TSSA Gas Technician 3 (G3) cheat sheet

Natural gas is predominantly methane (CH4); typical Ontario utility-delivered heating value is about 37-38 MJ/m3 (roughly 1,000 BTU/ft3), so appliance input ratings assume that range.

Propane (C3H8) has a heating value near 93-95 MJ/m3 (about 2,500 BTU/ft3) and is roughly 1.5-1.7 times heavier than air; natural gas is about 0.6 times the density of air and rises when released.

Complete combustion: CH4 + 2O2 -> CO2 + 2H2O. Incomplete combustion produces carbon monoxide (CO), a colourless, odourless gas that is toxic by displacing oxygen in blood.

Perfect (stoichiometric) combustion of natural gas needs about 10 volumes of air per 1 volume of gas; excess air is supplied in practice to ensure complete combustion.

The three legs of the combustion triangle are fuel, oxygen and ignition source; removing any one prevents or extinguishes combustion.

Odorant added to natural gas is typically mercaptan (ethyl mercaptan); propane also carries an odorant. A gas smell is a safety signal, not a measure of concentration.

Flame characteristics: a properly adjusted natural gas flame is blue with a slightly soft inner cone; yellow tipping suggests insufficient primary air, while lifting or flashback suggests excess primary air or excessive pressure.

Gas pressure units: 1 inch water column (in. w.c.) = 0.249 kPa; 1 psi = 27.7 in. w.c. = 6.895 kPa. Manifold pressure for natural gas appliances is commonly 3.5 in. w.c. (about 0.87 kPa).

Gas laws: at constant temperature, pressure times volume is constant (Boyle); at constant pressure, volume is proportional to absolute temperature (Charles). These explain why pipe sizing and venting depend on gas density and temperature.

In Ontario, the Technical Standards and Safety Act and the Gas Utilization Code (a regulation under that Act) govern gas work; the TSSA administers licensing and enforcement.

A G3 certificate of qualification permits work only under supervision; independent work on gas appliances and piping requires a higher class (G2 or G1), and the scope of permitted work is defined by regulation.

The Gas Utilization Code sets clearance, ventilation, piping, and appliance installation requirements; manufacturer's certified installation instructions also apply and must be followed.

Before any gas work: locate and identify the gas shut-off, verify the appliance is de-energized, and confirm no ignition sources. Purge and test with an approved leak-detection method, never with an open flame.

Leak testing of new or altered piping is done with air or inert gas at the pressure and duration specified by the Code; soap solution or an approved electronic detector is used to locate leaks.

A gas leak response: evacuate, eliminate ignition sources, do not operate electrical switches, call the gas distributor and emergency services from a safe location; the utility controls the meter/service shut-off.

Carbon monoxide alarms are required in dwellings with fuel-burning appliances or attached garages per the Ontario Fire Code; CO alarms must be located per manufacturer instructions and kept clear of dead air spaces.

Combustion air and clearance requirements protect against spillage of flue gases; a draft hood or draft proving device must not be obstructed, and spillage at the draft hood indicates a venting or air-supply problem.

Documentation: permits, inspection records, and pressure-test records are part of compliant gas work; work must be inspected by the authority having jurisdiction before being placed in service where required.

Approved piping materials include black steel pipe, corrugated stainless steel tubing (CSST) and copper tubing where permitted by the Code; each has specific restrictions (e.g., copper not permitted in some concealed or corrosive locations).

Pipe sizing uses the Code's sizing tables based on total connected load, allowable pressure drop, and equivalent length; each fitting adds an equivalent length (a 90-degree elbow is commonly counted as several feet of straight pipe).

Jointing: steel pipe uses threaded joints with approved pipe dope or PTFE tape applied to male threads only; CSST uses manufacturer-approved fittings and must be bonded per manufacturer and Code requirements.

Support and protection: piping must be supported at Code-specified intervals, protected from physical damage, and sleeved where it passes through masonry or concrete.

Sediment trap (drip leg) is required at the appliance connection to catch debris and moisture; it is installed as a tee with a capped nipple below the appliance inlet.

A manual shut-off valve must be installed upstream of each appliance, accessible, and identified; a union or approved disconnect is provided for servicing.

Purging and leak testing: after assembly, the system is pressure-tested with air or inert gas, then purged of air before gas is introduced; air in the line can cause unsafe ignition or flame failure.

Underground and concealed piping requires approved coatings, sleeving and protection from corrosion; CSST and copper must not be buried or embedded where the Code prohibits it.

Pipe identification: gas piping must be identified (e.g., yellow marking or labelling) where required by the Code; valves and regulators must be accessible and labelled.

Category I appliances are negative-pressure, non-condensing appliances that vent into a vertical chimney or Type B vent; Category IV appliances are positive-pressure condensing appliances requiring listed plastic venting (e.g., PVC/CPVC/PP) per manufacturer instructions.

Vent sizing and height follow the Code and manufacturer tables based on appliance input, vent diameter, and equivalent length; a vent that is too large or too short can cause condensation and spillage.

Draft hoods and draft proving switches protect against backdraft; a spillage test (e.g., flame or smoke at the draft hood) confirms the vent is drawing properly.

Combustion air: appliances in a confined space need two permanent openings (one high, one low) sized per Code based on total input; a single opening may be permitted under specific conditions.

Direct-vent (sealed combustion) appliances take combustion air from outdoors and vent outdoors; they must maintain clearances to windows, doors, and air intakes specified by the manufacturer and Code.

Vent termination clearances: minimum distances from windows, doors, air intakes, grade, and adjacent buildings are specified; a vent must not terminate where flue gases can re-enter the building.

Condensate from condensing appliances must drain to an approved location through a trap per manufacturer instructions; freezing or blocked drains can cause appliance lockout.

Venting a fan-assisted appliance into a masonry chimney requires a listed liner if the chimney is not suitable; a chimney must be inspected for condition and sized for the appliance.

Common venting of multiple appliances requires Code/manufacturer-approved manifold design; appliances must not be common-vented with unlisted combinations.

Appliance installation requires the certified rating plate data (input, manifold pressure, gas type) to match the supply; an appliance rated for natural gas must not be connected to propane without an approved conversion kit.

Manifold pressure is set with a manometer at the appliance regulator; natural gas typically 3.5 in. w.c. and propane typically 10-11 in. w.c., but always follow the rating plate.

Check gas supply pressure with all appliances operating (load test); inlet pressure must be within the appliance's specified range, neither too low (incomplete combustion) nor too high (damage).

Combustion analysis: measure CO, CO2, and O2 in flue gases; a CO reading in the flue above the manufacturer's limit indicates a combustion problem requiring correction.

Ignition systems: standing pilot, intermittent pilot, hot surface ignition (HSI), and direct spark. Servicing includes cleaning flame sensors, checking thermocouples, and verifying ignition sequence.

Thermocouple/thermopile testing: a thermocouple generates millivolts when heated; low output causes pilot dropout. Flame sensors must be clean and positioned in the flame for reliable sensing.

Gas valve and regulator servicing: verify inlet and outlet pressures, check for debris, and confirm the valve opens and closes; never bypass safety devices such as the high-limit or spill switch.

After service: leak test all joints, verify venting and combustion air, perform a spillage/combustion check, and confirm the appliance cycles through its full sequence of operation.

Preventive maintenance includes cleaning burners and orifices, checking for corrosion, verifying clearances, and confirming the appliance is listed and installed per manufacturer instructions.