TSSA Gas Technician 3 (G3) key terms

The quantity of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. It is the standard unit for rating appliance input and output capacity in North America.

The total heat released by burning a unit of gas. Gross value counts latent heat recovered from condensing water vapour; net value excludes it, so gross figures are always higher for the same fuel.

The ratio of a gas's density to that of air at the same conditions. Natural gas is lighter than air (about 0.6) and rises when released; propane is heavier (about 1.5) and pools in low areas.

A hydrocarbon fuel stored as a liquid under pressure and vaporized for use. It has roughly 2,500 Btu per cubic foot of vapour, needs more primary air than natural gas, and settles in low spots when leaked.

The rate of heat energy an appliance consumes, usually stated in Btu per hour on the rating plate. It determines gas supply, piping, and venting requirements for the installation.

The gas pressure measured at the appliance burner manifold while the unit operates. It is set by the appliance regulator to the value on the rating plate, typically 3.5 inches of water column for natural gas.

A low-pressure unit used for gas piping and appliance measurements. One inch of water column equals about 0.036 psi, so typical appliance pressures of 3.5 to 11 in. w.c. are a small fraction of a pound.

Selecting the drilled opening that meters gas into a burner so the appliance receives its rated input at the available pressure. Orifices differ for natural gas and propane because of heating value and density differences.

Air mixed with gas before it reaches the burner ports, allowing partial pre-mixing for a stable flame. Too little produces yellow, lazy flames; too much can lift the flame off the ports.

Air drawn from the surrounding space into the flame after the gas leaves the burner, completing combustion. Appliances need an unobstructed supply of it, and venting rules protect that supply.

The visual signs of correct combustion: a steady blue flame with a sharply defined inner cone. Yellow tipping, floating, or roaring flames indicate air, pressure, or orifice problems requiring correction.

A colourless, odourless, toxic gas produced by incomplete combustion. It binds haemoglobin far more strongly than oxygen, so even low concentrations can cause illness or death in a dwelling.

Measuring flue gas oxygen, carbon dioxide, carbon monoxide, and temperature to verify safe, efficient combustion. Results guide adjustments to air shutters and reveal heat exchanger or venting defects.

The air an appliance needs for burning fuel, distinct from dilution or ventilation air. Codes require a permanent, properly sized supply from outdoors or from a space of adequate volume.

A room or enclosure with limited volume relative to appliance input, where normal air infiltration cannot be relied on. Appliances there must have two permanent openings or direct outdoor air connections sized by code.

Air supplied to replace air exhausted by fans, dryers, or other equipment so the building does not depressurize. Without it, vented appliances can backdraft and spill combustion products indoors.

A condition where indoor pressure falls below outdoor pressure, often from exhaust fans or duct leakage. It can reverse chimney draft and pull flue gases into the living space.

The flow of air and combustion products through an appliance and vent caused by pressure difference. Adequate draft carries flue gases outdoors; inadequate or reversed draft is a serious safety hazard.

A device on a draft-hood-equipped appliance that limits chimney draft and relieves pressure so flue gases cannot be pulled through the appliance too fast. It also helps prevent backdraft from entering the burner area.

Escaping of flue products from the draft hood or relief opening into the room instead of up the vent. It signals blocked flues, poor draft, or depressurization and must be corrected before leaving the job.

The pipe or duct carrying flue gases from the appliance to the chimney or vent. It must slope upward, be securely joined, and be kept as short and direct as code permits.

A listed double-wall metal vent with an inner liner and insulating air space, used for venting gas appliances. Its listing specifies clearances, lengths, and fittings, and it must be installed per the manufacturer's instructions.

The passage inside a chimney or vent through which combustion products travel to the outdoors. Flues must be sized for the connected appliances and kept clear of obstructions and debris.

A high-efficiency unit that cools flue gases enough to condense water vapour and recover latent heat. It needs a drain for condensate and often uses PVC or other listed plastic venting.

The minimum distance an appliance or vent must be kept from wood, paper, and similar materials, as stated on the listing label. Reduced clearance can char materials or start a fire.

A short dirt-leg fitting installed below the gas inlet to catch rust, scale, and debris before it reaches the controls. It must be capped and arranged so contaminants settle out of the gas stream.

A vertical length of pipe with a cap at the bottom of a gas line run that collects condensate and debris. It protects downstream regulators and orifices and is drained during servicing.

A manually operated shutoff valve installed in the gas supply line near an appliance. It lets a technician isolate the appliance for service and must be accessible and clearly identified.

A listed flexible or semi-rigid connector joining the house piping to an appliance's inlet. It must be sized for the load, protected from damage, and not pass through walls or floors.

Choosing pipe diameter and length so pressure drop at full demand still leaves adequate pressure at each appliance. Methods use tables based on gas type, specific gravity, load, and allowable loss.

The loss of gas pressure as it flows through pipe, fittings, and valves due to friction. Sizing must keep total drop within code limits so the farthest appliance still receives its required pressure.

A device that reduces incoming gas pressure to a steady lower value for downstream piping or an appliance. It responds to a diaphragm sensing outlet pressure and must be vented and installed per its listing.

The outlet pressure a regulator holds when no gas is flowing. It is slightly higher than flowing pressure and is checked during service to confirm the regulator closes off properly.

A procedure that pressurizes new or altered gas piping with air or inert gas and watches a gauge for a set period. It proves joints are tight before gas is introduced, as required by code.

Applying leak-detection solution to joints and watching for bubbles that indicate escaping gas. It is used on live piping and connections, and open flame must never be used for leak detection.

An electronic instrument that senses gas in the air and alarms before a hazardous concentration forms. Technicians use it to check for leaks and to confirm safe conditions in basements and pits.

The manufacturer's label on an appliance listing model, input rating, gas type, manifold pressure, and clearances. Installation and servicing must match the values shown on it.

A sensor made of two dissimilar metals that generates a small voltage when heated by a pilot flame. That signal holds the gas valve open, and loss of flame closes the valve for safety.

A pilot-heated device of several thermocouples in series that produces enough voltage to power a millivolt gas valve. Weak output from a dirty or misaligned pilot prevents the main burner from lighting.

A small standing flame that ignites the main burner and proves flame presence to the safety control. Its orifice and air openings must be clean and its flame must envelop the sensing element.

A rod or element that detects the presence of flame by sensing current or heat and signals the control to keep the gas valve open. A dirty or corroded sensor causes lockout or short cycling.