NATE Oil Service key terms

The amount of heat released when one gallon of No. 2 heating oil burns completely, commonly taken as about 140,000 BTU. Technicians use it to estimate input rate from nozzle size and to compare delivered heat with rated output.

Combustion efficiency reflects how completely the fuel burns, read from flue CO2, O2, and smoke. Steady-state efficiency also subtracts stack heat losses, so it is always lower and better represents how much heat actually reaches the building.

The temperature of flue gases measured in the vent connector, used with room air temperature to calculate sensible heat lost up the chimney. High stack temperature with low CO2 usually signals excess air or a dirty heat exchanger.

Stack temperature minus the temperature of the air entering the combustion appliance. It is the driving value for heat-loss calculations, so a hot basement or boiler room raises the baseline and changes the efficiency result.

The efficiency reached after the appliance has warmed up and flue conditions stabilize, calculated from flue gas temperature, CO2 or O2, and ambient temperature. It is the number printed by most electronic combustion analyzers and is not the same as annual fuel utilization efficiency.

A rating that expresses seasonal heat output as a percentage of the fuel energy consumed, accounting for cycling, standby, and off-cycle losses. It is the label value used to compare equipment, while field combustion tests measure only steady-state performance.

The metal passages that separate hot combustion gases from the air or water being heated. Cracks, holes, or heavy soot reduce efficiency, raise stack temperature, and can allow flue gases to enter the supply air stream.

The small negative pressure that pulls combustion air into the burner and carries flue gases up the chimney. It may be natural, from a chimney's height and heat, or mechanical, from an induced-draft fan or power venter.

A hinged damper installed in the flue connector that opens to admit room air and holds a steady negative draft over the fire. Setting it correctly prevents both spillage into the room and excessive dilution that lowers efficiency.

Flue gases escaping from the appliance or vent connector into the building instead of going up the chimney. It is commonly caused by blocked flues, backdrafts, negative pressure, or a draft regulator set too loosely.

The gallons-per-hour rating stamped on an oil nozzle, measured at a standard 100 psi pump pressure. Changing pump pressure changes actual flow, so a 1.00 gph nozzle at 125 psi delivers noticeably more than one gallon per hour.

The cone shape and included angle, such as 70, 80, or 90 degrees, that the nozzle gives the fuel spray. The pattern must match the combustion chamber so oil does not impinge on walls or short-circuit the air pattern.

The refractory-lined or steel cavity where the flame is established and must be shaped to fit the nozzle pattern. A chamber that is too small, wet, or damaged cools the flame, causes smoke, and shortens burner life.

The burner component with slots or vanes that spins combustion air into a tight pattern around the oil spray so the flame stays anchored. Its position relative to the nozzle is a critical adjustment for clean, stable combustion.

The two rods that create the spark that ignites the oil spray. Gap, position, and cleanliness matter, because oil-wet or misaligned electrodes cause delayed ignition, puffback, or no light-off.

A step-up device that supplies high voltage, commonly around 10,000 volts, to the electrodes. Weak output, cracked insulators, or poor grounding can produce intermittent spark and hard starting.

A light-sensitive resistor that detects flame by seeing its brightness and changes resistance accordingly. It is wired to the primary control, which shuts the burner down if no flame is proven within the lockout time.

The burner's main safety and operating control, often called the relay or control board. It starts the burner on a call for heat, monitors the cad cell, and enforces lockout timing and safety shutdown.

The safety state in which the primary control stops the burner after flame has not been proven within the allowed time. Most controls require a manual reset, and a repeated lockout points to a real fuel or ignition fault.

Combustion that occurs well after fuel has begun to enter the chamber, producing a rumble or puffback. Common causes are weak spark, low pump pressure, dirty nozzle, or a nozzle that dribbles after shutdown.

A small explosion of accumulated oil vapor in the combustion chamber that can blow soot and smoke into the building. It usually follows delayed ignition, a flooded chamber, or a blocked flue.

A test that pulls a measured sample of flue gas through filter paper and compares the stain with a scale, usually 0 to 9. A trace, often zero to one, is the target for clean combustion in residential equipment.

Air supplied beyond the amount theoretically needed to burn the fuel, usually expressed as a percentage or read as O2 in the flue. Some excess is required for complete combustion, but too much cools the flame and lowers efficiency.

The burner-mounted pump that draws oil from the tank, pressurizes it for atomization, and delivers it to the nozzle. It also contains a pressure regulator and, on many models, a solenoid valve for cutoff.

The discharge pressure the oil pump maintains at the nozzle, most often 100 psi. Higher pressure makes finer droplets and a wider pattern, while low pressure causes poor atomization, smoke, and delayed ignition.

The small port on the oil pump used to purge trapped air from the suction line during startup. Air left in the line causes erratic pressure, noisy operation, and flame failure.

A piping arrangement with separate suction and return lines between tank and burner. It is preferred where the tank is below the burner or the run is long, and it returns unused oil to the tank.

A storage tank supported on brackets or legs above the floor, typically in a basement. It must be properly supported, vented, and protected from physical damage and corrosion.

The fill connection and the vent pipe that lets air escape as the tank fills and admits air as fuel is drawn. Undersized, blocked, or improperly sloped vents cause spills and dangerous tank pressure.

A float-type indicator that shows approximate tank contents. It is a rough guide only, so technicians confirm level with a dipstick or by measuring and should never rely on it for precise delivery figures.

Devices that trap dirt and sludge before it reaches the pump and nozzle. A clogged filter reduces pressure and flow, causing lockouts, and is one of the first items to check on a no-heat call.

A thermostat that switches 120 or 240 volts directly to the burner circuit rather than using a low-voltage relay. Wiring and replacement must follow the correct circuit, since line voltage is present at the device.

A safety control on steam and hot-water boilers that stops the burner if water level falls too low. It protects the heat exchanger from overheating and is tested regularly for proper operation.

A temperature-operated control on a boiler that starts and stops the burner and may also control circulators. Settings include high limit, low limit, and differential, which determine how the boiler responds to load.

A motorized valve that opens or closes to direct hot water to one heating zone. End switches in the valve often start the circulator or burner, so a stuck valve can cause a no-heat complaint in one area only.

The pump that moves hot water through the piping and heat emitters. Air binding, a failed capacitor, or a stuck impeller commonly shows up as uneven heat or a boiler that runs but does not satisfy the thermostat.

A test instrument that measures voltage, resistance, and often current. Technicians use it to verify power at the primary control, check cad cell resistance, and confirm transformer output during troubleshooting.