BC Gas Fitter ARD cheat sheet

Manifold gas pressure is measured with a water-column manometer or digital gauge; 1 psi = 27.7 in. w.c., so most appliance pressures (3.5 in. w.c. natural, 10-11 in. w.c. propane) are a small fraction of line pressure.

Natural gas heating value ≈ 1,000 BTU/ft³; propane ≈ 2,500 BTU/ft³. Orifice sizing for propane is smaller because the same heat output needs far less volume.

Clock-meter formula: Input BTU/h = (3600 ÷ seconds per revolution) × cubic feet per revolution × heating value. Use a 1 ft³ dial for small inputs, 2 ft³ dial for larger.

Combustion air: a confined space requires 50 ft³ per 1,000 BTU/h input plus openings sized 1 in² per 1,000 BTU/h (each of two openings) to an unconfined space, or 1 in² per 2,000 BTU/h when connecting to outdoors directly.

A properly adjusted natural gas flame is blue with a slight yellow tip; lifting, floating, or a roaring flame indicates overpressure or excess primary air; yellow sooting tips indicate insufficient primary air or blocked orifices.

Leak testing: pressure test at the greater of 10 in. w.c. or 1.5× working pressure, held long enough to show no drop; use soap solution or electronic detectors, never a flame.

Sediment trap (drip leg) is required at the appliance connection, installed as a tee below the gas inlet with a capped nipple extending downward.

Gas pipe sizing uses the longest-run method with Table values for capacity; add fittings and appliance connectors as equivalent length, and derate capacity for propane and for higher pressure drop.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R. A 120 V circuit drawing 10 A dissipates 1,200 W.

A 15 A circuit is protected at 14 AWG copper minimum; 20 A requires 12 AWG; 30 A requires 10 AWG. Ampacity must equal or exceed the overcurrent device.

Grounding and bonding: the equipment grounding conductor provides a low-impedance fault path so the overcurrent device opens; gas piping must be bonded but never used as a grounding electrode.

Class 2 low-voltage thermostat and control wiring must not be run in the same raceway or box as line-voltage conductors unless the insulation rating and separation rules are met.

A control transformer steps line voltage down to 24 V for gas valves and thermostats; a shorted 24 V circuit typically blows the transformer's integral fuse or the low-voltage fuse on the board.

Motor and blower circuits use a separate branch with overload protection; a run capacitor shifts phase on a PSC motor, and a failed capacitor causes the motor to hum and overheat.

Polarity and neutral: the white grounded conductor terminates on the neutral bar, the green or bare conductor on the ground bar; reversed polarity on a gas appliance can energize the chassis.

Flame rectification: the flame conducts current in one direction between the sensor and burner, producing a microamp DC signal the control module reads to prove flame.

Water heater relief valve opens at 150 psi or 210°F; the T&P discharge must terminate within 6 in. of the floor or outside, and must not be trapped or reduced in size.

Thermal expansion in a closed system (check valve or PRV installed) requires an expansion tank or the T&P valve will weep as water heats.

Backflow prevention: an air gap is the highest protection, followed by an RPZ assembly, then a double check. Hose bibs and boiler fills need vacuum breakers.

Fixture unit sizing: a water closet = 3 fixture units (public) or 2.5 (private); a lavatory = 1; convert total fixture units to pipe size using the demand tables.

Drain slope: 2 in. and smaller drain pipe at 1/4 in. per foot; 3 in. at 1/8 in. per foot minimum. Vent must rise vertically at least 6 in. above the fixture before offsetting.

Water hammer arrestors are required at quick-closing valves; a shock-absorbing air chamber must be sized to the system and installed near the fixture group.

A gas-fired water heater needs a draft hood, a vent connector rising at least 1/4 in. per foot toward the chimney, and clearance to combustibles per the listing.

Cross-connection between potable water and a heating boiler is prevented by a backflow preventer or a double-wall heat exchanger.

Steam pressure and temperature are linked: saturated steam at 0 psig is 212°F; at 15 psig it is about 250°F. Superheated steam follows the superheat tables, not the saturation curve.

A steam trap discharges condensate while holding back steam; thermostatic traps respond to temperature, float-and-thermostatic traps to condensate level, and inverted bucket traps to density.

Steam mains pitch in the direction of flow at 1/8 in. per foot for low pressure and 1/4 in. per foot for high pressure, with drip pockets at low points and before risers.

A Hartford loop keeps the boiler water line from dropping below a safe level by tying the equalizer and return together near the boiler waterline.

Safety valve on a steam boiler is set at or below the MAWP and must discharge to atmosphere with no valve or restriction downstream; it is not a relief valve for the water side.

Steam quality is the mass fraction of vapor in the mixture; wet steam carries entrained droplets that cause water hammer and erosion, so separators and traps are used to dry it.

Pipe expansion: ΔL = L × α × ΔT, with α ≈ 6.5 × 10⁻⁶ in./in.°F for carbon steel; 100 ft of pipe heated 200°F grows about 1.6 in.

Water hammer in steam systems comes from slug flow of condensate; correct with proper pitch, traps, and slow-opening valves, not by increasing pressure.