BC Gas Fitter ARD key terms

The air supplied to a burner that mixes with fuel gas and supports burning. It must be provided from indoors, outdoors, or both in quantities set by code for safe, complete combustion.

Air supplied beyond the theoretical amount needed for complete combustion. It ensures all fuel burns but lowers flame temperature and carries heat up the flue, so it is limited by tuning.

Air that enters a draft hood or draft diverter and mixes with flue products. It cools the exhaust and stabilizes draft, so it is not the same as air used for combustion.

The hot products of combustion leaving an appliance, including carbon dioxide, water vapour, nitrogen, and trace carbon monoxide. It must be vented safely outdoors to prevent poisoning and corrosion.

A device on a draft-hood-equipped appliance that admits dilution air and breaks the effect of chimney draft on the combustion process. It also spills flue products if the vent is blocked.

The escape of flue products from the relief opening of a draft hood into the room rather than up the vent. It signals poor draft, blockage, or an undersized vent and is a carbon monoxide hazard.

A colourless, odourless, toxic gas produced by incomplete combustion. It binds with haemoglobin and can be fatal at low concentrations, so appliances must be adjusted and vented to keep it minimal.

The gas pressure measured at the appliance manifold, downstream of the regulator, while the appliance operates. It is set by the manufacturer and checked with a manometer during commissioning and service.

A device that reduces higher supply pressure to a steady lower pressure delivered to the appliance burner. It compensates for changes in supply pressure and load to keep combustion stable.

The outlet pressure a regulator holds when flow stops and the downstream valve closes. It must not rise enough to over-fire or damage controls when the appliance cycles off.

An instrument that measures low gas or air pressure, commonly a U-tube or digital gauge reading in inches of water column. It is used to set manifold pressure and verify draft.

A unit of low pressure equal to the height of a water column it supports, abbreviated in. w.c. Natural gas manifold pressures are typically a few inches of water column and are measured with a manometer.

The pipe or duct that carries flue products from an appliance to the chimney or vent system. It must slope upward, be supported, and be sized and joined so flue gas cannot leak indoors.

A short drip leg installed at the bottom of a gas piping drop near the appliance. It catches dirt, scale, and moisture so they do not reach the gas valve and burner orifices.

A precisely sized hole, usually a removable brass spud, that meters gas into a burner. Its size is matched to the fuel type and manifold pressure to produce the correct heat input.

The rate of energy delivered to an appliance by burning fuel, usually stated in Btu per hour. It is calculated from gas flow and heating value and compared to the rating plate.

A field test that times gas meter dial movement to measure actual gas flow, then converts it to input in Btu per hour. It confirms whether an appliance is firing at its rated input.

A control that opens and closes the gas supply to the burner in response to the thermostat or safety circuit. It must close tightly and is often combined with a pressure regulator and safety shutoff.

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

A probe, often a flame rectification rod, that detects the presence of a burner flame and proves it to the control module. If no flame is sensed, the gas valve is shut off.

The permanent joining of metallic parts to form an electrically continuous path that ensures electrical continuity and safe conduction. It is required on gas piping to prevent a shock or arc hazard.

A deliberate connection between an electrical circuit or equipment and the earth or a grounded reference point. It limits voltage during faults and stabilizes system voltage for safety.

The conductor that connects the non-current-carrying metal parts of equipment to the grounding system. It provides a low-impedance fault path so overcurrent devices trip quickly.

A fuse or circuit breaker that opens a circuit when current exceeds its rating for a set time. It protects conductors and equipment from overheating and fire caused by overloads or short circuits.

A manually operable device that isolates an appliance or circuit from its power source. It must be located within sight and readily accessible so service work can be done safely.

The normal supply voltage of a circuit, such as 120 or 240 volts, as opposed to low control voltage. Line-voltage work requires de-energizing and verifying before touching conductors.

A reduced control voltage, often 24 volts, used for thermostats and control circuits. It operates relays and gas valves and is safer to work on, but is still a shock and short-circuit source.

A device that changes alternating voltage by magnetic induction, commonly stepping 120 volts down to 24 volts for controls. It must be matched to load and protected against short circuits.

A device that stops reverse flow of water or other fluid into a potable water system. It protects drinking water from contamination by boiler water, chemicals, or cross-connections.

Any actual or potential link between a potable water supply and a source of contamination. It must be eliminated or controlled with backflow protection to keep drinking water safe.

A backflow device that opens to atmosphere when supply pressure drops, breaking a siphon. It is used on hose bibs and some appliance connections but cannot be used under continuous pressure.

A physical separation between a water outlet and the flood level of a fixture or receptacle. It is the most reliable backflow protection because no mechanical parts can fail.

A pressure surge caused by a sudden stop of water flow in a pipe, producing a banging noise and stress on joints. It is controlled with arrestors, slow-closing valves, or proper pipe support.

A closed tank with a captive air charge that absorbs the volume increase of heated water in a closed system. It prevents excessive pressure and protects piping, valves, and the water heater.

A safety valve that opens automatically when pressure reaches a set limit, discharging fluid to a safe location. It protects tanks and piping from overpressure and must never be plugged or capped.

A safety control on a boiler that shuts off the burner when the water level falls below a safe point. It prevents overheating and dry firing that could crack the boiler or cause an explosion.

A device that discharges condensate and non-condensable gases from a steam line or heating unit while holding back live steam. A failed trap wastes energy or causes water hammer and poor heating.

The system that collects condensed steam and returns it to the boiler feedwater supply. Efficient return saves energy and water, and its condition affects boiler operation and chemical treatment.