NATE Oil Service flashcards

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

About 140,000 Btu per gallon; used to convert nozzle firing rate into heat output (gph × 140,000 × efficiency).

Weight of a gallon of oil

No. 2 fuel oil weighs about 7.0 lb per gallon at 60°F, with specific gravity near 0.82–0.85.

Degree-day heat estimate

Annual Btu = design heat loss × 24 × heating degree days ÷ design temperature difference, then divided by seasonal efficiency.

Conduction heat loss formula

Q = U × A × ΔT, where U is Btu/(h·ft²·°F), A is area in ft², and ΔT is indoor-outdoor temperature difference.

Water heat capacity

Water requires 1 Btu per pound per °F; at 8.33 lb per gallon, one gallon absorbs about 8.33 Btu per °F rise.

Oil pour point

No. 2 oil typically gels near 0°F to 15°F; below that, wax crystals can block filters and starve the pump.

Steady-state efficiency formula

Efficiency = (stack temperature rise ÷ CO₂) × constant; higher stack rise or lower CO₂ means lower combustion efficiency.

Flue gas dew point

Oil flue gas condenses near 250°F–300°F; net stack temperatures below that range cause acidic condensation and corrosion.

Stoichiometric air for oil

About 14.4 lb of air per lb of No. 2 oil, roughly 1,920 ft³ per gallon; burners run 1.2–1.5× that.

Target CO₂ and smoke

Retention-head burners aim for 11.5–13.5% CO₂ with No. 0–1 smoke; smoke above No. 2 means incomplete combustion.

Nozzle flow vs pressure

Actual gph = rated gph × √(actual psi ÷ 100); a 1.00 gph nozzle at 150 psi flows about 1.22 gph.

Nozzle spray angle selection

Use 70°–80° for most retention-head burners and 45° for narrow chambers; solid cone suits older non-retention chambers.

Electrode gap setting

Set electrode tips about 1/8 in apart and 5/16–7/16 in ahead of the nozzle face to ensure reliable ignition.

Flame retention head function

Swirls combustion air and recirculates hot gas to stabilize ignition; its position and air shutter set CO₂ and smoke.

Delayed ignition causes

Weak ignition transformer, wet oil, or carbon-bridged electrode insulators cause delayed ignition, puffback, and soot.

Overfire draft target

Conventional oil burners aim for about −0.02 in w.c. overfire; flue draft after the barometric damper is −0.02 to −0.06 in w.c.

Tank capacity formulas

Rectangular tank gallons = L × W × H (ft) × 7.48; cylindrical = π × r² × length (ft) × 7.48.

Standard tank usable capacity

A 275-gal oval tank holds about 266 gal; a 330-gal tank about 300 gal; keep fill at 80% or less.

Tank pitch direction

Pitch the tank toward the drain or outlet end at about 1/4 in per foot so water and sludge collect at the low point.

Fuel line sizing rule

Use 3/8 in OD copper for one-pipe runs under about 50 ft; 1/2 in OD for longer runs or two-pipe systems.

One-pipe vs two-pipe

One-pipe uses the bypass plug installed and relies on gravity return; two-pipe removes the plug and returns oil to the tank.

Pump lift limits

Single-stage pumps lift about 8–10 ft; two-stage pumps handle lifts up to roughly 15–17 ft with adequate vacuum.

Maximum pump vacuum

Keep vacuum at the pump under about 12 in Hg (6 in Hg for two-stage); higher vacuum means a restricted line or air leak.

Tank vent requirement

Vent must be at least 1-1/4 in and unobstructed; a plugged vent causes slow fill, pressurization, and spill risk.

Oil filter placement

Install a 10–50 micron filter on the supply line ahead of the pump; a clogged filter causes low pressure and nozzle starvation.

Cad cell flame resistance

Below about 1,600 ohms indicates flame present; above 1,600 ohms (often 10,000+ with no flame) the control locks out.

Primary control lockout timing

After the thermostat call, the control allows 15–45 s for flame detection; no flame in that window causes lockout.

Ignition transformer output

Typical output is 10,000–15,000 V at 10–23 mA; a weak transformer causes delayed ignition and puffback.

High-limit aquastat setting

Breaks the burner circuit at a set high temperature, typically 180°F–200°F on hydronic systems, to prevent overheating.

Low-limit circulator control

Holds the circulator off until boiler water reaches about 120°F–140°F, preventing cold-start condensation and corrosion.

Thermostat wiring basics

On a 24 V heat-only system, R to W calls for heat; C is common; verify 24 V at R and W before diagnosing.

Lockout reset procedure

Correct the fault, then press reset once; repeated resets without diagnosis risk flooding the combustion chamber with oil.