Oil Heat (Oil-Fired Heating Systems)
This section covers Oil Heat (Oil-Fired Heating Systems) - the combustion and controls side of oil heating: nozzle and pump selection, ignition, primary controls, draft, and combustion testing. HVAC Excellence tests both calculation items (nozzle flow, input, efficiency) and diagnostic items (delayed ignition, cad cell lockout, smoke/CO2 trade-offs).
Burner setup fundamentals
- Nozzle flow ratings are published at 100 psi. Actual flow scales with the square root of pressure.
- Input BTU/h = nozzle GPH × 140,000 (nominal for No. 2 oil).
- Electrode tips are typically 1/16 in. ahead of the nozzle face with a 1/8 in. gap - always per the burner manufacturer's spec.
- Ignition transformers are typically ~10,000 V secondary; the cad cell drops below roughly 1,600 Ω when flame is proven.
- Overfire draft is typically −0.02 in. w.c.; a barometric damper stabilizes draft.
Combustion targets
- Smoke 0–1 (Bacharach scale), CO2 about 11.5–12.5%, stack temperature as low as possible without condensation.
- Set draft first, then verify smoke, then read CO2. Air is adjusted last.
Worked example
A 0.85 GPH nozzle is rated at 100 psi but the pump is set to 140 psi. Flow = 0.85 × √(140/100) = 0.85 × 1.183 ≈ 1.006 GPH. Input = 1.006 × 140,000 ≈ 140,800 BTU/h. Left at 100 psi, the same nozzle would deliver 0.85 × 140,000 = 119,000 BTU/h - a 15% shortfall that the nozzle stamp alone hides.
Traps that cost marks
- Comparing nozzle sizes without correcting for actual pump pressure.
- Chasing CO2 before the smoke test is clean.
- Setting electrodes to the nozzle instead of the spec sheet.
- Missing delayed ignition/puffback caused by a worn pump cut-off or the wrong spray pattern/angle.
- Taking draft at the breach rather than overfire and treating it as combustion quality.