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OFTEC Solid Fuel study materials
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OFTEC Solid Fuel practice questions

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Question 1Oil heating installation and maintenance

Which document must be completed and left with the customer after commissioning a new oil-fired boiler installation?

  1. A gas safety record
  2. A boiler commissioning and service record Correct answer.
  3. A building control completion certificate
  4. An Energy Performance Certificate

Explanation

Commissioning an oil appliance requires the installer to complete a commissioning record documenting the installation details, combustion readings and any defects found, and to hand a copy to the customer. Building control and EPC documentation are separate processes handled by other parties.

Question 2Oil heating installation and maintenance

What is the primary purpose of a fire valve in an oil supply line?

  1. To indicate when the tank is empty
  2. To regulate oil pressure at the burner
  3. To filter contaminants from the oil
  4. To shut off the oil supply if a fire occurs Correct answer.

Explanation

A fire valve is a safety device fitted in the oil supply pipe that closes automatically when a fusible element or remote sensor is exposed to excessive heat, stopping fuel feeding a fire. Pressure regulation, filtration and level indication are functions of other components.

Question 3Oil heating installation and maintenance

A two-pipe oil supply system is normally required when the oil tank is positioned in which way relative to the burner?

  1. Immediately adjacent to the boiler
  2. Above the burner with gravity feed
  3. Below the burner level Correct answer.
  4. Inside the same room as the boiler

Explanation

When the tank is below the burner, oil must be drawn up by suction, and a two-pipe system with a return line allows the pump to bleed air and maintain reliable delivery. A tank above the burner can use gravity single-pipe feed.

Question 4Oil heating installation and maintenance

Which flue gas measurement is used to confirm that an oil boiler is burning efficiently and safely?

  1. Water hardness and pH
  2. Oil tank vacuum and line length
  3. Room temperature and humidity
  4. Carbon dioxide and smoke number Correct answer.

Explanation

Combustion analysis on oil appliances uses carbon dioxide (or oxygen) concentration together with smoke number and flue temperature to judge air/fuel ratio and burner setup. The other listed measurements relate to water quality, pipework design or space conditions, not combustion.

Question 5Oil heating installation and maintenance

What does a smoke number reading of zero on a smoke pump test indicate?

  1. The combustion is clean with negligible smoke Correct answer.
  2. The oil pump pressure is too high
  3. The flue is blocked
  4. The burner is over-aerated and flame is unstable

Explanation

The smoke test compares a stain against a scale where zero means no visible smoke, indicating clean combustion. High smoke numbers point to poor atomisation, incorrect air settings or contamination, while a blocked flue or over-aeration would be identified by other readings.

Question 6Oil heating installation and maintenance

Which type of oil is most commonly used for domestic pressure-jet oil-fired boilers in the UK?

  1. Gas oil (Class D)
  2. Lubricating oil
  3. Kerosene (Class C2) Correct answer.
  4. Hydraulic oil

Explanation

Domestic pressure-jet boilers in the UK typically run on kerosene, classified as Class C2, because of its clean burning and suitability for vapourizing and pressure-jet burners. Gas oil (Class D) is used in some larger or older appliances but kerosene is the standard domestic fuel.

Question 7Oil heating installation and maintenance

Before working on an oil-fired appliance, what is the first safety step regarding the fuel supply?

  1. Increase the pump pressure
  2. Open the bleed screw on the pump
  3. Isolate and lock off the oil supply Correct answer.
  4. Remove the flue terminal

Explanation

Safe isolation of the fuel supply, with lock-off where possible, prevents oil being delivered while work is carried out. Adjusting pump pressure, bleeding or removing flue parts before isolation would create a hazard.

Question 8Oil heating installation and maintenance

What is the purpose of the baffles inside the heat exchanger of an oil boiler?

  1. To store heat for later release
  2. To increase turbulence and heat transfer from flue gases Correct answer.
  3. To support the burner nozzle
  4. To filter soot from the flue

Explanation

Baffles slow and turbulate the passage of hot flue gases, improving heat transfer to the water and raising efficiency. They do not store heat, filter soot or support the nozzle.

Question 9Oil heating installation and maintenance

A pressure-jet burner repeatedly locks out shortly after ignition. Which cause should be investigated first?

  1. The radiator valves
  2. The photocell detecting no flame Correct answer.
  3. The room thermostat setpoint
  4. The boiler casing insulation

Explanation

Lockout after ignition commonly indicates the flame detection device, such as a dirty or failed photocell, is not confirming flame. The control then shuts the burner down as a safety measure. Thermostat settings, casing insulation and radiator valves do not cause burner lockout.

Question 10Oil heating installation and maintenance

When setting up an oil burner, what effect does increasing the pump pressure generally have on the spray?

  1. Coarser droplets with a narrower cone
  2. Finer atomisation with a wider cone Correct answer.
  3. No change to atomisation
  4. Complete loss of flame

Explanation

Higher pump pressure forces oil through the nozzle at greater velocity, producing finer droplets and a wider spray angle, which improves combustion if matched to the nozzle rating. Excess pressure can over-fire the appliance, so settings must follow the manufacturer's data.

Question 11Oil heating installation and maintenance

Why should the oil line filter be checked and cleaned during a routine service?

  1. To increase the tank capacity
  2. To raise the flue gas temperature
  3. To prevent restriction and contamination reaching the nozzle Correct answer.
  4. To reduce the boiler water pressure

Explanation

A blocked filter restricts oil flow and allows debris to reach the nozzle, causing poor atomisation and lockouts. Cleaning or replacing the filter element maintains correct supply pressure and protects the burner.

Question 12Oil heating installation and maintenance

A single-pipe gravity oil feed is being installed. What is the minimum acceptable fall along the oil line?

  1. Any fall, provided the pipe is insulated
  2. A rise towards the burner
  3. A continuous fall towards the burner of at least the manufacturer's stated minimum Correct answer.
  4. The line may run level

Explanation

Gravity feed lines must fall continuously towards the burner so that air and oil move forward and airlocks are avoided. The manufacturer specifies a minimum fall, commonly around 1 in 100 or steeper, and level or rising runs are not acceptable.

Question 13Oil heating installation and maintenance

What is the main reason for fitting a de-aerator on a two-pipe oil supply system?

  1. To reduce the flue draught
  2. To remove air from the oil before it reaches the pump Correct answer.
  3. To measure the oil flow rate
  4. To increase the tank's oil temperature

Explanation

A de-aerator separates entrained air from the oil and returns it to the tank, protecting the pump from cavitation and ensuring a steady supply. It does not heat the oil, affect flue draught or act as a flow meter.

Question 14Oil heating installation and maintenance

During a service you find the boiler's flue gas CO2 reading is significantly lower than the manufacturer's figure. What does this most likely indicate?

  1. Excess air and possible over-aeration Correct answer.
  2. Correct combustion
  3. A rich mixture with insufficient air
  4. A blocked oil nozzle

Explanation

A low CO2 reading (with correspondingly high O2) shows too much excess air is entering the combustion process, often through incorrect air damper settings or leaks. A rich mixture would raise CO2 and smoke, while a blocked nozzle would typically cause smoking and instability.

Question 15Oil heating installation and maintenance

Which component controls the oil flow rate delivered to the burner nozzle?

  1. The water pump
  2. The flue thermostat
  3. The room thermostat
  4. The nozzle rating and pump pressure Correct answer.

Explanation

The nozzle's rated output and the pump pressure together determine the oil flow rate and spray characteristics. Flue and room thermostats control operation, and the water pump circulates heating water.

Question 16Oil heating installation and maintenance

Why must the oil storage tank be positioned so that the oil line cannot be subject to excessive suction lift?

  1. To improve the flue draught
  2. To keep the oil cold
  3. To avoid pump cavitation and loss of prime Correct answer.
  4. To increase the tank's static head

Explanation

Excessive suction lift can cause the pump to cavitate and lose prime, leading to unreliable operation and lockouts. Manufacturers specify maximum lift and pipe sizes to keep the suction within safe limits.

Question 17Oil heating installation and maintenance

What is the correct action if a strong smell of oil is detected in a boiler room during a service visit?

  1. Increase the burner air setting
  2. Open the flue terminal
  3. Ignore it as normal for oil appliances
  4. Investigate for leaks and isolate the fuel supply if necessary Correct answer.

Explanation

A strong oil smell indicates a possible leak or spill, which is a fire and environmental hazard. The engineer should investigate the source and isolate the supply if a leak is confirmed, then make safe and report.

Question 18Oil heating installation and maintenance

Which test confirms that the flue is drawing correctly on an open-flue oil appliance?

  1. A smoke number test
  2. A water pressure test
  3. A pump pressure test
  4. A smoke match or pellet draught test at the flue Correct answer.

Explanation

A draught test using a smoke match or pellet at the flue confirms that combustion products are being drawn up the flue and not spilling into the room. Water pressure, smoke number and pump pressure tests assess different aspects of the installation.

Question 19Oil heating installation and maintenance

Which of the following is a correct reason for replacing a burner nozzle during a routine service?

  1. To reset the room thermostat
  2. To increase the flue diameter
  3. To restore correct spray pattern and flow rate Correct answer.
  4. To change the boiler water temperature

Explanation

Nozzles wear and can become partially blocked, altering spray pattern and flow rate, so replacement restores correct combustion. Nozzles have no effect on water temperature settings, flue size or thermostat operation.

Question 20Oil heating installation and maintenance

An oil boiler's flue gas temperature is measured as unusually high with a correct CO2 reading. What is the most likely cause?

  1. A blocked oil filter
  2. A low pump pressure
  3. Fouled heat exchanger surfaces Correct answer.
  4. Excess combustion air

Explanation

With correct CO2, a high flue temperature points to reduced heat transfer, commonly from soot or scale on the heat exchanger surfaces. Excess air would lower CO2, while filter or pressure faults affect fuel delivery rather than flue temperature in this pattern.

Question 21Oil heating installation and maintenance

A two-pipe system is installed with the return line terminating above the oil level in the tank. What problem is most likely to result?

  1. Air being drawn back into the system Correct answer.
  2. Improved pump priming
  3. Reduced fire valve sensitivity
  4. Higher oil pressure at the nozzle

Explanation

The return line should discharge below the oil level so that air separated by the de-aerator is vented to atmosphere without being re-entrained. Terminating above the oil level allows air to be drawn back into the supply, causing instability and lockouts.

Question 22Oil heating installation and maintenance

During commissioning, a pressure-jet burner shows a stable flame but the smoke number rises over successive tests. Which factor is the most probable cause?

  1. A faulty room thermostat
  2. Progressive nozzle fouling or incorrect combustion air setting Correct answer.
  3. Low water pressure in the system
  4. A loose flue terminal

Explanation

A rising smoke number during commissioning suggests the air/fuel ratio is drifting, often from progressive nozzle fouling or an air setting that is too low. Thermostats, water pressure and flue fixings do not cause smoke to increase in this way.

Question 23Oil heating installation and maintenance

Why is it important to check the fire valve's remote sensor position and capillary during a service?

  1. To increase the oil flow rate
  2. To reduce the boiler's noise
  3. To adjust the flue draught
  4. To ensure it operates at the correct temperature and is undamaged Correct answer.

Explanation

The fire valve must sense excessive heat at the correct location and temperature, so the sensor and capillary must be intact and correctly positioned. Damage or misplacement could prevent it from closing in a fire, defeating its safety function.

Question 24Oil heating installation and maintenance

An oil-fired boiler is installed in a room with limited ventilation. What is the main risk if the ventilation opening is undersized?

  1. Incomplete combustion and production of carbon monoxide Correct answer.
  2. Increased boiler water pressure
  3. Faster oil consumption
  4. Reduced flue gas temperature

Explanation

Adequate ventilation supplies combustion air and prevents the room from becoming starved of oxygen, which can lead to incomplete combustion and carbon monoxide production. Water pressure, fuel consumption rate and flue temperature are governed by other factors.

Question 25Oil heating installation and maintenance

What is the correct sequence when commissioning an oil boiler after installation?

  1. Fire the burner, then check oil supply and electrical connections
  2. Set combustion, then connect the oil line
  3. Fill the system, then install the fire valve
  4. Check oil supply and electrical safety, then fire and set combustion Correct answer.

Explanation

Commissioning begins with verifying the oil supply, electrical safety and water fill before firing the burner, after which combustion is set and recorded. Firing before checks or setting combustion before connecting fuel would be unsafe and illogical.

Question 26Oil heating installation and maintenance

Which property of kerosene (Class C2) makes it suitable for use with a pressure-jet burner nozzle?

  1. Its high flash point prevents it from igniting
  2. Its low viscosity allows it to be atomised at normal pump pressures Correct answer.
  3. Its high sulphur content improves flame stability
  4. Its high wax content lubricates the pump

Explanation

Kerosene has a low viscosity and clean burning characteristics, so it atomises readily at the pressures used by pressure-jet burners. High sulphur or wax content would be undesirable, and a high flash point is a storage safety property, not an aid to atomisation.

Question 27Oil heating installation and maintenance

What is the function of the oil control valve (solenoid valve) on a pressure-jet burner?

  1. It opens and closes the oil supply to the nozzle on demand Correct answer.
  2. It filters particles from the oil before the nozzle
  3. It regulates the combustion air damper position
  4. It sets the pump output pressure

Explanation

The solenoid valve is an electrically operated shut-off that admits oil to the nozzle only when the burner control calls for firing. Pump pressure is set by the pressure regulator, air by the damper, and filtration by the in-line filter.

Question 28Oil heating installation and maintenance

Which instrument is used to measure the smoke number of flue gases from an oil burner?

  1. A CO2 analyser
  2. A manometer
  3. A smoke pump and filter paper Correct answer.
  4. A hygrometer

Explanation

Smoke number is assessed by drawing a measured sample of flue gas through filter paper with a hand pump and comparing the stain against a reference scale. Manometers measure pressure, hygrometers humidity, and CO2 analysers measure carbon dioxide content.

Question 29Oil heating installation and maintenance

What does a fire valve on an oil supply line do when its remote sensor is heated?

  1. It shuts off the oil supply to the appliance Correct answer.
  2. It increases oil flow to maintain the flame
  3. It opens a bypass to the tank
  4. It sounds an audible alarm only

Explanation

A fire valve incorporates a fusible or capillary sensor that, when exposed to fire-level temperatures, releases the valve to cut off the oil supply. It does not alarm or increase flow, and a bypass would defeat its purpose.

Question 30Oil heating installation and maintenance

Why is a combustion air supply opening required in the room containing an oil-fired appliance?

  1. To provide oxygen for complete combustion and safe operation Correct answer.
  2. To reduce the flue draught
  3. To dilute the oil in the tank
  4. To cool the boiler casing

Explanation

Combustion needs a continuous supply of air; without adequate ventilation the burner starves of oxygen, producing CO and unreliable firing. Cooling, dilution of fuel, and draught reduction are not the purpose of the opening.

Question 31Oil heating installation and maintenance

What is the purpose of the baffles or turbulators in the heat exchanger of an oil boiler?

  1. To filter soot from the flue gas
  2. To slow the passage of flue gases and improve heat transfer Correct answer.
  3. To support the burner nozzle
  4. To increase the burner's oil pressure

Explanation

Baffles interrupt the gas path so that hot gases linger longer against heat exchange surfaces, raising efficiency. They do not affect pump pressure, filter soot, or support the nozzle.

Question 32Oil heating installation and maintenance

Which symptom most directly indicates that an oil burner nozzle is worn and passing an oversized spray?

  1. The flue draught increases
  2. The pump pressure reads zero
  3. The smoke number rises and CO2 falls with no other change Correct answer.
  4. The burner short-cycles on the thermostat

Explanation

A worn nozzle delivers a coarser, poorly atomised spray, which raises smoke and lowers CO2 because combustion becomes less complete. Short-cycling is a control issue, zero pump pressure indicates a pump fault, and draught is independent of nozzle wear.

Question 33Oil heating installation and maintenance

A pressure-jet burner locks out repeatedly shortly after ignition. Which cause should be investigated first?

  1. The expansion vessel has lost its charge
  2. The boiler thermostat is set too low
  3. The flame detection device is dirty or misaligned Correct answer.
  4. The heat exchanger baffles are worn

Explanation

A lockout immediately after ignition usually means the control cannot confirm flame, so the flame sensor and its alignment are checked first. Baffle wear, thermostat setting, and expansion vessel charge do not prevent flame detection.

Question 34Oil heating installation and maintenance

During a service the flue gas CO2 reading is much lower than the manufacturer's figure. What is the most likely cause?

  1. Excess combustion air Correct answer.
  2. A worn flame sensor
  3. A blocked flue
  4. Too high a pump pressure

Explanation

Low CO2 means the flue gas is diluted with air that did not take part in combustion, typically from excess air or a leak into the flue path. A blocked flue, a worn sensor, and pump pressure do not directly dilute the sample.

Question 35Oil heating installation and maintenance

Which component sets the oil pressure delivered to a pressure-jet burner nozzle?

  1. The nozzle itself
  2. The solenoid valve
  3. The pressure regulator in the pump Correct answer.
  4. The air damper

Explanation

The pump contains an adjustable pressure regulator that sets the delivery pressure to the nozzle. The solenoid valve only opens and closes the supply, the nozzle determines flow at a given pressure, and the damper controls air.

Question 36Oil heating installation and maintenance

Why is it important that the oil line to a burner is not subject to excessive suction lift?

  1. It increases the risk of air and vapour being drawn out of solution, causing unreliable firing Correct answer.
  2. It makes the pump run too fast
  3. It raises the oil temperature in the tank
  4. It increases the nozzle flow rate

Explanation

Excessive negative pressure on the suction side can draw air in through joints and release dissolved gases, leading to erratic firing and pump wear. It does not change pump speed, tank temperature, or nozzle flow in a beneficial way.

Question 37Oil heating installation and maintenance

A strong smell of oil is detected in the boiler room during a service visit. What is the correct immediate action?

  1. Isolate the fuel supply and ventilate before investigating Correct answer.
  2. Increase the burner firing rate to clear it
  3. Continue the service and note the smell
  4. Seal the room and call the fire brigade

Explanation

An oil smell indicates a leak or spill and a fire risk, so the fuel supply is isolated and the area ventilated before any further work or investigation. Continuing work or firing the burner would add ignition risk, and sealing the room traps vapour.

Question 38Oil heating installation and maintenance

Which test confirms that an open-flue oil appliance is drawing correctly?

  1. A pump pressure test
  2. A nozzle flow test
  3. A water pressure test on the system
  4. A smoke test with a match or smoke pellet at the draught diverter Correct answer.

Explanation

A smoke test at the draught diverter shows whether combustion products are being drawn up the flue rather than spilling into the room. Pump, nozzle, and water pressure tests check other parts of the installation.

Question 39Oil heating installation and maintenance

Flue gas temperature is measured as unusually high while the CO2 reading is correct. What is the most likely cause?

  1. A fouled heat exchanger surface Correct answer.
  2. A worn nozzle
  3. A faulty thermostat
  4. An undersized flue

Explanation

With correct CO2, combustion itself is satisfactory; high flue temperature points to poor heat transfer, commonly from soot or scale on the heat exchanger. Nozzle wear would affect CO2 and smoke, an undersized flue affects draught, and a thermostat affects cycling.

Question 40Oil heating installation and maintenance

A two-pipe system has its return line terminating above the oil level in the tank. What problem is most likely?

  1. The tank will overfill
  2. The fire valve will not operate
  3. Air will be drawn into the system, causing erratic firing Correct answer.
  4. The pump will run dry

Explanation

If the return discharges above the oil level, air can enter the return line and be drawn back into the system, causing noisy, unreliable operation. The pump is still fed from the tank, the tank level is unaffected, and the fire valve operates independently.

Question 41Oil heating installation and maintenance

During commissioning, the flame is stable but the smoke number rises with each successive test. What should be done?

  1. Reduce combustion air or check for a fouling cause before re-testing Correct answer.
  2. Increase the pump pressure
  3. Reduce the nozzle size
  4. Ignore it as normal during commissioning

Explanation

A rising smoke number suggests progressive fouling or incorrect air/fuel ratio, so the cause is investigated and the air setting adjusted before re-testing. Increasing pressure or reducing nozzle size changes the fuel input without addressing the cause, and ignoring it is unsafe.

Question 42Oil heating installation and maintenance

Why is the position of a fire valve's remote sensor and its capillary checked during a service?

  1. To measure the oil flow rate
  2. To ensure the sensor will reach fire temperature and shut off the fuel in a fire Correct answer.
  3. To confirm the valve opens at low temperature
  4. To test the pump pressure

Explanation

The sensor must be located where it will be exposed to fire-level heat so the valve operates and isolates the fuel. Its purpose is not to open at low temperature, measure flow, or test pressure.

Question 43Oil heating installation and maintenance

An oil boiler is installed in a room with limited ventilation. What is the main risk if the ventilation opening is inadequate?

  1. The oil will freeze in the tank
  2. The pump will lose pressure
  3. Incomplete combustion may produce carbon monoxide Correct answer.
  4. The boiler will overheat and leak

Explanation

Insufficient air causes incomplete combustion and the production of carbon monoxide, a serious health hazard. Overheating, oil freezing, and pump pressure loss are not the primary consequences of poor ventilation.

Question 44Oil heating installation and maintenance

What is the correct order of steps when commissioning an oil boiler after installation?

  1. Fire the burner, set combustion, then check the oil supply
  2. Check oil supply and electrical safety, set pump pressure, then fire and set combustion Correct answer.
  3. Set combustion, then check oil supply, then fire the burner
  4. Fire the burner, then check oil supply, then set combustion

Explanation

Commissioning begins with verifying the oil supply and electrical safety, then setting pump pressure, before firing and adjusting combustion. Firing before checks risks unsafe operation, and combustion cannot be set before the burner runs correctly.

Question 45Oil heating installation and maintenance

What is the minimum acceptable fall on a single-pipe gravity oil feed line?

  1. About 1 in 10
  2. About 1 in 50
  3. About 1 in 1000 Correct answer.
  4. No fall is required

Explanation

Gravity feed lines need a gentle continuous fall of roughly 1 in 1000 so that any air or gas can travel back to the tank and oil flows freely. Steeper falls are unnecessary, no fall risks air locks, and 1 in 10 is impractical.

Question 46Oil heating installation and maintenance

A burner's flame is yellow and smoky with a correct pump pressure and new nozzle. Which cause is most likely?

  1. A blocked oil filter
  2. A failed flame sensor
  3. Insufficient combustion air or a restricted air path Correct answer.
  4. Excess combustion air

Explanation

A yellow, smoky flame with correct fuel delivery indicates the air side is restricted or the air setting is too low. Excess air would produce a lean flame, a failed sensor would prevent firing, and a blocked filter would reduce fuel rather than cause smoking.

Question 47Oil heating installation and maintenance

Why must a de-aerator be fitted on a two-pipe oil supply system?

  1. To preheat the oil for better atomisation
  2. To remove air and gas from the oil before it reaches the pump Correct answer.
  3. To increase the oil pressure at the nozzle
  4. To filter solid particles from the oil

Explanation

A de-aerator separates entrained air and gas from the oil so the pump receives a solid liquid supply, improving reliability. It does not raise nozzle pressure, filter solids, or heat the oil.

Question 48Oil heating installation and maintenance

An oil-fired appliance shows a stable flame but the flue gas CO reading rises steadily over several minutes. Which action is most appropriate?

  1. Continue running and re-test at the next service
  2. Reduce the nozzle size
  3. Shut down and investigate for a blockage or air restriction Correct answer.
  4. Increase the pump pressure to burn off deposits

Explanation

A rising CO trend indicates incomplete combustion, often from a blocked flue, restricted air, or fouling, and must be investigated immediately. Continuing to run, increasing pressure, or changing the nozzle does not address the hazard.

Question 49Oil heating installation and maintenance

On a pressure-jet oil burner, what is the function of the electrodes and the ignition transformer?

  1. To monitor the flame once combustion is established
  2. To preheat the oil so it atomises more easily
  3. To create the spark that ignites the atomised oil at start-up Correct answer.
  4. To regulate the pump pressure during running

Explanation

The ignition transformer steps up the voltage to produce a high-tension spark across the electrode tips, and this spark ignites the atomised oil spray at start-up. Once the flame is proven, the control box relies on the flame detector rather than the spark to supervise combustion.

Question 50Oil heating installation and maintenance

A pressure-jet burner has a clean nozzle and correct pump pressure, but the pump is drawing oil through a long suction line with several metres of lift and the burner keeps tripping on flame failure. Which cause best explains this?

  1. The flue is too short for the appliance rating
  2. Air is being drawn in through a leaking suction joint, breaking the oil supply Correct answer.
  3. The photocell is positioned too close to the flame
  4. The nozzle is oversized and flooding the combustion chamber

Explanation

Excessive suction lift encourages air to be drawn in at any imperfect joint, and air in the oil line causes an erratic or interrupted spray that leads to flame failure. The supply should be arranged to keep suction lift within limits and all joints airtight.