Startup, Combustion Analysis, and Performance Verification
Domain 7, Startup, Combustion Analysis, and Performance Verification, tests commissioning sequence, gas-rate verification, combustion readings, and temperature-rise checks. The exam wants measured proof, not assumptions.
Core rules
- Startup includes leak test, purge, inlet and manifold pressure verification, venting inspection, condensate check, and a call for heat through a complete cycle.
- Clock the gas meter to verify input. For a 1 ft³ dial, Btu/h = 3,600 ÷ seconds per ft³ × heating value. Use actual heating value if known.
- Combustion analysis measures O2 or CO2, CO, stack temperature, and draft. Air-free CO corrects for dilution; compare it to the appliance limit. Typical excess air is 15–50%, but follow the manufacturer.
- Verify temperature rise or hydronic ΔT at steady state. Low ΔT may mean high flow; high ΔT may mean low flow, air, or a dirty heat exchanger.
- Record readings and compare with the rating plate and manufacturer's startup chart.
Worked example
A natural gas boiler with a 1 ft³ meter dial takes 36 seconds per revolution. Input = 3,600 ÷ 36 = 100 ft³/h. At 1,000 Btu/ft³, that is 100,000 Btu/h. If the rating plate says 100,000 Btu/h, gas input is correct; now set manifold pressure and check CO and ΔT.
Traps
- Testing before the appliance reaches steady state.
- Confusing as-measured CO with air-free CO.
- Setting manifold pressure without checking inlet pressure under flow.
- Ignoring altitude, derate, or a meter dial that is not 1 ft³.