Inspection, Tuning & Repair Guide to Heating System Oil Burners
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Oil Burners: Guide to Oil Burners for heating systems, boilers & Furnaces: basic parts, operation, maintenance, performance & money-saving tips
How oil burners work: sequence of operation, oil burner safety controls
How to inspect & repair or replace/upgrade oil burners - homeowner basics, service technician basics, diagnosis, repair
Cleaning & maintenance guide for heating systems
Questions & Answers about oil burners on home heating equipment

Oil burner installation, troubleshooting, diagnosis & repair guide: here we provide a detailed guide to oil burners used on heating systems, boilers & furnaces: basic parts, operation, maintenance, repair, performance and heating cost money-saving tips. This website answers most questions about central heating and water heating systems and provides guides for troubleshooting, inspection, diagnosis, and repairs. Also see our OIL BURNER INSPECTION & REPAIR and additional oil burner inspection, diagnosis, & repair article titles at page left.

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Homeowner's Guide to Oil Burners for Boilers, Furnaces, & Water Heaters

Oil fired heating equipment such as hydronic (hot water) boilers, steam boilers, warm air furnaces, and water heaters, have used heating oil, usually No. 2 heating oil, and various types of oil burners to burn the fuel, thus providing a heat source for nearly 100 years.

This article describes the basics of how oil burners work, and we provide a guide to their inspection and problem diagnosis and repair.

How Oil Burners Work

Refer to the schematic of a conventional oil burner shown below, where we list the major parts parts of a modern oil burner. The sketch at above left is courtesy of Carson Dunlop.

If you need to diagnose and fix a oil fired heating equipment problem with your oil burner, read the text below but also be sure to check out the detailed oil burner articles listed at page left listed under OIL BURNERS, and for more detailed oil burner troubleshooting see OIL BURNER INSPECTION & REPAIR. For heating system troubleshooting that starts before the oil burner, see DIAGNOSE & FIX HEATING PROBLEMS-BOILER or DIAGNOSE & FIX HEATING PROBLEMS-FURNACE

Sequence of steps in home heating or hot water heater oil burner operation:

Electric power on: In response to an aquastat or other heating boiler, furnace, or water heater control, electrical power to the oil burner is switched "on". (ELECTRICAL POWER SWITCH FOR HEAT)

Electricity is connected through a safety control such as the Cad Cell relay labeled "primary controller" in the sketch. Details: Aquastat, Cad Cell Relay, or Stack Relay Switch
Oil burner electric motor starts: The primary controller permits electrical power to flow to the electric motor shown on the right side of the oil burner, causing the motor shaft (not shown) to rotate. See OIL BURNER NOISE SMOKE ODORS.
Oil burner's Electric Motor shaft rotates, driving other parts through a coupling: the spinning shaft of the electric motor extends horizontally through the inside of the oil burner motor where it is coupled first to a rotating squirrel cage fan - the oil burner's air blower (providing combustion air), and second to the the air blower and oil pump (fuel unit).

High speed oil burner motors spin at 3450 RPM. Older "low speed" (and quieter) oil burners use an electric motor rotating at 1725 rpm.
Combustion air: Oil burner blower fan spins, drawing combustion air through adjustable air intake slots on the left side of the oil burner, and simultaneously,
Heating oil delivery: the electric motor shaft extension drives the oil pump (fuel unit) shown on the left-most side of the oil burner in the sketch. The oil pump (oil burner fuel unit such as a Sunstrand™ fuel unit) draws heating oil from the oil tank through a fuel line connected to the oil tank (hopefully through an external oil filter and an internal filter screen) and pressurizes the heating oil to 100 psi or more.

Pressurized heating oil flows out of the oil pump thorough a high pressure oil line into the oil burner tube where it is converted to a fine spray by an oil nozzle attached to the end of the nozzle assembly. Problems with the heating oil fuel unit can lead to loss of heat, noisy operation, and other oil burner operating troubles.

Details about fuel units (heating oil pumps) and their installation, diagnosis, or repair are at OIL BURNER FUEL UNIT. Also see OIL TANKS, OIL TANK PIPING & PIPING DEFECTS
Heating oil ignition: electricity is also delivered to an ignition transformer (the black box on top of the back of the oil burner). The ignition transformer converts the incoming 120V electrical power to very high voltage which is fed to two electrodes attached to the nozzle assembly.

The oil burner nozzle electrodes, separated by a small gap, produce an electrical spark (usually continuous or "continuous ignition oil burner operation" vs. "intermittent ignition" on some older systems) which is right in the path of the oil being sprayed by the oil burner nozzle, causing the oil to ignite.

Safety controls will turn off the oil burner if flame ignition is not successful. This feature prevents continuing pumping un-burned heating oil into the system. See CAD CELL RELAY SWITCH and Stack Relay Switch
Heating oil combustion: the sprayed, burning heating oil heats the interior of the furnace, boiler, or water heater combustion chamber which is normally lined with a material whose surface will get very hot but won't burn.

The combustion chamber liner prevents the oil burner from damaging the cast iron or steel boiler itself, while the hot surface of the combustion chamber liner helps make sure that all of the fine droplets of oil sprayed into the combustion chamber do in fact ignite. Also see COMPLETE COMBUSTION, Stoichiometric for an explanation of complete fuel combustion and boiler or furnace maximum efficiency.
Heat transfer: hot combustion gases from the burning heating oil flow (usually upwards) through the furnace, boiler, or water heater heat exchanger where they transfer heat to that appliance before continuing to flow through a flue vent connector (stack pipe) and then outside through a chimney. See: BOILERS, CHIMNEYS, FURNACES, STEAM HEATING, WATER HEATERS
Electric power and oil burner off: when the aquastat, thermostat, or other primary control senses that the desired temperature has been reached, electric power to the oil burner is turned off, stopping the electric motor from spinning, thus stopping the combustion air blower, oil pump, and turning off the ignition transformer. See AQUASTAT CONTROL Functions and THERMOSTATS

Questions & Answers about oil burners on home heating equipment

Question: We want to install a new oil burner but we don't want to get "robbed"

We have an oil burner that is in the house since 1966. I want to buy a new one that will save us money each month on oil and at the same time be effective, as well as heat up our house. Do you know some names or dealers? I also do not want to get taken or robbed.

We also want to have the sludge taken out of our oil tank, can you recommend someone for both these services. We live on long island and are seniors. - M.P., Rockville Centre, Long Island

Our photo (left) shows an antiquated cast iron Arco™ boiler that was converted from coal to oil. The oil burner on this unit was itself an antique, low-speed unit - though not the system named above nor the upgraded oil burner system described below.

Reply: here are some things to check before upgrading an oil burner

A competent onsite inspection of your entire heating system and chimney, performed by an expert usually finds additional clues that help accurately diagnose a problem or might make clear if upgrading the oil burner on your heating system makes sense. That said, here are some things to consider:

Before even considering a new oil burner, you will want a thorough inspection of your boiler or furnace to be sure it's in good enough condition to be worth the investment. For example if the heater is badly rusted or cracked, it needs to be replaced.

If the heater itself is in good condition, the replacement burner can improve its efficiency and save you money. Our photo (left) shows a modification we [DF] performed to a large cast-iron heating boiler in New York.

The original low-speed oil burner was fired into the very bottom of a quite large, 1930's vintage cast iron boiler that was in good condition but running at the low 70% efficiency range. Originally this had been a coal-fired boiler, converted to burn oil. The original oil burner fired into the bottom of a large combustion chamber.

After inspecting the boiler to confirm that it was not damaged, we installed a new Beckett™ oil burner, firing it up through a higher door on the heating boiler. The system efficiency increased from around 71% (after cleaning and tuning) to 82% efficiency (also after cleaning and tuning) - a heating fuel cost savings improvement of 11 percentage points, but actually a15% reduction in heating oil cost.

We can't make specific contractor referrals for oil burner upgrades nor service. But you can make these efforts to steer clear of a bad experience:

Start by asking for advice from the folks from whom you buy heating oil - you are already their customer. Also ask the oil company to evaluate the level of sludge and water in your heating oil tank and to remove it if that step is required and provided that the tank remains in usable condition. More about oil tank sludge is at OIL TANK SLUDGE.
Check with your local better business bureau for complaints against contractors in your area
Get two or more bids for the oil burner replacement work, and be sure they are bidding on the same type of job and that the scope of work is the same in each bid so you can make a fair comparison
The specific oil burner model needs to be chosen to work well with your heater design
For example, we might like a Beckett high speed oil burner in many applications, but where a specific furnace or boiler has to operate with some risk of backpressure in the combustion chamber we might choose a Carlin™ burner that is designed for that condition.
Don't make final payment for the work until you are happy with the results

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OIL BURNERS
OIL BURNER FUEL UNIT
OIL BURNER INSPECTION & REPAIR
  Diagnostic Sequence
  Visual Inspection at Oil Burner
  Outdoor Clues - Oil Burner Trouble
  Indoor Clues - Oil Burner Trouble
  Trouble at the Oil Tank
  Boiler or Furnace Room Trouble
  Trouble at the Oil Burner - Visual
  Trouble at the Oil Burner - Operation
  FUEL UNIT, HEATING OIL PUMPS
  Oil Burner Smoke Test
  Oil Burner CO₂ Test
  OIL BURNER DELAY VALVE
  Trouble Inside the Oil Burner

Also see these non-technical oil burner articles:
OIL BURNERS, RETENTION HEAD
OIL BURNER NOISE SMOKE ODORS
OIL BURNER NOZZLE & ELECTRODES
OIL BURNER SOOT & PUFFBACKS
OIL BURNER FUEL UNIT pressure settings, pump problems, diagnostics, repairs

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,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
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
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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Inspection, Tuning & Repair Guide to Heating System Oil Burners InspectAPedia® -

Homeowner's Guide to Oil Burners for Boilers, Furnaces, & Water Heaters

How Oil Burners Work

Sequence of steps in home heating or hot water heater oil burner operation:

Questions & Answers about oil burners on home heating equipment

Question: We want to install a new oil burner but we don't want to get "robbed"

Reply: here are some things to check before upgrading an oil burner

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

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

Inspection, Tuning & Repair Guide to Heating System Oil Burners
InspectAPedia^® -