1. Oil Heat North Seattle Community College HVAC Program
Instructor – Mark T. Weber, M.Ed., CMHE
Oil - 1

2. Objectives After studying this chapter, you should be able to:
Describe various types of fuel oil
List and describe the characteristics associated with fuel oil
Describe different methods for storing fuel oil
Explain how oil tanks are sized 2 2

3. Objectives (cont’d.)‏
Explain the importance of periodic oil tank inspection
Describe how fuel oil and air are prepared and mixed in the oil burner unit for combustion
List products of combustion of the fuel oil
List the components of gun-type oil burners
Describe basic service procedures for oil burner components 3 3

4. Objectives (cont’d.)‏
Sketch wiring diagrams of the oil burner primary control system and the fan circuit
State tests used to determine oil burner efficiency
Explain corrective actions that may be taken to improve burner efficiency, as indicated from the results of each test
Describe preventive maintenance procedurs 4 4

5. Safety Checklist
Do not reset any primary control too many times because unburned oil may accumulate after each reset
Do not start a burner if heat exchanger is cracked or otherwise defective 5 5

6. Safety Checklist (cont'd.)‏
Do not start burner with the fuel pump bypass plug in place unless the oil delivery system is configured as a two- pipe system with both a supply and return line
When conducting flue-gas efficiency tests, avoid burns by not touching the hot flue-gas pipe 6 6

7. Safety Checklist (cont'd.)‏
Keep your distance from the ignition arc
Observe all electrical safety precautions
Inspect oil burners and lines for leaks
When installing oil tanks, make certain that all codes are followed
Oil tanks need to be inspected periodically to minimize tank leakage 7 7

8. Introduction to Oil-Fired Forced-Warm-Air Furnaces
Oil-fired forced-warm-air furnaces have two main systems:
A heat-producing system, consisting of the oil burner, fuel supply components, combustion chamber, and heat exchanger
A heat-distributing system, consisting of the blower, and other related components
When thermostat calls for heat, ignition system is powered and oil burner motor starts

9. Physical Characteristics
Lowboy
Often used if there is not much headroom
May have a cooling coil on top to provide air conditioning
Upflow
Vertical furnace in which the air is taken in at the bottom, forced across the heat exchanger and out the top

10. Physical Characteristics (cont'd.)‏
Downflow
Looks similar to an upflow furnace except that air is drawn in from the top and forced out the bottom
Horizontal
Usually installed in a crawlspace under a house or in an attic
Available with right-to-left or left-to-right airflow

11. Fuel Oil
Delivered to the customer in liquid form and stored in tanks either aboveground or underground
Oil used in residential and most commercial systems in the United States: basically diesel fuel that has been dyed red for tax purposes
Derived from crude oil by a process of distillation called cracking

12. Fuel Oil (cont'd.)‏
There are six grades of fuel oil and a numbering system, 1 through 6, is used to identify each grade
The lower-numbered oils are called light oils because they weigh less per gallon than the higher-numbered oils
The lightest of these, No. 1, is most commonly known as kerosene
Fuel oil No. 2 is known as pentane and is the most commonly used

13. Fuel Oil (cont'd.)‏
The ASTM sets standards for acceptable ranges for fuel oil characteristics:
Flash point
Has to do with the maximum safe storage and handling temperature for the fuel
Lowest temperature at which vapors in air above the fuel ignite briefly when exposed to a flame
Ignition point
A few degrees higher than flash point
Flame keeps burning because vapors keep rising from liquid

14. Fuel Oil (cont'd.)‏ Viscosity Carbon residue
Thickness of the oil under normal temperatures
Heavier oils are thicker at the same temperatures
Expressed in Saybolt Seconds Universal (SSU)‏
Carbon residue
Amount of carbon left in a sample of oil after boiling in an oxygen-free atmosphere
Properly burned oil has no appreciable residue

15. Fuel Oil (cont'd.)‏ Water and sediment content Pour point
Attempt to ensure that water, sediment, and other contaminant levels are as low as possible
Sediment can form when rust forms on internal pipe; tank surfaces and sludge can form when water condensation reacts with the fuel oil
Pour point
Lowest temperature at which the fuel can be stored and handled
No. 2 oil is one of the lower pour point fuels; can be used down to 20°F

16. Fuel Oil (cont'd.)‏ Ash content Distillation quality
Amount of noncombustible materials contained in the fuel oil
Can be abrasive and wear down burner components
Distillation quality
Describes ability of the oil to be vaporized
Lighter oil turns into vapor easier than heavier oil

17. Oil Storage
When possible, install tanks above ground for environmental reasons
Follow all local codes when installing
Oil tank sizing
Tanks are available in sizes from about 100 gallons to over 1000 gallons
Two main issues in selecting tank size are frequency of oil deliveries and quality of oil with respect to storage time
Tank should hold about 1/3 of the annual oil consumption

18. Oil Storage (cont'd.)‏ Underground tanks
Tanks installed underground must be protected against corrosion
The most popular types are the STI-P3 tanks and fiberglass tanks
See Figure 32-7 in text

19. Oil Storage (cont'd.)‏ Aboveground tanks Indoor oil storage
Typically fabricated from 12 gauge steel and hold between 275 and 330 gallons of oil
Polyethylene/steel tanks: tank within tank
Galvanized steel outer tank protects the polyethylene inner tank and provides secondary containment in the event of a leaking inner tank
Indoor oil storage
Reduces temperature fluctuation as well as moisture and condensation inside the tank

20. Oil Storage (cont'd.)‏ Oil tank inspection and maintenance
Aboveground tanks should be painted periodically and inspected on a regular basis
STI-P3 tanks should be checked to ensure protective anodes are in good working order
Tank piping should be inspected regularly for imperfections and leaks; always check for loose or missing vent and fill caps

21. Oil Storage (cont'd.)‏
Tanks should be checked for water at least once a year
If water is present, the source of water should be identified and the situation corrected
Tanks are tested for water content by placing a water-sensing paste on the oil tank stick
Visually inspect aboveground tanks for damage to pipes, caps, oil lines, tank legs, and gauges and check for traces of oil under the tank

22. Fuel Oil Supply Systems
Two common piping configurations:
One-pipe system: only one pipe runs between the oil storage tank and the oil burner
As oil is needed, it flows from tank to burner

23. Fuel Oil Supply Systems (cont’d.)
Two-pipe system: one pipe is the supply and the other acts as the return
Oil flows at maximum capacity to the burner where the system uses what it needs and the rest flows back to the tank via the return line
One-pipe system is used when tank is located above the oil burner; two-pipe when tank is below

24. Fuel Oil Supply Systems (cont'd.)‏
Key points about fuel oil lines and piping:
Oil lines should be sized at a minimum of 3/8” OD copper lines
Oil lines can be constructed of wrought iron, steel, or brass pipe connected with malleable fittings; never use cast-iron fittings
Never use PVC pipe for oil lines
Use only flare connections to join oil lines

25. Fuel Oil Supply Systems (cont'd.)‏
When needed, use only a non-hardening, oil-resistant pipe joint compound
When installing oil lines, make the runs as short as possible, use as few fittings as possible, and avoid kinking the lines
Be sure that all oil lines are secured and protected from damage
Ensure lines run outside are well insulated

26. Fuel Oil Supply Systems (cont'd.)‏
Underground oil lines should be installed with secondary containment
There should be a shutoff valve on the suction line at the oil burner
Fill and vent pipes should pitch toward tank opening to prevent formation of oil traps
A vent alarm should be installed in all tanks at the vent opening

27. Fuel Oil Supply Systems (cont'd.)‏
The oil dearator allows a one-pipe system to function as a two-pipe system
Auxiliary fuel systems get the fuel supply to the burner if it is too far above the tank
Fuel line filters remove fine solid impurities
Oil safety valve (OSV) stops oil flow if there is a leak in the suction line

28. Preparation of Fuel Oil for Combustion
Liquid oil must be atomized (broken up into droplets)‏
Oil droplets mix with air, which contains oxygen
High-pressure gun-type oil burners feed oil through a nozzle under pressure and force air through a tube surrounding it

29. By-Products of Combustion
The correct ratio of fuel to air is required for proper combustion
1 lb of fuel oil must be mixed with about 3 lb of oxygen for complete combustion to occur
Air is approximately 79% nitrogen and 21% oxygen; 192 ft³ are needed to burn a single pound of fuel oil
Most oil burners provide 50% excess air
Needs 21.6 lb or 288 ft³ of air for 1lb fuel oil
By-products are heat, flue gases, CO2, and water vapor

30. Gun-Type Oil Burner
Oil and air are forced into the burner for mixing and ignition
Flame retention burner design improves on conventional design
Main parts:
Burner motor provides power for fan/pump
Burner blower forces air into the chamber
Fuel oil pumps deliver oil to the chamber
Nozzle atomizes air prior to ignition

31. Gun-Type Oil Burner (cont'd.)‏
Air tube delivers air to the chamber
Electrodes vaporize atomized oil droplets and provide spark for ignition
Ignition transformer provides high voltage to electrodes
Solid state igniters are found in newer oil burners, replacing ignition transformers
Primary control unit provides means for operating the burner and a safety function to shut down the burner if icombustion does not occur

32. Gun-Type Oil Burner (cont'd.)‏
Figure Diagram that compares the flames created by conventional and flame-retention oil burners 32

33. Oil Furnace Wiring Diagrams
Includes wiring for the fan, the oil burner primary, and the 24-volt control circuits
The limit switch is a safety that passes power to the primary control
On a call for heat, power is passed to the ignition transformer, burner motor, and fuel valve
The safety device will shut the burner down in case of a problem

34. Safety Controls Stack switch safety control Cad cell safety control
Positioned in the flue pipe
Bimetal heated by combustion flue gases
Hot contacts allow the burner motor to continue operation
Cold contacts allow current to flow through safety switch heater
Cad cell safety control
When the burner fires, the cad cell senses light and its resistance drops, causing the triac to open

35. Combustion Chamber
Atomized oil is burned in suspension in the combustion chamber
Oil that is not completely ignited will hit the chamber walls and condense
Oil vapor hitting chamber walls and condensing will lower combustion efficiency
The burner must be matched to the chamber
The chamber is a box to contain the fire

36. Heat Exchanger
Transfers heat from combustion to the air that is circulated to heat the structure
Separates flue gases from the air circulated to heat the structure
Should be inspected for cracks during normal service
Most state codes prohibit repairing cracks by welding
Correct airflow across the heat exchanger is important

37. Condensing Oil Furnace
More efficient than conventional furnaces
Combustion system includes:
Burner and related components, combustion chamber, as many as three heat exchangers, and vent fan and pipe
In third heat exchanger, temperatures are reduced below dew point
Heated air circulation system includes:
Blower fan, housing, motor, plenum, and duct system

38. Service Procedures Pumps: connect vacuum and pressure gauges to pump
Pressure should be 0 psig if tank is above burner
If tank is below burner, pressure should not be lower than 17 in. Hg
1 in. Hg for each foot of vertical lift
1 in. Hg for every 10 feet of horizontal run
Nozzle pressure should be steady at 100 psig or 140 psig depending on the burner assembly

39. Service Procedures (cont'd.)‏
Burner motors: press reset button to see if motor will start
Check for voltage between orange and white wires of the primary control
If there is no voltage, the primary control needs to be checked
Check for voltage between black and white wires on the burner motor
If there is voltage and the motor does not turn, the motor is defective

40. Service Procedures (cont'd.)‏
Nozzles: do not try to repair a nozzle
Nozzles are often replaced annually
Always make certain to use the correct nozzle size
Use proper tools to remove nozzles
Overheating nozzles can result in oil breakdown
After-drip can result in the nozzle getting clogged

41. Service Procedures (cont'd.)‏
Ignition system
Transformer
Turn power off and swing the transformer back
Shut off fuel supply to the burner
Restore power to the burner
Check for output voltage of 10,000 volts
Electrodes
Ensure the spark gap settings for proper position
Check insulation for cracks
Keep electrodes clean

42. Combustion Efficiency
Areas to test for proper combustion:
Draft: determines rate at which flue gases pass through the furnace
Too much increases stack temperature, too little can result in pressure and smoke
Smoke: indicates incomplete combustion and fuel waste
Net stack temperature
CO2: good indicator of combustion efficiency
Low reading indicates fuel oil has not burned completely

43. Summary
Oil-fired furnaces are made up of heat- producing and heat-distributing systems
No. 2 fuel oil produces about 140,000 Btu/gal
Fuel oil must be atomized before combustion 43 43

44. Summary (cont’d.)‏
Typical oil burner contains a motor, blower, fuel pump, nozzle, electrodes and primary control
Nozzles rated by flow rate, angle, and spray pattern
Ignition transformers and electronic igniters provide the high voltage needed for spark ignition 44 44

45. Summary (cont’d.)‏
The primary control controls burner operation and safety functions of the system
Primary controls can use cad cells or stack relays
The resistance of a cad cell decreases as the amount of light sensed increases 45 45

46. Summary (cont’d.)‏ The stack relay responds to the stack temperature
Condensing furnaces are more efficient than conventional furnaces 46 46

47. For more information please contact Mark T. Weber, M.Ed, CMHE At
North Seattle Community College