PGDB Certifying Gasfitter key terms

The air deliberately supplied to an appliance burner so fuel gas can burn completely and safely. It must be calculated separately from dilution and ventilation air and kept free of obstruction.

Air mixed with fuel gas before it reaches the burner ports, setting the initial air-to-gas ratio and shaping the flame. Too little produces a lazy yellow flame; too much can lift or light off poorly.

Air supplied beyond the chemically ideal amount needed for complete combustion. Measured as a percentage during combustion analysis, it dilutes flue products, lowers efficiency, and is indicated by higher oxygen readings.

The exact quantity of air theoretically required to burn a given volume of gas completely, with no oxygen or fuel left over. It is the reference point for calculating excess air and flue-gas composition.

The proportion of air to fuel gas entering a burner, expressed by volume or mass. Correct ratio produces a stable flame; deviation causes carbon monoxide, soot, flame lift, or flame roll-out.

The heat released by burning a unit volume of gas. Gross value counts latent heat recovered from condensing water vapour; net value excludes it. Ratings and sizing must use the correct basis.

The ratio of a gas's density to that of air at the same conditions. Natural gas is lighter than air and rises; propane and butane are heavier and settle in low areas, changing leak detection and ventilation strategy.

A number combining heating value and specific gravity that predicts how much heat a burner receives through a fixed orifice. Matching Wobbe index ensures an appliance performs correctly when gas composition changes.

Propane, butane, or a mixture stored as a liquid under pressure. It is heavier than air, has a distinct odour, and requires different orifices, pressures, and ventilation than natural gas.

Selecting the burner jet diameter that delivers the correct gas input at the available manifold pressure. Orifices must match the gas family, heating value, and altitude derating to avoid over- or under-firing.

The gas pressure measured at the appliance manifold, downstream of the appliance regulator, while the unit operates. It is compared with the rating plate value to confirm correct input and flame characteristics.

The gas pressure delivered to the appliance inlet before any appliance regulator acts on it. It must stay within the range stated on the rating plate; excessive pressure can damage controls and cause unsafe firing.

The outlet pressure a regulator settles at when downstream flow stops and the seat closes. A rising lock-up above the allowable limit signals a leaking seat or debris and requires service.

A device that reduces incoming gas pressure to a steady outlet pressure as demand varies. Appliance regulators, service regulators, and line regulators each serve different positions in the system.

A controlled check of piping or appliance gas trains for leaks using air, inert gas, or fuel gas at a specified pressure for a set duration. Results must be recorded and the test medium safely purged afterwards.

A soap-based or approved bubble fluid applied to joints and fittings to reveal escaping gas. Bubbles indicate a leak; the joint must be repaired and retested, never merely wiped clean.

An electronic instrument that senses flammable gas concentration and alarms before a hazardous level forms. It is used for initial surveys and confined spaces, but bubble solution still confirms the exact leak point.

The systematic process of locating escaping fuel gas using odour, detectors, bubble solution, and pressure-drop observation. Findings must be isolated, repaired, and documented before restoring service.

The system that carries flue products from an appliance to outdoors. It must be correctly sized, sloped, supported, and terminated to prevent spillage, condensation damage, and re-entry of combustion products.

The passage or duct through which combustion products travel from the appliance heat exchanger toward the outdoors. Its material, size, and routing must suit the appliance category and temperature.

The pressure difference that moves flue gases along the vent and out of the building. It may be natural, induced by a fan, or mechanical; insufficient draft allows spillage into the space.

A device at the appliance flue collar that limits draft and prevents back-pressure from pushing flue gases into the room. It also dilutes flue products and must never be blocked or modified.

Flue products escaping from the appliance or vent connector into the indoor space instead of going outdoors. It is detected by flame or smoke testing at the draft hood and is a serious carbon monoxide hazard.

Reversal of normal vent flow causing flue gases to enter the building, often from depressurization, blocked flues, or competing exhaust fans. It requires immediate investigation and correction.

A negative pressure condition indoors caused by exhaust fans, dryers, or unbalanced air systems. It can overcome natural draft and pull flue products or soil gases into the living space.

Outdoor air supplied to replace air exhausted by fans, dryers, or ventilation systems. Without adequate make-up air, buildings depressurize and combustion appliances may spill or backdraft.

A colourless, odourless, toxic gas produced by incomplete combustion. It binds haemoglobin far more strongly than oxygen; even low indoor concentrations require investigation and evacuation if alarms sound.

Measuring flue-gas oxygen, carbon monoxide, carbon dioxide, and temperature to verify safe, efficient combustion. Results guide air adjustment, identify CO sources, and document appliance performance after service.

The percentage of unused oxygen remaining in flue gases, indicating how much excess air passed through the burner. It is used with stack temperature to calculate steady-state efficiency.

The percentage of carbon dioxide in flue products, which rises as excess air falls. Comparing it with expected values for the fuel helps confirm complete combustion and correct air settings.

A condition where the flame detaches from the burner ports and burns above them, risking flame failure and unstable ignition. It usually signals excessive primary air or over-firing.

Flame burning backward out of the burner opening instead of into the heat exchanger, often from blocked flue passages or delayed ignition. It is a serious hazard requiring shutdown and inspection.

A lag between gas valve opening and burner light-off, allowing gas to accumulate before it ignites suddenly. Causes include weak ignition, dirty burners, or low manifold pressure and must be corrected promptly.

The components that light the burner, such as a standing pilot, spark igniter, or hot surface igniter, together with flame-sensing controls. Correct operation and proof of flame are essential safety functions.

A probe or rod that detects the presence of flame by sensing current through the ionized flame. A dirty or mispositioned sensor causes nuisance lockouts and must be cleaned or replaced.

A pilot-heated device that generates a small voltage to hold the gas valve open only while flame is proven. A weak or failed thermocouple shuts off the pilot and appliance as a safety response.

A control state in which the appliance stops trying to ignite after failed attempts or a safety trip. The cause must be found and corrected, then the control reset according to the manufacturer's instructions.

A high-efficiency appliance that cools flue gases enough to condense water vapour and recover latent heat. It needs a condensate drain, corrosion-resistant vent material, and correct slope toward the drain.

A structured diagnostic process using symptoms, sequence-of-operation checks, and instrument readings to isolate a fault. It should follow the manufacturer's chart and end with verification testing after repair.

The ordered steps an appliance control follows from a call for heat through ignition, firing, and shutdown. Comparing observed behaviour with the sequence quickly narrows where a fault lies.

Professional interaction that keeps the customer informed, respects their property, and explains findings and options clearly. Good practice includes confirming the work, documenting it, and leaving the site safe and clean.