sick? do i see a doctor about carbon dust inhalation?

On 2016-02-14 16:46:01.683252 by (mod) - When a burner keeps sooting up look for these problems

Mark:

When a burner keeps sooting up I"d look for any of several problems:

- a draft problem

- a combustion air problem

- a dirty squirrel cage blower fan that is not giving enough combustion air or wrong settings on the air shutter on the burner

- wrong nozzle

- leaks at the oil line or nozzle adapter

- wrong electrode settings

- oil pressure below 100 psi at the fuel unit

On 2016-02-14 15:33:04.183382 by Mark

oil camray boiler keeps sooting up. I've changed the oil pump and nozzle and cleaned it right out (hoovered an all) but after a few hours it's back to the same. It has a vertical flue which is 10 years old the same as the boiler. The oil pressure is good but my analyser is reading 14. Something percent. I've tried to lower it but it won't go any lower.

On 2016-01-09 15:10:13.117456 by (mod) -

If you mean that a gas burner is not burning properly SHUT OFF THE APPLIANCE IMMEDIATELY including the gas supply as you are risking a fire or explosion.

I can't diagnose a gas burner from a 7 word e-text, sorry. You may have a gas leak, an improperly adjusted burner, or some other unsafe condition.

On 2016-01-09 12:37:34.469417 by Anonymous

What causes aga burner to catch fire

On 2015-12-26 18:21:43.818814 by (mod) -

Susan

Your oil heating system is not working properly and needs very prompt service (maybe just cleaning and adjustment, or maybe repair);

the risk as the burner gets sootier and sootier is a PUFFBACK EXPLOSION (search inspectapedia for that term for more details)

On 2015-12-26 17:42:47.960492 by susan

why does my oil furnance blow smoke in the house and specks of oil every where

Question: damper not working right

(Oct 22, 2011) Roger said:

I have a barometric damper that I'm sure doesn't function properly, due to the fact that it doesn't open lose during heating, but on start up, I am getting blow out out a fine soot through the damper.

Even if it was opening and closing, I still would get the "blow back" if that's what is meant by the term.

There is not a signifcant amount of soot build up (I just cleaned everything, but it wasn't that bad to begin with.

Why am I getting the soot blowing out of the damper. Also, the flame is yellow. Good or bad?

Reply:

Roger

A bang and blow out of soot at oil burner startup might be a clue that the burner shutdown cycle is dribbling oil into the combustion chamber, where it is ignited at next start.

The risk is a messier and more dangerous puffback. I'd ask my heating service tech to take a look.

Question: call your local heating service company for boiler cleaning and maintenance or a chimney sweep for chimney cleaning

(Nov 23, 2012) dee said:

yes in michigan i have base board heat and in side the furnace it looks like a snake like coils out of cast iron but anyway

i tryed to clean it out with a long wire brush i was getting out a lot of black soot i had to throw away too vac that i tryed to clean it up with is there a place that will clean that out for me thank you for your time.

Can you please tell me if you know a company in or around warren Michigan I can call to have it clean out thank you for your time

Reply:

Dee

Heating service companies do this cleaning.

Question:

(Jan 24, 2013) Karen A Driscoll said:

We have a propane hot water heater of 9 years old. Manufacturer will not stand behind the warranty. It has been out of commission for over a month now as we investigate the best way to replace. It has a lot of soot and never been cleaned. Our propane supplier does not know how to clean, suggested a chimney sweep. Now it is suggested to replace with an electric water heater. Any advise?

(May 31, 2014) Donna Lucier said:

We just got a new furnace from Sears.Since then,I've seen charcoal globs of dust coming out of the vents. We have a 61 yr. old home and never had any duct-cleaning ever! What do you think the soot is and why is it coming out of the vents.

Also, our furnace blower is loud. We also have a new Sears humidifier and can feel very much moisture coming from the vents when the humidifier is running.

Reply: soot problem is not acceptable,

Donna certainly this soot problem is not acceptable, and it could also indicate an unsafe heating system installation.
You don't say if your furnace is fueled by oil or gas or electricity.

WATCH OUT: for gas fired equipment, production of soot often means that the system is dangerous and should be shut off immediately as it may be sooting in combination with production of potentially fatal carbon monoxide.

For any fossil fuel fired system soot production means that the system is not set up, adjusted, or installed properly.

The problem could be simply an adjustment, or there could be a more challenging problem to solve with a chimney or with combustion air.

If you have moisture coming out of air vents the humidifier is not working properly and needs to be adjusted or removed.

The risks include leaks into the structure (mold, damage, rot, insect attack), and leaks into the heating system (causing damage to the equipment).

(June 1, 2014) Donna Lucier said:

Thank you so much,Dan,for getting back to me on this! It IS GAS fueled! I will show this to my husband and get it taken care of. I was concerned about this and even though it was inspected, the installation seemed like a rush job to me.

Everything about it seems wrong with the moisture coming out of the vents.

I didn't feel that with our last humidifier and my big concern with that is exactly what you said about mold, dust (and dust mites), rot and insect attacks like silverfish. What about the fact that the duct-work has never been cleaned in 61 years?

I see dust bunnies blowing out onto the floor.Is that a health hazard? God bless you,Sir! You may have saved us both!

Reply:

Donna

Soot production on gas fired equipment is indeed dangerous.

Of course I can't see your system. There could be some other source of dirt blowing through the system.

Be sure you have working carbon monoxide detectors installed properly.

I would turn the system off, contact the company and ask for help from a trained, experienced service rep, noting that the combination of soot and moisture both point to an unsafe installation.

(June 1, 2014) Donna Lucier said:

Daniel, I will do exactly that immediately. Thank you so much for your time and help!

Question:

(Apr 7, 2014) Jim Caggiano said:

What would cause soot on the top 5" of the outside vent from my gas propane furnace. Thanks, Jin

Reply:

I'm afraid that you describe an extremely dangerous condition: improper burner operation - e.g. inadequate combustion air, wrong jets, improper adjustment - that in turn also produces potentially fatal carbon monoxide.

Watch out: a cause could be dangerous flue blockage or poor draft and sooting - risking fatal carbon monoxide poisoning.

Question: oil furnace/hot water system started blowing black smoke and smelled of oil

(June 26, 2014) Anonymous said:

Sorry if this is too specific, but we just moved to an old farmhouse and today the vent (outside) that is connected to the oil furnace/hot water system started blowing black smoke and smelled of oil I called the fire department.

When they got here it was all gone except for a small reading of carbon monoxide in the basement (nothing to worry about they said) and the soot that covered all the plants next to the vent.

They said it might have been a backfire (?) but that that shouldn't happen in the summer.

Any ideas on what that could mean? The heating company can't get out here until maybe Saturday. I'm worried we're going to need a whole new system =0\

Reply: when is CO normal?

Anon,

First,

Once a heating system is up to operating temperature and draft, carbon monoxide spillage at the equipment ought not be found at all,

Second that may be a sign of inadequate combustion air or poor burner operation,

Finally, a puffback can occur any time that the equipment is running. The summertime comment is mistaken.

Leave the equipment turned off pending service and repair.

Question: what should we do to maintain our Weil McLain D65 boiler?

(Oct 5, 2014) j.lalonde said:

We have a weil mclien boiler in our house.

We have had it cleaned once + have been here since 1965. It is aSeriesD 65-102 water94.5 model#D8 working water pressure 30 Out put 128000 Input 157000. Could you tell me anything about this boiler we should be doing Etc.

Reply:

J.

Cleaning an oil fired heating appliance only once in 50 years is incredible.

That is, I'd be surprised that the system is running at all much less efficiently and safely.

It's true that older slow-speed (1725 RPM) burners and boilers were pretty tolerant of non-maintenance, but it's way past time for an inspection, cleaning, and tuning of the boiler, a chimney safety inspection, an inspection of other safety controls on the system.

I would not assume that the boiler needs replacement just based on age, but if an inspection finds cracking or other costly damage it'd be appropriate to consider a replacement.

If the unit is gas fired that is even more reason for an inspection since an out-of-adjustment gas boiler can more easily produce dangerous Carbonn monoxide gas.

Question: tech said I have too much soot in my vent

(Nov 11, 2014) kelly said:

i just had a oil heater technician at my house. He sad I had to much soot in my vent. Would not service heater. How come? Do I need a new furance?

Reply:

I'm a little surprised as cleaning the system is the tec's job. Perhaps he means that your chimney is blocked and thus unsafe- needing a chimney sweep, cleaning, and inspection.

I infer that your heating system is unsafe.

Give the service manager a call promptly and ask for clarification.

If I were the tech and thought your system were unsafe i would shut it down, red tag it, and explain both the danger and the needed action to you.

Question: does low oil burner-fired boiler temperature mean soot formation in the boiler or water heater?

(Dec 2, 2014) Wayne Fletcher said:

I run my water heater at very low temps. I am so. Fla and don't need my water heated very much.

I am having a lot of soot build up in the chimney which I wash out to cure the problem. Is the soot because I run the burner at such a low temp?

Reply:

Wayne

Watch out: if your water heater is gas fired soot is an indicator of a very dangerous condition - probably also producing potentially fatal carbon monoxide gas.

If the heater is oil fired then it needs service. In all cases also check for adequate combustion air and check the condition of the chimney for safety.

Question: what to do about creosote in a gas-fired boiler

(Dec 20, 2014) brandon said:
I have a gas boiler from the 1960s and creosote has coated the whole inside. The unit doesn't have a good way of coming apart most of the pieces are welded together which has caused difficulty cleaning inside. Any suggestion on a good way to clean? Winter without heat sucks.

Reply:

Brandon this is a job for an experienced heating service tech. Creosote can be quite hard on a surface and thus hard to remove. Heating up, wire brushing, scraping are usually applied. I'm reluctant to advise about other more aggressive measures for a system we know nothing about. But your service tech may, on seeing the system, have a suggestion.

Watch out: creosote formation in a gas boiler is very unsual and suggests that the boiler is sooting. Soot formation on gas fired equipment means the system is dangerous - unsafe- and could kill the building occupants by producing carbon monoxide.

Turn off the system until it has been repaired by a professional.

Question: who will clean my heating flue

Mar 29, 2015) joe bell said:
who can I call to clean my flue pipe from oil heater an up thru roof to get all the soot buildup out

Reply:

Joe:

look in your local phone directory for a chimney sweep - preferably certified by the national chimney sweeps guild.

Question: chemical solvent for removing soot in a boiler?

(Sept 4, 2015) David said:
Is there a chemical solvent that will soften soot buildup on boiler sections?

Reply:

The techs I learned with use mechanical cleaning or on occasion (dangerously so) a high temperature soot removing burn in the equipment.

Question: cost to clean my gas furnace

(Oct 4, 2015) patrick said:
app. how much will it cost me to get my gas furnace cleaned

Reply:

The cost depends on where you live and on the condition of the equipment. A typical annual maintenance call to just inspect and clean the equipment is typically under $500. often about $150 or a bit more, and zero if you have already paid for a service contract.

Question: how do I know if the boiler is leaking water

(Oct 5, 2015) Anonymous said:
How can I tell if the boiler is leaking water

Reply:

YOu may see water on the floor or small leaks that evaporate will leave a light coloured mineral crust of salts around the area of leakage. Look also in the combustion chamber; A thorough inspection would require removing all covers.

Details are at BOILER LEAKS CORROSION STAINS

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• OIL BURNER INSPECTION & REPAIR
• OIL BURNER ELECTRODES
• OIL BURNER SOOT & PUFFBACKS

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