HVAC Excellence Oil Heat Certification flashcards
HVAC Excellence Oil Heat · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Heat content of No. 2 oil
- No. 2 heating oil releases roughly 138,000 to 140,000 Btu per gallon when burned, the figure used to compute input rate from nozzle size and pump pressure.
- Nozzle flow vs pressure
- Flow changes with the square root of pressure: new gph equals rated gph times the square root of new psi divided by rated psi. Doubling pressure raises flow about 41 percent.
- Hollow-cone nozzle use
- Hollow-cone nozzles produce a ring-shaped pattern used in most residential retention-head burners; they atomize well at 100 psi and match the burner's air pattern.
- Solid-cone nozzle use
- Solid-cone nozzles deliver a filled spray pattern, often used in low-input or certain commercial burners where a fuller pattern improves mixing with combustion air.
- Electrode tip gap
- Electrode tips are typically set 1/8 to 5/32 inch apart; too wide a gap weakens the spark, too narrow promotes carbon bridging and hard starts.
- Electrode position above nozzle
- On retention-head burners the electrodes usually sit about 1/8 to 5/32 inch above the nozzle centerline and 5/32 to 3/16 inch ahead of the nozzle face.
- Cad cell dark resistance
- A clean cad cell in darkness reads well above 20,000 ohms, often 50,000 or more; low dark resistance suggests a shorted or contaminated cell.
- Cad cell flame resistance
- When viewing flame, cad cell resistance drops below about 1,600 ohms; the primary control uses this threshold to prove flame and prevent lockout.
- Trial for ignition
- The timed period after the burner starts when the primary control looks for flame proof; if the cad cell stays dark beyond this period, the control locks out.
- Primary control lockout
- On flame failure the primary control shuts off the burner and locks out, requiring manual reset; repeated lockouts indicate nozzle, electrode, or cad cell problems.
- Overfire draft target
- Most oil-fired appliances are set to about minus 0.02 to minus 0.04 inches water column overfire draft, measured through the inspection port at steady state.
- Breech draft target
- Breech draft is typically minus 0.02 to minus 0.06 inches water column; the barometric damper is adjusted to hold this range as the burner cycles.
- Barometric damper function
- A barometric damper opens to admit room air into the flue, stabilizing draft so changing chimney conditions do not alter combustion air or efficiency.
- Smoke test meaning
- A smoke test measures unburned carbon in flue gas on a 0 to 9 scale; a trace (No. 1) or zero indicates clean combustion, while higher numbers mean soot and wasted fuel.
- Target CO2 range
- A well-tuned oil burner typically produces about 11.5 to 12.5 percent CO2 in the flue gas, corresponding to moderate excess air and good efficiency.
- Excess air effect
- Excess air above roughly 50 percent lowers flue-gas temperature but raises stack loss, reducing steady-state efficiency; air is set by the burner's air shutter or band.
- Steady-state efficiency
- Calculated from flue temperature, room temperature, and CO2 or O2, a clean residential oil burner usually reaches about 85 to 87 percent steady-state efficiency.
- Stoichiometric air for oil
- Complete combustion of No. 2 oil needs about 14.4 pounds of air per pound of fuel, roughly 1,920 cubic feet of air per gallon of oil.
- Two-line fuel system
- A two-pipe system returns unused oil to the tank, allowing lifts beyond about 8 feet and preventing air lock; the bypass plug must be removed from the pump.
- Single-line fuel system
- Used when the tank is above or near the burner with limited lift; oil is drawn from the tank and any excess returns through the pump's internal relief.
- Oil filter placement
- A listed filter is installed in the suction line between tank and pump, protecting the nozzle and pump from grit; clogged filters cause delayed ignition and lockout.
- Fusible oil valve
- A heat-actuated valve on the tank outlet closes when exposed to fire, stopping gravity flow of oil to the burner area during a fire.
- Tank gauge purpose
- A gauge or sight device indicates oil level so the tank can be filled safely and the burner not run dry; running dry introduces air and causes lockout.
- Nozzle sizing basis
- Nozzle gph is chosen from the appliance input rate divided by oil Btu content, then adjusted for actual pump pressure using the square-root flow rule.
- Delayed ignition causes
- Delayed ignition, a puff or rumble at startup, usually comes from worn electrodes, wrong gaps, a dirty nozzle, low pump pressure, or insufficient draft.
- Puffback definition
- A puffback is a small explosion of unburned oil vapor in the combustion chamber, often from delayed ignition or a flooded chamber; it coats surfaces with soot.
- Combustion air requirements
- Oil burners need adequate combustion air from outdoors or a large indoor volume; a confined boiler room requires dedicated openings sized to the appliance input.
- Flue gas temperature
- Stack temperature on a clean residential oil appliance is typically 350 to 500 degrees Fahrenheit; rising stack temperature signals soot or heat exchanger fouling.
- CO in flue gas
- Carbon monoxide above about 100 ppm in the flue gas of an oil burner suggests incomplete combustion from poor air adjustment, soot, or a blocked flue.
- Heat exchanger cleaning
- Soot on heat exchanger surfaces insulates them, raising stack temperature and lowering efficiency; brushing and vacuuming restore heat transfer.
- Chimney vs power venting
- Natural-draft oil appliances vent into a lined chimney; side-wall power venters are used where a chimney is unavailable and must be interlocked with the burner.
- Fuel unit bypass plug
- The bypass plug in a two-pipe oil pump directs return oil to the tank; leaving it in on a single-pipe system overpressures the pump and can damage the seal.