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BC Gas Fitter ARD study materials
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BC Gas Fitter ARD practice questions

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Question 1Gas Fitting

What is the primary function of a gas pressure regulator in a residential natural gas system?

  1. To reduce and maintain a steady delivery pressure Correct answer.
  2. To filter out moisture from the gas
  3. To ignite the appliance burner
  4. To measure the total gas consumed

Explanation

A regulator reduces the higher supply pressure to a stable lower pressure and holds it nearly constant as demand changes. It does this by balancing a spring force against a diaphragm acted on by downstream pressure, so the outlet pressure stays steady. Metering, filtering, and ignition are handled by separate components.

Question 2Gas Fitting

Which gas is commonly used as the reference for setting the heating value of natural gas delivered through a distribution system?

  1. Hydrogen
  2. Propane
  3. Methane Correct answer.
  4. Carbon monoxide

Explanation

Natural gas is predominantly methane, so methane is the reference component used when discussing heating value and combustion characteristics of pipeline gas. Methane has a high heating value per unit volume and clean combustion behavior. The other gases listed are either minor constituents or unrelated fuels.

Question 3Gas Fitting

A technician is checking a gas appliance and finds the flame is lifting off the burner ports and burning noisily. Which condition does this most likely indicate?

  1. Insufficient primary air
  2. Low gas supply pressure
  3. A blocked flue
  4. Excessive primary air Correct answer.

Explanation

Flame lift and noisy, roaring combustion usually result from too much primary air, which makes the flame burn above the ports rather than on them. Reducing excess primary air brings the flame back to the burner. Insufficient air instead causes yellow, lazy flames and carbon formation.

Question 4Gas Fitting

What is the purpose of a drip leg (sediment trap) installed in a gas piping system near an appliance?

  1. To vent excess gas to the outdoors
  2. To collect dirt and condensate before it reaches the controls Correct answer.
  3. To provide a secondary shutoff point
  4. To increase gas pressure to the burner

Explanation

A drip leg is a capped vertical section of pipe that traps dirt, scale, and condensate so they do not enter appliance controls and orifices. It is installed as close as practical to the appliance inlet. It does not change pressure, act as a shutoff, or vent gas.

Question 5Gas Fitting

During a pressure test of new gas piping, which medium is typically used for the test?

  1. Water at high pressure
  2. Air or an inert gas Correct answer.
  3. A mixture of gas and air
  4. Natural gas at full line pressure

Explanation

New or modified gas piping is normally strength- and leak-tested with air or an inert gas such as nitrogen, never with gas or a gas-air mixture. Using air avoids introducing fuel into an untested system. Water is generally avoided because it can corrode piping and is hard to remove.

Question 6Gas Fitting

Which device is designed to shut off gas flow to a burner if the pilot flame is not proven?

  1. A manual shutoff valve
  2. A mercury manometer
  3. A pressure regulator
  4. A thermocouple-operated safety valve Correct answer.

Explanation

A thermocouple or flame-safety device generates a small voltage when heated by the pilot, holding the safety valve open. If the pilot goes out, the voltage drops and the valve closes, stopping gas flow. This prevents unburned gas from accumulating at the burner.

Question 7Gas Fitting

What does a water column (w.c.) measurement of gas pressure represent?

  1. The weight of gas in the pipe
  2. The pressure needed to support a column of water of a given height Correct answer.
  3. The temperature of the gas at the meter
  4. The volume of gas flowing per minute

Explanation

Inches of water column express pressure as the height of a water column that the gas pressure can support. One inch w.c. is a very small pressure, suitable for measuring low appliance manifold pressures. It is a pressure unit, not a measure of volume, weight, or temperature.

Question 8Gas Fitting

Why must gas piping be bonded to the electrical grounding system in many installations?

  1. To allow the pipe to serve as a neutral conductor
  2. To improve the heating value of the gas
  3. To prevent a difference in potential that could cause arcing Correct answer.
  4. To reduce gas pressure in the line

Explanation

Bonding equalizes electrical potential between gas piping and the electrical system so stray currents or lightning surges do not arc across joints. Arcing at a gas connection could ignite leaking gas. Bonding is not intended to carry neutral current or affect gas properties.

Question 9Gas Fitting

A technician measures 3.5 inches w.c. at the manifold of a natural gas appliance rated for 3.5 inches w.c. What does this indicate?

  1. The manifold pressure is correct Correct answer.
  2. The manifold pressure is too low
  3. The manifold pressure is too high
  4. The regulator must be replaced immediately

Explanation

When the measured manifold pressure matches the appliance rating plate value, the pressure is correct and no adjustment is needed. Manifold pressure should always be compared with the manufacturer's specified value. A matching reading confirms proper regulation at that test point.

Question 10Gas Fitting

An appliance is located in a tightly constructed room with no dedicated combustion air opening. What is the most appropriate concern?

  1. The regulator will freeze
  2. The gas will burn too hot
  3. The appliance may be starved of combustion air and spill flue gases Correct answer.
  4. The gas meter will over-register consumption

Explanation

Tight construction can limit the air available for combustion and draft, causing incomplete combustion and possible spillage of flue products into the space. Adequate combustion and ventilation air must be provided per the installation code. The other outcomes are not caused by limited room air.

Question 11Gas Fitting

A gas line is being sized for an appliance. Which factor has the greatest effect on the required pipe diameter for a given flow rate?

  1. The color of the pipe coating
  2. The ambient room temperature
  3. The allowable pressure drop and equivalent length Correct answer.
  4. The appliance manufacturer's brand

Explanation

Pipe sizing depends mainly on the gas flow rate, the allowable pressure drop, and the equivalent length of run including fittings. Longer runs and smaller allowable drops require larger pipe. Pipe color, brand, and room temperature do not drive sizing tables.

Question 12Gas Fitting

What is the main hazard of a cracked heat exchanger in a forced-air furnace?

  1. Increased gas consumption
  2. Premature burner ignition
  3. Flue gases mixing with supply air Correct answer.
  4. Reduced manifold pressure

Explanation

A cracked heat exchanger can allow flue products, including carbon monoxide, to enter the circulating air stream and be distributed through the building. This is a serious health hazard and requires the appliance to be taken out of service. The other effects are not direct results of a cracked exchanger.

Question 13Gas Fitting

A technician observes a yellow, sooty flame on a natural gas burner. Which corrective step is most appropriate first?

  1. Replace the gas meter
  2. Increase the gas supply pressure
  3. Check and adjust the primary air shutter Correct answer.
  4. Reduce the flue size

Explanation

A yellow, sooty flame on natural gas usually indicates insufficient primary air, so the air shutter should be checked and adjusted. After correction, the flame should be blue with a stable inner cone. Raising gas pressure or altering the flue does not address the air-to-fuel ratio.

Question 14Gas Fitting

When clocking a gas meter to determine appliance input rate, which information is needed in addition to the time for a measured volume of gas?

  1. The ambient humidity
  2. The heating value of the gas and the test dial volume Correct answer.
  3. The flue diameter and draft pressure
  4. The appliance's electrical draw

Explanation

Input rate is calculated from the volume of gas used in a measured time and the heating value of the gas. The test dial gives the volume per revolution, and the clocked time gives the rate. Flue size, electrical draw, and humidity are unrelated to this calculation.

Question 15Gas Fitting

What is the function of a vent limiter on a gas pressure regulator?

  1. To measure the flow through the regulator
  2. To prevent the regulator from freezing
  3. To limit the maximum outlet pressure setting
  4. To limit the amount of gas escaping from the regulator vent in the event of a diaphragm failure Correct answer.

Explanation

A vent limiter restricts the escape of gas from the regulator's atmospheric vent if the diaphragm ruptures, reducing the hazard of gas release into the space. It is a safety accessory, not a pressure-setting or measuring device. It also does not prevent freezing.

Question 16Gas Fitting

A gas appliance is installed in a basement and the vent connector slopes back toward the appliance. What problem can this cause?

  1. Higher manifold pressure
  2. Faster burner ignition
  3. Condensate and flue gases spilling into the space Correct answer.
  4. Improved draft and efficiency

Explanation

Vent connectors must slope upward away from the appliance so flue gases and condensate travel toward the chimney. A back slope can trap condensate, restrict flow, and cause spillage of flue products. It does not improve draft or affect manifold pressure or ignition.

Question 17Gas Fitting

Which practice is required when joining threaded black iron gas pipe?

  1. Apply thread sealant to the male threads only, leaving the first two threads bare Correct answer.
  2. Wrap the entire fitting in tape
  3. Use no sealant and rely on tight threads
  4. Apply sealant to the female threads only

Explanation

Thread sealant is applied to the male threads, leaving the first one or two threads bare so excess sealant cannot enter and obstruct the gas passage. Sealant on female threads or excess material can shed into the line. Wrapping the whole fitting is not a proper joint method.

Question 18Gas Fitting

A technician is leak-testing a gas valve train with a soap solution and finds bubbles at a union. What is the correct immediate action?

  1. Tighten or remake the joint and retest Correct answer.
  2. Paint over the joint
  3. Increase pressure to blow the leak clear
  4. Ignore it if the bubbles are small

Explanation

Any bubbles at a joint indicate a leak that must be corrected by remaking or tightening the connection and then retesting. Small leaks can still accumulate gas and become hazardous. Increasing pressure or covering the joint does not repair the leak.

Question 19Gas Fitting

What does the term "lockup pressure" refer to on a gas regulator?

  1. The pressure at which the regulator fully opens
  2. The pressure drop across the valve seat during flow
  3. The outlet pressure at which the regulator closes and stops flow Correct answer.
  4. The maximum inlet pressure the body can withstand

Explanation

Lockup pressure is the outlet pressure at which the regulator closes off and stops flow when demand ceases. It is typically slightly above the flowing outlet pressure. It is not the opening point, the body rating, or the flowing pressure drop.

Question 20Gas Fitting

A gas-fired appliance nameplate lists a manifold pressure of 10 inches w.c. for propane. A technician measures 8 inches w.c. What is the most likely effect?

  1. Excess primary air only
  2. Overfiring and high carbon monoxide
  3. Underfiring and reduced heat output Correct answer.
  4. Correct operation

Explanation

A manifold pressure below the nameplate value delivers less fuel than designed, causing underfiring and reduced heat output. The regulator or supply pressure should be investigated. Overfiring would occur if pressure were above the rating.

Question 21Gas Fitting

Which condition would cause a gas regulator to "breathe" or hunt, producing unstable outlet pressure?

  1. A regulator with the vent piped outdoors
  2. A properly sized regulator with a clean vent
  3. An oversized regulator operating at very low flow Correct answer.
  4. A regulator installed with the arrow pointing downstream

Explanation

An oversized regulator operating near the bottom of its capacity range can become unstable and hunt because the valve seat barely opens. Selecting a regulator matched to the load improves stability. Correct sizing, proper orientation, and outdoor venting support stable operation.

Question 22Gas Fitting

A technician calculates the input rate of a furnace by clocking a 1-cubic-foot test dial for 30 seconds and using a gas heating value of 1000 Btu per cubic foot. What is the approximate input rate?

  1. 120,000 Btu/h Correct answer.
  2. 1,000 Btu/h
  3. 30,000 Btu/h
  4. 60,000 Btu/h

Explanation

One cubic foot in 30 seconds equals two cubic feet per minute, or 120 cubic feet per hour. Multiplying 120 cubic feet per hour by 1000 Btu per cubic foot gives 120,000 Btu/h. The other values result from arithmetic or time-conversion errors.

Question 23Gas Fitting

A gas appliance is installed at an altitude well above sea level where the air is less dense. How should the technician respond to the appliance's combustion air setting?

  1. Follow the manufacturer's high-altitude conversion or derating instructions Correct answer.
  2. Remove the burner orifices
  3. Ignore altitude because gas appliances are unaffected
  4. Increase manifold pressure to compensate

Explanation

At higher altitude, lower air density changes the air-to-fuel ratio, so manufacturers provide high-altitude kits or derating instructions. The technician must follow those instructions to maintain proper combustion. Simply raising pressure or removing orifices would create unsafe overfiring.

Question 24Gas Fitting

A technician finds that a gas appliance's flue gases are spilling from the draft hood during operation. Which combination of causes should be investigated first?

  1. Insufficient draft and blocked venting Correct answer.
  2. A new gas meter and low heating value
  3. Excess primary air and high manifold pressure
  4. Electrical bonding and pipe color

Explanation

Spillage at a draft hood points to inadequate draft or an obstruction in the vent system, such as a blocked flue or undersized chimney. The vent path and draft should be checked before other causes. Air settings and metering do not directly explain draft hood spillage.

Question 25Gas Fitting

Why is it important to verify the clocked input rate against the appliance rating plate rather than relying only on manifold pressure?

  1. Rating plates are often incorrect
  2. Clock timing is always more accurate than pressure
  3. Gas meters measure pressure, not volume
  4. Manifold pressure alone does not confirm the actual fuel flow and heating value delivered Correct answer.

Explanation

Manifold pressure indicates the pressure at the burner but does not by itself confirm the actual volume and heating value of gas delivered. Clocking the meter verifies real input rate, catching issues such as oversized orifices or incorrect gas heating value. Rating plates are authoritative when legible, and meters measure volume, not pressure.

Question 26Gas Fitting

Which unit is used to express the pressure of natural gas supplied to residential appliances in Canada?

  1. Millimetres of mercury
  2. Pounds per square inch
  3. Inches of water column Correct answer.
  4. Kilopascals per litre

Explanation

Residential and light commercial gas pressures are customarily stated in inches of water column, because the pressures involved are small and a water manometer gives a readable, accurate value. One inch of water column equals about 0.25 kPa, so appliance manifold pressures are typically a few inches w.c. Pounds per square inch and millimetres of mercury are used for much higher or much lower pressure ranges.

Question 27Gas Fitting

What colour should the flame of a properly adjusted natural gas burner normally appear?

  1. Green at the base
  2. Deep red throughout
  3. Clear blue with a defined inner cone Correct answer.
  4. Bright orange with yellow tips

Explanation

A correctly adjusted natural gas burner produces a stable, mostly blue flame with a distinct inner cone where primary air and gas mix. Yellow tipping or orange streaks indicate incomplete combustion and insufficient primary air. Green or red colours are not characteristic of normal gas combustion.

Question 28Gas Fitting

Which gas is commonly added to natural gas to give it a detectable odour?

  1. Mercaptan Correct answer.
  2. Nitrogen
  3. Propane
  4. Carbon monoxide

Explanation

Mercaptan, typically ethyl mercaptan, is injected into natural gas so leaks can be detected by smell before concentrations reach dangerous levels. Natural gas itself is essentially odourless. Carbon monoxide, propane, and nitrogen are not added as odorants.

Question 29Gas Fitting

Which type of valve is designed to allow flow in one direction only within a gas train?

  1. Gate valve
  2. Globe valve
  3. Check valve Correct answer.
  4. Butterfly valve

Explanation

A check valve permits flow in a single direction and closes when flow reverses, protecting equipment and preventing backflow in the gas train. Gate, butterfly, and globe valves are manually operated shutoff or throttling devices that do not inherently prevent reverse flow.

Question 30Gas Fitting

What is the purpose of a drip leg (sediment trap) installed at the bottom of a gas supply riser to an appliance?

  1. To collect condensate and debris before it reaches the controls Correct answer.
  2. To increase the gas pressure at the burner
  3. To provide a test point for a manometer
  4. To vent excess gas to the outdoors

Explanation

A drip leg is a capped nipple installed at a low point so that dirt, scale, and condensate settle out of the gas stream instead of fouling the appliance controls. It must be located so debris cannot bypass it into the valve train. It does not change pressure or vent gas.

Question 31Gas Fitting

Which material is commonly used for the flexible connector between a gas manifold and a movable appliance such as a range?

  1. Rigid black steel pipe
  2. Copper tubing without a coating
  3. Corrugated stainless steel tubing connector Correct answer.
  4. PVC pipe

Explanation

A listed corrugated stainless steel connector is flexible, allows the appliance to be moved for cleaning or service, and is rated for gas service. Rigid pipe cannot accommodate movement, PVC is not permitted for gas, and bare copper is restricted and unsuitable for a movable appliance connection.

Question 32Gas Fitting

What is the primary function of the thermocouple in a standing-pilot gas appliance?

  1. To generate a small voltage that holds the safety valve open while the pilot burns Correct answer.
  2. To monitor flue gas temperature
  3. To regulate manifold gas pressure
  4. To ignite the main burner

Explanation

A thermocouple produces a small millivolt signal when heated by the pilot flame, and this signal energizes the safety valve magnet to keep gas flowing. If the pilot goes out, the signal collapses and the valve closes. It does not ignite the burner, regulate pressure, or sense flue temperature.

Question 33Gas Fitting

Why must the gas supply be shut off and the line purged before disconnecting a burner manifold for service?

  1. To prevent air from entering the meter
  2. To reset the appliance's limit switch
  3. To eliminate the risk of gas release and ignition during the work Correct answer.
  4. To increase the flow rate during reassembly

Explanation

Shutting off and purging the line removes fuel from the section being opened, so gas cannot escape into the work area and ignite. A trapped, pressurized line would release gas as soon as the fitting is loosened. Purging also protects the technician from a flash fire when the appliance is relit.

Question 34Gas Fitting

A technician is asked to convert a natural gas appliance to propane. Which component must normally be changed to suit the different fuel?

  1. The ignition transformer
  2. The burner blower motor
  3. The gas valve orifices and regulator spring Correct answer.
  4. The flue thermostat

Explanation

Propane has a higher heating value per cubic foot and requires smaller orifices and a different regulator spring or conversion kit to deliver the correct input rate and manifold pressure. The blower, flue thermostat, and ignition transformer are not fuel-specific in this way. A conversion must follow the manufacturer's listed kit.

Question 35Gas Fitting

A technician measures a pressure drop of 0.8 inches w.c. across a gas valve train at rated flow. What does this indicate?

  1. The meter is undersized for the appliance
  2. The regulator is over-pressurizing the manifold
  3. The appliance is operating at the correct input
  4. There is excessive restriction in the valve train Correct answer.

Explanation

Pressure drop across a valve train reflects resistance to flow; a drop larger than the manufacturer's allowance indicates a restriction such as a clogged screen, undersized valve, or partially closed valve. The manifold pressure itself is measured downstream of the regulator, not inferred from the drop. Excessive drop reduces available pressure at the burner and can lower input.

Question 36Gas Fitting

What is the purpose of the primary air adjustment on an atmospheric gas burner?

  1. To regulate the pilot flame size
  2. To set the secondary air openings at the draft hood
  3. To control the amount of air mixed with gas before combustion Correct answer.
  4. To adjust the manifold gas pressure

Explanation

Primary air is mixed with the gas at the burner before ignition, and the adjustable shutter sets that mixture so the flame is stable and blue. Secondary air is drawn around the flame from the room and is not set by the primary air shutter. Manifold pressure and pilot size are adjusted by separate devices.

Question 37Gas Fitting

A technician must select the correct vent connector diameter for a natural gas furnace. Which reference should be consulted?

  1. The building's electrical panel schedule
  2. The local water utility's pressure chart
  3. The gas meter manufacturer's catalogue
  4. The appliance rating plate and the manufacturer's installation instructions Correct answer.

Explanation

Vent connector sizing depends on the appliance input rating, category, and the manufacturer's listed venting tables and instructions. The rating plate identifies the appliance, and the instructions give the approved vent sizes and configurations. Meter catalogues, electrical schedules, and water charts have no bearing on venting.

Question 38Gas Fitting

A technician is clocking a gas meter with a 2-cubic-foot test dial that makes one revolution in 45 seconds. What is the approximate gas input rate in cubic feet per hour?

  1. 200 cubic feet per hour
  2. 160 cubic feet per hour Correct answer.
  3. 120 cubic feet per hour
  4. 80 cubic feet per hour

Explanation

Input rate equals the dial volume divided by the time in seconds, multiplied by 3600. Here 2 cubic feet divided by 45 seconds equals 0.0444 cubic feet per second, and multiplying by 3600 gives about 160 cubic feet per hour. The result is then compared with the rating plate to confirm correct input.

Question 39Gas Fitting

Why is a manual shutoff valve required immediately upstream of a gas appliance?

  1. To allow the appliance to be isolated for service without shutting down the whole system Correct answer.
  2. To automatically regulate the burner input
  3. To prevent backflow of flue gases
  4. To provide a pressure relief point

Explanation

A dedicated appliance shutoff valve lets a technician isolate the appliance for maintenance or emergency without disturbing other gas users on the system. It is a manual device and does not regulate input, prevent flue backflow, or act as a relief point. The valve must be accessible and identifiable.

Question 40Gas Fitting

What is the main reason for supporting horizontal gas piping at regular intervals?

  1. To improve gas velocity
  2. To allow thermal expansion to escape
  3. To prevent sagging and stress on joints and fittings Correct answer.
  4. To keep the pipe straight for appearance

Explanation

Proper support prevents the weight of the pipe from causing sag, which can strain joints, crack fittings, and create leaks. Support spacing is specified by code and depends on pipe size and material. Supports do not affect gas velocity, and expansion is handled by other means.

Question 41Gas Fitting

A technician finds that a gas regulator's vent is blocked by debris. What is the most likely consequence?

  1. The pilot flame will become larger and noisier
  2. The regulator will deliver uncontrolled or incorrect outlet pressure Correct answer.
  3. The appliance will run cooler than normal
  4. The regulator will deliver higher gas heating value

Explanation

A regulator must reference atmospheric pressure through its vent to control outlet pressure. A blocked vent prevents the diaphragm from responding, so outlet pressure can drift or become erratic and unsafe. Blockage does not change gas heating value, and it typically causes abnormal pressure rather than a cooler or larger pilot flame.

Question 42Gas Fitting

What should a technician do first when arriving at a reported gas odour in a building?

  1. Evacuate occupants and eliminate ignition sources before investigating Correct answer.
  2. Call the gas utility after completing repairs
  3. Open the appliance access panel and start the burner
  4. Light a match to locate the source

Explanation

The first priority with a reported gas odour is life safety: evacuate occupants, avoid creating ignition sources, and notify the gas utility or emergency services. Investigation and repair follow only after the area is made safe. Lighting a match or starting a burner would create an ignition hazard.

Question 43Gas Fitting

Which condition indicates that a gas appliance is experiencing flame rollout?

  1. Condensate dripping from the flue
  2. Flames burning outside the combustion chamber opening Correct answer.
  3. A steady blue flame at the burner ports
  4. A short, quiet pilot flame

Explanation

Flame rollout occurs when combustion gases and flame escape from the burner area instead of travelling up the flue, often because of a blocked flue, poor draft, or a cracked heat exchanger. It is a serious safety hazard requiring immediate shutdown and investigation. A steady blue flame is normal, and condensate is unrelated to rollout.

Question 44Gas Fitting

Why is a combustion air opening sized according to the appliance input rating rather than the room volume alone?

  1. Because air openings only serve the pilot burner
  2. Because larger rooms always require smaller openings
  3. Because input rating determines the flue diameter
  4. Because the amount of air required is proportional to the fuel burned Correct answer.

Explanation

Combustion requires a fixed amount of air per unit of fuel, so the required free area of the opening scales with the appliance input rating. Room volume alone does not guarantee adequate air exchange, especially in tight construction. Flue diameter is a separate venting consideration.

Question 45Gas Fitting

A technician observes that a gas appliance's manifold pressure is correct with the burner off but drops sharply when the burner fires. Which explanation is most likely?

  1. The regulator is failing to maintain pressure under flow Correct answer.
  2. The gas has a higher heating value than expected
  3. The pilot orifice is oversized
  4. The flue is too short

Explanation

A regulator that holds pressure with no flow but cannot maintain it under load is likely defective or undersized, or the supply piping is restrictive. The pressure drop under flow points to a capacity or regulation problem, not to gas heating value, pilot size, or flue length. The regulator and supply piping should be checked.

Question 46Gas Fitting

What is the purpose of a spill switch on a gas appliance equipped with a draft hood?

  1. To ignite the pilot burner
  2. To detect flue gas spillage and shut off the gas supply Correct answer.
  3. To regulate the manifold gas pressure
  4. To measure the gas input rate

Explanation

A spill switch is a temperature-sensing safety device placed near the draft hood that detects hot flue gases spilling into the room and shuts off the gas to prevent carbon monoxide exposure. It does not regulate pressure, ignite the pilot, or measure input. Spillage indicates a venting or draft problem that must be corrected.

Question 47Gas Fitting

A technician is installing a gas appliance in a garage. Which installation practice is most important for safety?

  1. Sealing all combustion air openings
  2. Mounting the appliance so ignition sources are elevated above the floor Correct answer.
  3. Installing the appliance below floor level
  4. Removing the draft hood to improve draft

Explanation

In a garage, gasoline vapours are heavier than air and collect near the floor, so ignition sources must be elevated to reduce the risk of igniting those vapours. Sealing combustion air openings would starve the appliance, and removing the draft hood would defeat safe venting. Installing below floor level would place the appliance closer to heavier-than-air vapours.

Question 48Gas Fitting

A technician calculates an appliance input of 95,000 Btu/h but the rating plate shows 100,000 Btu/h. Which factor should be checked first?

  1. The length of the vent connector
  2. The gas meter calibration and the heating value of the gas supplied Correct answer.
  3. The colour of the pilot flame
  4. The size of the combustion air opening

Explanation

A measured input below the rating plate can result from an inaccurate meter, a lower heating value than assumed, or a restricted supply. The meter calibration and actual gas heating value should be verified before condemning the appliance. Pilot colour, vent length, and air opening size do not directly explain a uniform 5 percent input shortfall.

Question 49Gas Fitting

A technician finds a gas appliance with a manifold pressure above the nameplate value and a flame that lifts off the burner ports. Which corrective action is most appropriate?

  1. Enlarge the burner orifices
  2. Adjust or replace the regulator to restore the specified manifold pressure Correct answer.
  3. Reduce the combustion air opening
  4. Increase the primary air shutter opening

Explanation

High manifold pressure forces excess gas through the orifices, causing flame lift and incomplete combustion, so the regulator must be adjusted or replaced to restore the specified pressure. Enlarging orifices or increasing primary air would worsen the condition. Reducing combustion air would not correct an overpressure problem.

Question 50Gas Fitting

Why does an appliance installed at high altitude often require a derated orifice or adjusted manifold pressure?

  1. Because the gas meter turns faster at altitude
  2. Because gas heating value increases with altitude
  3. Because the flue diameter must be increased
  4. Because lower air density reduces the oxygen available for complete combustion Correct answer.

Explanation

At higher altitude the air is less dense, so each cubic foot of air contains less oxygen, and the appliance must be derated to maintain proper combustion and prevent overheating or incomplete combustion. Heating value does not increase with altitude, and meter speed and flue diameter are not the reason for derating. Manufacturer instructions specify the required derating.