ACS Domestic Gas Fires & Space Heaters Exam

According to BS 5440-1, what is the minimum acceptable clear internal diameter for a flue serving a natural draught open-flued appliance?

• A75 mm
• B100 mm
• C125 mm
• D150 mm

What is the primary purpose of a flue liner in an existing chimney?

• ATo improve the aesthetic appearance of the chimney.
• BTo prevent birds from nesting in the chimney.
• CTo provide a continuous, gas-tight, and corrosion-resistant passage for combustion produc…
• DTo increase the structural stability of the chimney stack.

When inspecting an existing flue prior to appliance installation, what is a crucial test to perform to ensure its integrity?

• AA smoke test or pressure test.
• BA test of the chimney's external render.
• CA visual inspection of the roof tiles around the chimney.
• DA measurement of the chimney's height above the roof line.

What is the minimum recommended height of a flue terminal above the roof line for a pitched roof, to ensure adequate dispersion of combustion products?

• A300 mm
• B600 mm
• C900 mm
• D1200 mm

Why is it important to ensure adequate air supply to an open-flued appliance?

• ATo cool the appliance components.
• BTo prevent the appliance from overheating.
• CTo ensure complete combustion and safe removal of combustion products.
• DTo reduce the noise level of the appliance.

What is a common consequence of an oversized flue on a domestic gas appliance?

• AIncreased efficiency.
• BImproved aesthetics.
• CReduced flue gas velocity leading to condensation and poor draught.
• DHigher flue gas temperatures.

According to Building Regulations, what material is generally NOT suitable for a flexible flue liner in a masonry chimney serving a gas appliance?

• AStainless steel (316 grade).
• BStainless steel (904 grade).
• CAluminium.
• DFuranFlex.

What is the primary concern when an appliance is connected to a shared flue system?

• AIncreased installation cost.
• BDifficulty in cleaning the flue.
• CRisk of spillage of combustion products from one appliance into another property.
• DReduced aesthetic appeal.

When must a flue be visually inspected internally using a camera or scope?

• AOnly if a blockage is suspected.
• BAs part of every annual service.
• CBefore connecting a new appliance to an existing flue or if a defect is suspected.
• DNever, as it can damage the flue lining.

What is the function of a flue gas analyser when testing a flue system?

• ATo measure the internal diameter of the flue.
• BTo detect the presence of carbon monoxide in the room.
• CTo assess the efficiency of combustion and the composition of flue gases.
• DTo check for leaks in the flue structure.

What is the recommended maximum horizontal length for a section of flue pipe connected to a natural draught open-flued appliance?

• A150 mm
• B300 mm
• C450 mm
• D600 mm

What type of flue system is typically used for a room-sealed condensing boiler?

• AOpen-flued system connected to a traditional chimney.
• BA natural draught twin-wall flue system.
• CA balanced flue or concentric flue system.
• DA single-wall unlined flue pipe.

What is the maximum permissible number of bends (excluding the terminal bend) in a rigid flue system for a domestic gas appliance?

• A2 bends
• B3 bends
• C4 bends
• D5 bends

What is the purpose of a 'notice plate' in relation to a flue installation?

• ATo display the appliance's manufacturer details.
• BTo provide details of the flue system, installer, and date of installation.
• CTo warn occupants about potential carbon monoxide hazards.
• DTo indicate the next service due date for the appliance.

Which of the following conditions is most likely to cause spillage of combustion products from an open-flued appliance?

• AA correctly sized flue.
• BExcessive ventilation in the room.
• CNegative pressure in the room due to extraction fans.
• DA clean and swept flue.

What is the primary risk associated with a flue that is too short?

• AIncreased aesthetic appeal.
• BReduced risk of blockages.
• CInadequate draught and re-entry of combustion products.
• DLower flue gas temperatures.

Which of the following describes a 'Class I' flue system?

• AA room-sealed flue system where air for combustion is drawn from outside.
• BA system where flue gases are expelled directly through a wall terminal.
• CA traditional masonry chimney or a factory-made metal chimney, requiring a lining.
• DA balanced flue system with concentric pipes.

What is the consequence of inadequate insulation around a metal flue passing through a cold space (e.g., an unheated loft)?

• AIncreased flue gas velocity.
• BImproved flue performance due to cooling.
• CRapid cooling of flue gases, leading to condensation and poor draught.
• DReduced risk of fire.

What minimum clearance is typically required from combustible materials for a single-wall metal flue pipe serving an open-flued gas appliance?

• A25 mm
• B50 mm
• C75 mm
• D100 mm

When installing a new gas appliance, how should a chimney that previously served a solid fuel appliance be prepared for use with gas?

• AIt can be used directly without modification.
• BIt must be thoroughly swept, inspected, and likely lined with a suitable flexible or rigi…
• CIt only needs a visual check from the outside.
• DIt should be capped off and not used for gas appliances.

Why is a gas rate test carried out when commissioning a domestic gas fire?

• ATo confirm the appliance's heat input matches the manufacturer's data plate.
• BTo measure the temperature of the flue gases.
• CTo check the colour of the ceramic radiants.
• DTo test the operation of a room thermostat.

Which calorific value is used when gas rating a natural gas appliance by the meter?

• A38.76 MJ/m3
• B20 MJ/m3
• C93 MJ/m3
• D8.76 MJ/m3

When gas rating a fire by the meter, over what period is the standard timed meter reading usually taken, with all other appliances off?

• A2 minutes
• B10 seconds
• C30 minutes
• D1 hour

Before taking a gas rate reading at the meter, what must the engineer do?

• ATurn off all other gas appliances so only the fire is consuming gas.
• BTurn on all other gas appliances to load the meter.
• CDisconnect the gas meter from the supply.
• DCap off the flue terminal.

How is the burner operating pressure of a gas fire verified during commissioning?

• AWith a manometer connected to the appliance pressure test point, compared to the data pla…
• BBy measuring the flue gas temperature with a probe.
• CBy weighing the appliance before and after firing.
• DBy timing the duration of the ignition spark.

What is the maximum permissible pressure drop across the installation pipework between the meter and a natural gas appliance?

• A1 mbar
• B5 mbar
• C10 mbar
• D0.1 mbar

What test must be completed on the gas installation before commissioning a newly connected gas fire?

• AA let-by and tightness test on the installation pipework.
• BA flue gas analysis of the burner only.
• CA water pressure test of the pipework.
• DAn electrical earth loop impedance test.

An open-flued gas fire's permanent air vent free area is calculated from the net heat input in excess of which value (BS 5440-2)?

• A7 kW
• B3 kW
• C12 kW
• D70 kW

For an open-flued domestic gas appliance, how much permanent ventilation free area is required per kW of net heat input above 7 kW (BS 5440-2)?

• A5 cm2
• B1 cm2
• C20 cm2
• D50 cm2

Why is a spillage test an essential part of commissioning an open-flued gas fire?

• ATo confirm the products of combustion clear up the chimney and do not spill into the room.
• BTo measure the gas consumption rate at the meter.
• CTo set the burner operating pressure.
• DTo test the piezo spark generator.

On commissioning a radiant/convector gas fire with an aerated burner, what does correct combustion typically look like?

• AStable, well-defined blue flames with clear inner cones.
• BLarge smoky yellow flames depositing soot.
• CFlames lifting and detaching from the burner ports.
• DNo visible flame at the burner at all.

Why does a decorative fuel-effect (DFE) gas fire deliberately burn with luminous yellow flames, unlike an aerated burner?

• ATo create a realistic 'live flame' appearance; because of the higher products of combusti…
• BBecause yellow flames always mean dangerous CO, so the fire should be condemned.
• CBecause the gas rate has been set far too low.
• DBecause the primary air shutter has been left fully open.

During commissioning, which check confirms that the operating controls of a gas fire function correctly?

• AVerifying the appliance ignites, the flame-failure device holds in, and the rate control…
• BChecking the paint finish on the control knob.
• CMeasuring only the floor area of the room.
• DConfirming the warranty card has been completed.

What test is carried out on the chimney before the appliance spillage test, to confirm the flue is clear and pulling?

• AA flue flow test using a smoke pellet to confirm the chimney draws and is not blocked.
• BA tightness test on the burner manifold.
• CA gas rate test at the meter.
• DAn insulation resistance test on the wiring.

When checking combustion performance, a CO/CO2 ratio within the appliance's permitted limit indicates what?

• ASafe, acceptable combustion with carbon monoxide kept within limits.
• BDangerous incomplete combustion requiring immediate shutdown.
• CThat the chimney is completely blocked.
• DThat the gas supply pressure is far too high.

When installing an inset gas fire into a builder's opening, which component seals the opening and helps ensure correct flue performance?

• AA correctly fitted and sealed closure (sealing) plate.
• BA flexible rubber gas hose.
• CA central heating expansion vessel.
• DA draught excluder strip on the room door.

During commissioning of an open-flued fire, why must any extract fans in the property be operated while carrying out the spillage test?

• ABecause fans can depressurise the room and cause spillage; testing with them running chec…
• BBecause extract fans increase the appliance's gas rate.
• CBecause fans are required to ignite the appliance.
• DBecause fans are needed to cool the manometer.

Which source gives the correct burner pressure and heat input figures to verify a gas fire against during commissioning?

• AThe appliance manufacturer's installation instructions and data plate.
• BThe customer's most recent gas bill.
• CThe local weather forecast.
• DThe property's electricity meter reading.

Why should the gas supply to a newly connected gas fire be purged before commissioning?

• ATo remove air from the pipework so the burner lights safely and reliably.
• BTo increase the calorific value of the gas.
• CTo cool the burner before firing.
• DTo clean soot from the radiants.

On completing commissioning of a gas fire, what must the engineer do for the customer?

• ADemonstrate safe operation and leave the manufacturer's user instructions with the applia…
• BRemove the user instructions to prevent the customer tampering.
• CDisconnect the carbon monoxide alarm.
• DSeal the room air vents to improve efficiency.

In the context of domestic gas fires and space heaters, what does the safety device 'ASD' refer to?

• AAn Atmosphere Sensing Device (an oxygen-depletion sensing pilot).
• BAn Aspirating Smoke Detector.
• CAn Automatic Shutdown Damper.
• DAn Audible Sounder Device.

How does an oxygen-depletion system (ODS/ASD) pilot make a flueless gas heater safe?

• AAs room oxygen falls, the pilot flame lifts away from the thermocouple, cutting the flame…
• BIt sounds an electronic siren while leaving the gas flowing.
• CIt increases the gas rate to burn off carbon monoxide.
• DIt automatically opens an extra air vent in the wall.

Which type of domestic appliance is required to be fitted with an atmosphere sensing device (ODS)?

• AA flueless gas space heater / flueless gas fire.
• BA room-sealed (balanced flue) condensing boiler.
• CAn open-flued gas fire on a Class 1 chimney.
• DA central heating circulating pump.

A thermocouple used in a gas fire flame-supervision device typically generates an output in which range when heated by the pilot flame?

• AMillivolts (around 20-30 mV).
• B230 volts AC mains.
• CSeveral hundred volts DC.
• DKilovolts.

What is the primary purpose of a flame-supervision device (FSD) on a gas fire?

• ATo shut off the gas to the burner if the flame is not established or is lost.
• BTo increase the heat output of the fire.
• CTo re-light the pilot automatically every hour.
• DTo filter the products of combustion before they enter the flue.

How does a thermoelectric flame-supervision device hold the gas valve open?

• AThe heated thermocouple energises an electromagnet that holds the safety valve open; if t…
• BMains electricity holds a solenoid open continuously.
• CGas pressure alone holds the valve open with no flame sensing.
• DA mechanical spring permanently latches the valve open.