HVAC Excellence Oil Heat Certification cheat sheet

Oil Heat (Oil-Fired Heating Systems)

• No. 2 heating oil properties: roughly 138,000–140,000 Btu per gallon, flash point about 100–130°F, specific gravity about 0.85, and pour point near 0°F; these values drive nozzle sizing, pump pressure, and tank/filter design.

• Combustion chemistry: stoichiometric air for No. 2 oil is about 14.4 lb air per lb fuel (roughly 1,920 ft³ air per gallon). Target CO2 is about 11.5–12.5% with 0–2 smoke and 4–9% O2; excess air above ~50% wastes heat.

• Nozzle flow varies with the square root of pressure: new gph = rated gph × √(new psi ÷ rated psi). A 1.00 gph nozzle rated at 100 psi delivers about 1.41 gph at 200 psi, so pressure changes must be recalculated, not guessed.

• Standard pump pressures: 100 psi for most residential burners, 140 psi common on some Beckett-style units, 175–300 psi for pressure-atomizing commercial burners. Hollow-cone nozzles suit most retention-head burners; solid-cone suits some low-input designs.

• Electrode settings are burner-specific but typical retention-head values are 1/8–5/32 in. above nozzle centerline, 5/32–3/16 in. ahead of the nozzle face, and 5/32–7/32 in. tip-to-tip. Wrong gaps cause hard starts, delayed ignition, or rumbling.

• Cad cell flame sensing: dark resistance is typically above 20,000 ohms (often 50,000+), and flame resistance falls below about 1,600 ohms. Primary controls lock out when the cad cell stays above roughly 1,600 ohms through the trial-for-ignition period.

• Draft and venting: a typical oil-fired appliance needs about −0.02 to −0.04 in. w.c. overfire draft and −0.02 to −0.06 in. w.c. at the breech. A blocked or undersized flue causes spillage, soot, and CO, so barometric damper settings must be verified after any nozzle or air change.

• Tank and supply rules: supply lines slope toward the burner, tanks above the burner use gravity or a single-line system, and lift exceeding about 8 ft (or long runs) requires a two-line or lift pump. A tank gauge, fusible valve, and listed filter are standard safety items.

• Combustion test sequence: run the appliance to steady state, sample flue gas for CO2/O2, temperature, CO, and smoke, then compute steady-state efficiency (about 85–87% for a clean retention-head burner). Smoke above No. 1 trace or CO above 100 ppm indicates a service problem.