TSSA Gas Technician 1 (G1) cheat sheet

Natural gas is predominantly methane (typically 90-95%); propane (C3H8) and butane (C4H10) are the common LP gases, and all three are colourless and odourless before odorant is added.

Complete combustion of methane: CH4 + 2O2 -> CO2 + 2H2O. One volume of methane needs two volumes of oxygen, which is about 10 volumes of air (air is ~21% O2).

Propane combustion: C3H8 + 5O2 -> 3CO2 + 4H2O; propane requires roughly 24 volumes of air per volume of gas.

Incomplete combustion yields carbon monoxide (CO). CO is colourless, odourless and toxic; it binds haemoglobin far more strongly than oxygen, so even low ppm levels are hazardous.

Heating (calorific) values at standard conditions: natural gas roughly 37-39 MJ/m3 (about 1000-1050 Btu/ft3); propane vapour roughly 93-95 MJ/m3 (about 2500 Btu/ft3); butane vapour roughly 120 MJ/m3.

Relative density (specific gravity) with air = 1.0: natural gas about 0.60-0.65 (rises and vents upward), propane about 1.5 and butane about 2.0 (both sink and pool in low areas).

Flammable limits in air: natural gas roughly 4-15% by volume; propane roughly 2.1-9.5%; butane roughly 1.8-8.4%. Outside those bands the mixture will not sustain ignition.

Pressure units and conversions: 1 psi = 27.68 in. w.c. = 2.31 ft of water; 1 in. w.c. = 0.0361 psi = 249 Pa; 1 kPa = 4.02 in. w.c.

Ideal gas behaviour: P1V1/T1 = P2V2/T2 with absolute pressure and absolute temperature (K = C + 273.15). Gas volume shrinks as pressure rises and expands as temperature rises, which affects clocking and orifice sizing.

In Ontario, the Gas Safety Act and its regulation (O. Reg. 212/01, Gaseous Fuels) plus the CSA B149.1 Natural Gas and Propane Installation Code and B149.2 Propane Storage and Handling Code set the legal requirements; the TSSA administers them.

Work on gas appliances and piping must be performed by or under the direction of a certified gas technician holding the correct class; a G1 holder may work on any size and type of gas appliance and may supervise G2 and G3 holders.

A G2 technician works on appliances up to and including 400,000 Btu/h input; a G3 is limited to specific lower-risk, smaller equipment. Class limits apply to the appliance input rating, not the building.

The Gas Code requires a permit or authorization before installing, altering or replacing gas equipment in most cases; the installer must notify the distributor and arrange inspection as required by the authority having jurisdiction.

Every gas installation must be tested for leaks before being placed in service, and the test method and pressure must match code: typically a pressure test with air, inert gas or gas at a specified pressure for a specified duration, with no drop.

Venting, clearances and combustion air requirements are code-prescribed: appliance clearances to combustible material come from the manufacturer's certified listing and must not be reduced without an approved method.

The code requires that gas appliances be accessible for inspection, servicing and cleaning, and that safety devices such as flame supervision and limit controls not be bypassed or defeated.

Documentation duties: leave the manufacturer's literature with the appliance, record start-up readings (manifold pressure, gas input, temperature rise, CO/CO2), and tag or red-tag unsafe equipment taken out of service.

Code recognises the authority having jurisdiction for local amendments; where the manufacturer's certified instructions and the code differ on a specific installation detail, the more restrictive requirement governs.

Gas input (Btu/h) = gas rate (ft3/h) x heating value (Btu/ft3). Clocking the meter over a timed interval gives actual input; compare it with the appliance rating plate.

For a clocked test, ft3/h = (ft3 metered x 3600) / seconds of test. Example: 2 ft3 in 60 s = 120 ft3/h; at 1000 Btu/ft3 that is 120,000 Btu/h.

Manifold pressure is set to the rating plate value with the appliance firing and, for multi-stage or modulating units, at each stage; natural gas is commonly 3.5 in. w.c. and propane 10-11 in. w.c., but the plate governs.

Temperature rise = supply-air temperature minus return-air temperature, measured after steady operation; a rise above the plate range points to low airflow (dirty filter, blocked coil, wrong blower speed, duct restriction).

Combustion analysis targets: CO2 in the flue around 8-9.5% for natural gas at normal excess air; CO should stay well under 100 ppm air-free in a properly adjusted appliance; O2 typically 4-6%.

Draft measurement: a natural-draft appliance needs a stable negative pressure in the flue (commonly about -0.02 to -0.04 in. w.c. in the vent connector) and a draft hood that relieves stack effect; a blocked flue or spillage is an immediate hazard.

Flame appearance is diagnostic: a sharp blue flame with a defined inner cone indicates good primary aeration; yellow tipping, lifting or a lazy flame suggests wrong orifice, low gas pressure, dirty burner ports or excess primary air.

Service sequence for a no-heat call: confirm gas supply and meter valve position, verify 24 V control power and thermostat call, check ignition sequence and flame sensor signal, then measure manifold pressure and gas input before condemning a component.

A flame sensor reading below the control's threshold (often around 1 microamp or more required) causes short-cycling lockout; clean the sensor rod and check the ground path before replacing the control board.

Pipe sizing uses the longest-run method: measure from the meter or regulator to the farthest outlet, total the connected load in ft3/h, then read the capacity table for the pipe size, material and allowable pressure drop.

Natural gas piping tables in CSA B149.1 are based on a pressure drop of 0.5 in. w.c. for low-pressure systems and on the specific gravity of the gas; propane tables use the propane values.

Typical allowable pressure: natural gas at the meter outlet commonly 7 in. w.c. (range roughly 6-7.5 in. w.c.), with appliance manifold pressure set lower by the appliance regulator.

Black steel pipe is joined by threaded fittings; approved sealant must be applied to the male threads only, leaving the first two threads bare, and the pipe must be reamed and free of cuttings.

CSST and copper tubing require listed fittings and, for CSST, bonding to the electrical grounding system per the manufacturer's instructions and code; copper must not be used where the gas contains more than a trace of hydrogen sulphide.

Every appliance connection needs a manual shutoff valve in the same room and within reach, an approved union or connector, and a sediment trap (drip leg) ahead of the appliance controls where required.

A regulator vent must terminate outdoors in a location protected from rain, snow and blockage, and away from openings, windows and intake air; regulators must be sized for the connected load and inlet pressure.

Leak testing: isolate the section, apply test pressure (commonly 10-15 psi for a short duration on new steel piping, or the code-specified value), and hold with a gauge; soap-bubble test individual joints at operating pressure.

Underground piping requires coated or approved material, cathodic protection considerations, and must be buried at the code-specified depth; a tracer wire and riser protection are commonly required.

Category I appliances are non-condensing, negative-pressure vented and rely on a vertical chimney or vent; Category III is positive-pressure non-condensing; Category IV is positive-pressure condensing (common high-efficiency furnaces).

Combustion air for a confined space is provided by two permanent openings: one near the top and one near the bottom, each sized per code (often 1 in2 free area per 1000 Btu/h for inside air, or per 2000 Btu/h for outside air through horizontal ducts).

For a naturally vented appliance, the vent must terminate above the roof at the code height relative to the roof slope (typically 1 ft above the roof within 10 ft horizontally, and 2 ft above a roof ridge within 10 ft).

A draft hood is a dilution device: it relieves stack effect and downdraft, mixes room air with flue gases, and must not be modified or blocked; a spill switch or blocked-vent safety switch protects against spillage.

Condensing appliances produce acidic condensate (pH around 3-5) that must be neutralised where required and drained through corrosion-resistant pipe with a trap; the flue is typically PVC or CPVC rated for the temperature.

Vent connectors must slope upward toward the chimney at a minimum of 1/4 in. per foot of run, be as short and direct as possible, and be supported; a single-wall connector needs clearance from combustibles per code.

A blocked or undersized flue causes spillage of flue gases into the space, a CO hazard; test with a smoke or flame test at the draft hood and confirm spillage does not occur after several minutes of operation.

Direct-vent appliances draw combustion air from outdoors through a dedicated pipe and vent flue gases outside; the intake and exhaust terminals must respect the manufacturer's and code clearances to windows, doors, meters and other appliances.

Standard 24 V control circuit: R is 24 V hot, C is common, W calls for heat, G runs the indoor blower, Y calls for cooling, and the thermostat closes R to W to start a heating cycle.

Ignition sequence: thermostat calls for heat, induced-draft blower proves via pressure switch, ignition source energises, gas valve opens, flame is proven by the flame sensor, and the blower starts after a timed delay.

The flame sensor (flame rectification) must see a microamp DC signal; a dirty rod, poor ground or cracked insulator causes lockout. The hot-surface igniter draws several amps and is fragile; check resistance against the manufacturer's value.

A pressure switch proves the draft blower is running and the vent is not blocked; it must close before ignition and stay closed during operation. A stuck-closed switch or blocked port causes lockout or a hazardous condition.

Safety devices that must never be bypassed: high-limit switch, rollout switch, flame rollout and blocked-vent switches, pressure switches, and the gas valve's redundant/regulator section.

A rollout switch is a manual-reset device that trips when flame rolls out of the burner box, usually due to a blocked flue, dirty burners or a cracked heat exchanger; it should be investigated, not simply reset.

The high-limit switch is an automatic-reset (or manual-reset on some models) temperature safety that opens the control circuit if the appliance overheats, typically from low airflow; it is not a substitute for proper temperature rise adjustment.

Typical control voltages: 24 V AC for the thermostat and gas valve operator, 120 V AC for the blower and ignition module supply, and low-voltage transformer ratings sized to the connected load.

Diagnose with a multimeter: verify 24 V at the gas valve during a call, check continuity of safety switches in series, and confirm the control board's fault code before replacing parts.