TSSA Gas Technician 2 (G2) key terms

The ratio of a gas's density to the density of air at the same temperature and pressure. Natural gas is roughly 0.60, so it is lighter than air and tends to rise and collect at high points.

The amount of heat released when a unit volume of gas burns completely. In Canada it is usually quoted at standard conditions, and appliances are rated and orifice-sized against a declared value.

A number that combines heating value and specific gravity to describe how much heat an appliance receives through a fixed orifice. Gases with similar Wobbe index can be interchanged without changing burner jets.

The range of gas concentration in air that will ignite. Below the lower limit the mixture is too lean, above the upper limit too rich. Natural gas is roughly 4.5 to 15 percent by volume.

Burning in which all fuel carbon becomes carbon dioxide and all hydrogen becomes water vapour, producing maximum heat and no carbon monoxide. It requires adequate oxygen, mixing and flame stability.

Air supplied beyond the theoretical amount needed for complete combustion. Some excess is needed for safety and mixing, but too much cools the flame and lowers efficiency, raising stack temperature.

A colourless, odourless, toxic gas produced by incomplete combustion. Even low concentrations cause symptoms, so any CO reading in flue gas or room air must be investigated and corrected.

The air supplied to a burner to support burning. It must be drawn from outdoors or from a space large enough to supply the appliance without depressurizing the building or starving other appliances.

Outdoor air introduced to replace air exhausted by fans, dryers or ventilation so that building pressure stays near neutral and appliance venting and combustion are not affected.

A condition where indoor pressure is lower than outdoors, often caused by exhaust fans. It can reverse chimney draft, cause spillage and draw flue products into the living space.

The gas pressure measured at the appliance manifold, downstream of the regulator, while the appliance operates. It is set to the rating plate value and verified with a manometer during commissioning.

The outlet pressure of a gas regulator when flow stops and the valve seats. It is normally slightly above the flowing pressure and must not exceed the appliance's maximum allowable inlet pressure.

A portable instrument that senses combustible gas or carbon monoxide in air and alarms at a set threshold. It is used for leak surveys, purging checks and confined-space entry before work begins.

Displacing air from a pipe or appliance with gas, or displacing gas with air before repair, so that no flammable mixture remains in the system. It must be done to a safe location outdoors.

Releasing gas from a section of piping to atmosphere, usually outdoors through a controlled valve, to empty the line before maintenance or to reduce pressure.

The process by which a jurisdiction adopts a model gas code and adds local amendments. The edition in force, plus the authority having jurisdiction's amendments, governs every installation decision.

The official body or person responsible for enforcing the gas code and approving installations. Where the code is silent or ambiguous, the AHJ's interpretation and permission govern the work.

A published technical standard cited by the gas code, such as appliance, piping or venting standards. Code compliance includes meeting the referenced standards that apply to the equipment installed.

A label from a recognized testing agency showing an appliance or component has been tested to a standard and approved for its intended use. Uncertified equipment normally cannot be installed.

Written authorization from the AHJ to perform gas work. It establishes scope and triggers inspections, and work must not proceed or be concealed until required inspections are complete.

A review by the AHJ of installed work for code compliance, often at stages such as rough-in and final. Failed items must be corrected and reinspected before gas is turned on.

A strength or leak test of piping performed with air, inert gas or gas at a specified pressure for a set duration, with the gauge observed and results recorded before covering or commissioning.

A test of an installed system or joint for gas leakage, using pressure decay on a gauge or a bubble solution on joints. It is required after assembly and before the appliance is placed in service.

A pressure gauge of suitable range and accuracy used for strength and leak tests. The range must be small enough to show the specified pressure drop clearly, and it must be in calibration.

Applying a leak-detection solution to a joint and watching for growing bubbles. It is a simple, reliable check for small leaks on threaded, flanged and compression joints at operating pressure.

Selecting pipe or tubing diameter so that pressure loss at the maximum connected load stays within the code allowance. It depends on gas type, length, load, fittings and allowable pressure drop.

Adding the rated input of every connected appliance, with diversity allowances where the code permits, to determine the total gas demand used for sizing meters, service lines and headers.

The loss of pressure along a piping run caused by friction in pipe, tubing and fittings. The code sets a maximum allowable drop from the meter or regulator to the appliance inlet.

A code table listing capacity for each pipe or tubing size at given lengths and pressure drops. Using the correct table and gas type is essential to a compliant sizing decision.

A capped vertical drop installed at the appliance connection so dirt, scale and condensate fall out of the gas stream before reaching the controls. It must be installed and left accessible.

A listed flexible or semi-rigid connector between the rigid piping and the appliance, of limited length and not concealed. It must be protected from damage and not used to correct misalignment.

A manual shut-off valve at or near an appliance that stops gas flow for service. It must be accessible, listed for gas service and clearly identified so it can be found quickly in an emergency.

Electrically connecting gas piping to the building grounding system so it cannot become energized or act as a conductor. Bonding is required by electrical code and is separate from grounding the pipe itself.

Corrugated stainless steel tubing, a flexible gas piping material. It must be installed per its listing, with approved fittings, protection from damage and the manufacturer's required bonding.

The pipe or duct that carries flue products from the appliance outlet to the chimney or vent. It must be sized, sloped, supported and joined to the vent without reducing the appliance's draft.

The movement of air and flue products through an appliance and vent, created by buoyancy in a chimney or by a fan. Adequate draft removes combustion products and supplies air to the burner.

Flue products escaping from the appliance's draft hood or relief opening into the room instead of going up the vent. It indicates poor draft and is a serious carbon monoxide hazard.

The point where a vent or flue ends outdoors. Location must meet clearance rules from windows, doors, intakes and property lines to keep flue products out of the building and away from people.

An appliance that takes combustion air from outdoors through one pipe and discharges flue products outdoors through another, isolated from indoor air. It is less affected by building depressurization.

A room or enclosure with limited volume relative to appliance input, where the code requires dedicated openings or ducts to supply combustion and ventilation air from outdoors.

The minimum distance an appliance or vent must be kept from combustible material, stated on the rating plate and in the listing. Reduced clearance requires an approved protective assembly.

The manufacturer's label giving model, input rate, gas type, manifold pressure, clearances and venting requirements. It is the primary reference for installation and for verifying correct operation.

Choosing the burner jet diameter that delivers the rated input at the available manifold pressure and gas heating value. Converting between gas types usually requires changing orifices and resetting pressure.

A pressure-measuring instrument, often a U-tube or digital gauge, used to read gas supply, manifold and draft pressures. It is the tool for verifying pressures against the rating plate.

Timing the gas meter dial while the appliance runs to measure actual gas input, then comparing it with the rated input. It verifies orifice sizing, pressure and gas heating value together.

A flame-sensing method where the flame conducts current between an igniter and burner, proving flame to the control. Loss of signal shuts the gas valve within the safety timing.

A device that generates a small voltage when heated by a pilot flame, holding a safety valve open. If the flame is lost, the voltage falls and the valve closes.

A valve that closes automatically on flame failure, power loss or a safety limit trip, stopping gas to the burner. It must be tested for tightness and correct response during servicing.

The electronic module that sequences ignition, proves flame, supervises the burner and locks out on failure. Its timing and retry behaviour must match the appliance's listing.

A control state after failed ignition or flame loss in which gas is shut off and the appliance stops trying until manually reset. Repeated lockouts point to a fault that must be found.

A systematic diagnostic order: confirm the complaint, check gas supply and pressure, verify electrical power and controls, then test ignition, flame and venting before replacing parts.

The regulator that reduces distribution pressure to the pressure delivered to the building's piping. Its outlet setting and lock-up determine the supply available for appliance regulators.

A device or arrangement that limits downstream pressure if a regulator fails, protecting appliances and piping from excess pressure. It may be a relief valve, monitor regulator or vent limiter.