Residential and Light Commercial Appliance Installation and Service
This domain tests the everyday work: furnaces, boilers, water heaters, ranges, dryers and fireplaces installed to the listing, vented correctly and commissioned with measured data rather than assumption.
Location and clearances
- Install to the rating plate and certified instructions: clearances to combustibles, alcove or closet listing, service access, and a noncombustible base where required.
- In a garage, ignition sources must be at least 18 in. above the floor and the appliance protected from vehicle impact.
- Avoid locations with corrosive vapours (pool chemicals, dry cleaning) unless the appliance is listed for them; provide access for burner and flue cleaning.
Connections
Listed connector within length limits, manual shutoff, union, sediment trap, electrical bonding, and a condensate disposal arrangement for condensing appliances that is trapped, sloped and neutralized as required. Water heaters need a T&P valve with a full-size discharge pipe, and seismic strapping where the jurisdiction requires it. Ranges need the anti-tip device; dryers vent outdoors with no screws through the duct.
Commissioning checks
Inlet and manifold pressure with the burner firing, clocked input at the meter, temperature rise across the heat exchanger, combustion analysis, ambient CO, draft verification, and a leak test on every joint.
Worked example
A furnace rated 100,000 Btu/h input at 80% AFUE delivers 80,000 Btu/h. Measured temperature rise is 38°F against a nameplate range of 40–70°F. Airflow = output ÷ (1.08 × ΔT) = 80,000 ÷ (1.08 × 38) ≈ 1,950 CFM, far above the rated 1,200 CFM. Reasoning: excessive airflow produces a low temperature rise, a cold supply and, in a condensing appliance, a flue temperature low enough to cause corrosion and nuisance trips. The fix is the correct blower tap, not a higher gas pressure.
Altitude
Input is derated about 4% per 1,000 ft (610 m) above 2,000 ft unless the appliance is certified for the altitude or has a field-supplied high-altitude kit.
Traps that cost marks
Running a condensing appliance on existing B-vent; leaving a propane orifice in a natural gas appliance; ignoring a spill at the draft hood; skipping the temperature-rise and combustion checks; and forgetting the altitude derate.