Installation, Startup, and Combustion Analysis
Installation, Startup, and Combustion Analysis
This domain tests installation clearances, gas pressure adjustment, airflow verification, and combustion analysis. Startup is not just lighting the burner and leaving. Verify the appliance is level, vented per its listing, condensate trapped and sloped, gas piping purged, and electrical polarity and ground correct.
Measure inlet gas pressure with the appliance running. Set manifold pressure to the nameplate value, typically 3.5 in. w.c. for natural gas and 10–11 in. w.c. for LP, unless the manufacturer specifies otherwise. Then confirm temperature rise and static pressure.
Clocking the meter
Btu/h input = (cubic feet of gas × 3600 ÷ seconds) × heating value. Use the meter dial that makes at least one full revolution.
Worked example
A meter test shows 2.0 cubic feet in 72 seconds with gas at 1,000 Btu/ft3. Input = (2.0 × 3600 ÷ 72) × 1,000 = 100 × 1,000 = 100,000 Btu/h. If the nameplate says 80,000 Btu/h, the input is 25% high. Check manifold pressure, orifice size, and gas heating value before adjusting. Next, measure temperature rise: supply 125°F minus return 70°F = 55°F. If the nameplate range is 35–65°F, the rise is acceptable; if it is 70°F, investigate airflow.
Combustion analysis
Use a calibrated analyzer after the appliance is at steady state. Record O2, CO2, CO, stack temperature, and draft. Air-free CO should be low; rising CO with normal O2 points to a problem such as flame impingement or a cracked heat exchanger. High O2 and low CO2 suggest excess air or a venting issue.
Traps
Do not set manifold pressure before checking inlet pressure. Do not measure temperature rise with a dirty filter. Do not assume the gas heating value is exactly 1,000 Btu/ft3. Do not adjust a gas valve by guesswork; use a manometer and the nameplate.