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Oil Burner Puffbacks: this article explains the cause, cure, and prevention of potentially dangerous and sooty oil fired heating equipment puffbacks that can occur at an oil fired boiler, furnace, or water heater.

Separately, diagnosing black stains on indoor surfaces in the living space, possibly caused by oil fired equipment sooty operation or puffbacks, is discussed at THERMAL TRACKING & HEAT LOSS.

This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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What Causes Sooty Puffbacks at Oil-Fired Heating Boilers, Furnaces, Water Heaters

Leaks in the equipment oil supply piping, often visible as oil drips or leaks that occur when the equipment is not running, become air-leaks into the oil piping and oil burner when the burner is running. Our photo (left) shows heating oil drips on the floor near an oil burner. An alert home owner, home inspector, or heating service technician should recognize the meaning and importance of this clue. To atomize and burn heating oil, the oil burner's fuel unit compresses incoming heating oil to 100 psi or more. Because any extra air in the heating oil piping is also compressed to high pressures (often more than 100 psi) during oil burner operation, any air bubbles present in the system when the oil burner stops its run cycle is exposed to a pressure drop inside the system. The 100 psi air bubble expands, pushing additional un-burned heating oil out of the end of the oil burner nozzle and into the combustion chamber where it may accumulate until, in a dramatic "BANG!" the unburned oil is ignited at the beginning of a future oil burner on-cycle. Oil burner shutdown problems: Incomplete heating oil combustion may also occur if the "shut-down" phase of oil burner operation is not working properly. Inside of the fuel unit of most oil burners is a spring-loaded valve whose job is to quickly and securely stop oil flowing to the oil burner nozzle the moment that the oil burner's fuel unit RPM's begin to slow - when the oil burner is turning "off" at the end of a burn cycle. Even a small amount of dirt on the seat of this oil valve can cause it to leak oil into the combustion chamber instead of making a clean oil-flow shutoff. Poor oil burner maintenance: if an oil burner is running poorly, for example with a dirty oil spray nozzle that has become partly blocked, the result is a poor flame and possibly incomplete combustion of the heating oil being sprayed into the fire chamber. This, too, can lead to accumulation of un-burned heating oil and a subsequent ignition and puffback.

Underlying chimney or heater installation problems: Keep in mind that the root problem may be more than just a need for an oil burner tune-up. For example a too-short chimney can be the cause of inadequate draft that leads to sooty burner operation and poor heating economy. See OIL BURNER NOISE SMOKE ODORS and see Chimney Too Short. Our photo (left) shows soot blowing out around the barometric damper - this system is having trouble and needs service. Watch out: Sooty oil burner operation is a warning: you may be headed for a puffback: Sooty oil burner operation, blowing soot into the boiler room or other building areas, is not normal and it means that the system needs inspection, diagnosis, service, and repair.

Oil Burner Furnace or Boiler Puffback Warning Signs

Guide to Preventing Oil Burner Puffbacks in buildings

BOILER OPERATING PROBLEMS discusses the signs of improper oil fired hot water at operation. Warm air furnaces are discussed at FURNACES, HEATING, and problems with loss of heat are discussed at NO HEAT - BOILER / FURNACE DIAGNOSIS.

Questions & Answers on Oil Fired Heating Equipment Puffbacks

Question: Do "faulty boilers" cause puffbacks? Where do I look for puffback damage to the boiler itself?

Reply: Do faulty boilers cause puffbacks? No, faulty boiler or chimney maintenance is the root cause of puffbacks

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with or cause of malfunction in a heating boiler. That said, here are some things to consider:

Your quotation from your insurance company stating that the puffback was caused by a "defective heating boiler" is confusing because it is not a precisely correct description of heating equipment puffback problems.

The explanation we offer of the mechanism of a puffback in oil fired heating equipment is more detailed than a typical insurance adjuster would offer even if s/he understood the cause of puffbacks, but our explanation is also the correct one.

Our photo (above left) shows soot fragments on top of a water heater that was installed close to an oil-fired heating boiler that was not operating properly - the same boiler whose soot was deposited on the garage ceiling and walls in our earlier photo just above. Failure to notice and do something about this sooty boiler operation is a failure to notice and correct a boiler operation or maintenance problem.

The various possible underlying cause of excess oil that is ignited at the start of a heating boiler "on" cycle and that fuels the puffback, are listed in the article starting with "leaks at equipment oil supply piping" and include a variety of problems.

But nearly all of the problems that are at the root cause of a puffback are maintenance or installation errors or omissions. Failing to detect and fix an oil line leak, failure to detect and correct a dirty oil burner nozzle, failure to observe and correct an oil burner shutdown problem (caused by dirt in the system) are examples.

A bad chimney installation or design is a different puffback cause that is not a direct boiler maintenance issue, but even in that case, a bad chimney (too short for example) that was causing poor boiler operation ought to be diagnosed by the heating service tech and ought to result in a recommendation that it be corrected.

None of these are innate defects in the heating boiler itself. Rather they are defects in installation or maintenance. So I would not use the term "defective boiler" to explain a puffback. I'd use the terms "improper boiler operation" or "inadequate heating equipment maintenance".

I suspect that your insurance company either does not understand these facts, that their policy does not distinguish between improper or inadequate maintenance of the heating system and actual defective heating equipment, or that they are speaking a bit loosely (read carelessly) and are calling improper or inadequate maintenance (your responsibility) a "defective boiler".

My OPINION is that in general and quite often, a homeowners' insurance policy limits coverage where the root cause of a loss is improper or inadequate maintenance - those are exactly what I consider to be at the root of most oil burner puffback problems.

Where do I look for puffback damage to the boiler itself?

Unless a visual inspection of the exterior of your heating boiler (or water heater) shows obvious bulges or cracks or missing parts (for example a blown-off inspection port cover) I don't think a homeowner can safely and accurately assess the condition of the heating system after a puffback.

Your heating service technician would be expected to examine the combustion chamber and the accessible/visible boiler internal surfaces and components for physical damage as well as to accurately diagnose and fix maintenance problems that can cause puffbacks.

And you won't be able to see the "amount of unburned oil" that damaged the boiler or that caused a puffback because that oil is gone - consumed in the burning and explosion of the puffback. Furthermore, because of the physical shock to boiler components during a puffback explosion, I wouldn't assume that the post-puffback boiler would run exactly as it was running before that event. For example a puffback could loosen an oil line connection, resulting in a greater air or oil leak than was present before the event.

The closest we can come to guesstimating the history of a puffback would be to note reports of the history of boiler operation complaints (odors, noises, sooting), the frequency and extensiveness of prior heating equipment maintenance and/or service calls, and the date of the last service call before the puffback.

Finally, although it is much less likely, a boiler that had just been serviced, and serviced properly, could have still have a puffback if, for example, a contaminant in the fuel tank or fuel delivery led to a clogged burner nozzle.

Follow-Up remarks: Inherent Vices in Oil Burners that Contribute to Puffbacks?

An inherent vice in an oil burner or oil fired heater that might contribute to a puffback might be a boiler or boiler control design that made the unit difficult to properly clean and service or adjust, but I'm not aware of such.

Oil burner operation that leads to what I call "sloppy" oil burner shut down or start-up can lead to un-burnt heating oil in the combustion chamber, as we enumerated in the puffback article where I've included this discussion.

About including the oil burner or the whole heater in the insurance claim, I pose that you'd need an onsite expert who could explain and document damage to the equipment that occurred as a result of the puffback, as opposed to simply causing the puffback.

Wear and Tear on Oil Burners Contribute to Puffbacks?

"Wear and tear" contribution to an oil burner puffback sounds theoretically possible but is outside my experience. In my experience it's proper maintenance that is central to proper oil burner operation, combined with two additional factors:

Occupants or owners need to notice when the oil fired heating equipment is not working normally (smells, soot, odors, loss of heat), and then to ask for service and repair.

Service technicians need to notice conditions that are likely to presage or even explain a future puffback such as excessive sooting, chimney draft problems, even more subtle clues to draft problems such as a missing draft regulator, visible oil leaks, difficulty obtaining proper draft at the fire and in the breech, repeated service callbacks.

There is a problem facing the service technician: too often the tech might notice a clue that indicates a problem that needs investigation or repair, but the tech has been given a large number of service calls to make and is thus in too much of a rush to even bring it up with the homeowner, or equally common, the technician mentions the concern and the homeowner says "Stop trying to increase your bill, you are already charging me too much, just clean and tune the boiler.".

Oil Tank or Oil Piping Contribute to Oil Burner Puffbacks?

We discuss oil line leaks (air in or oil out) as a common and important cause of oil burner poor operation that can ultimately lead to a puffback.

A problem with the oil tank itself that might be related to a puffback might be a water leak into the tank that led to water in the fuel, picked up when the oil level was low (water waits on the bottom of the tank) or right after an oil delivery (stirs up water in the tank) and that subsequently led to poor oil burner operation.

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NOISE CONTROL for HEATING SYSTEMS

ODORS FROM HEATING SYSTEMS

OIL BURNERS
OIL BURNER INSPECTION GUIDE
OIL BURNER NOISE SMOKE ODORS
OIL BURNER SOOT & PUFFBACKS
OIL FILTER MISSING
OIL FUEL TYPES & CHARACTERISTICS
OIL ODORS, LEAKY OIL TANK PIPING
OIL PUMP FUEL UNIT
OIL LINE CLOGGING FIX
OIL LINE SAFETY VALVES
OIL SPILL CLEANUP / PREVENTION

SAFETY HAZARDS & INSPECTIONS
SAFETY HAZARDS GUIDE
SAFETY, HEATING INSPECTION
SAFETY,HOME HEATING TIPS
Safety Recalls, Chimneys, Vents, Heaters
  BLUE vs YELLOW COMBUSTION FLAMES
  BLUERAY Recall
  CHIMNEYS & Flues - Asbestos Transite
  Goodman HTPV RECALL
  Heat Recovery Ventilator RECALL
  Lennox Furnace Manuals
  Lennox SAFETY WARNING
  PLASTIC Plexvent / Ultravent RECALL
  Weil McLain RECALL
SAFETY, HEATING INSPECTION
SAFETY,HOME HEATING TIPS
SOOT on OIL FIRED HEATING EQUIPMENT

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
• Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
• Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
• Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
• Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
• National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
• The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
• Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
• Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
• Installation Guide for Residential Hydronic Heating Systems
• ...