Energy Safe Victoria

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Flues and ventilation

Adequate ventilation and proper flueing are essential for the safe and efficient operation of gas appliances.

Flues work on the principle that hot air is lighter than the surrounding air, so a flue allows the combustion products out into the open atmosphere, rather than spill out of the draught diverter and into the room.

Many internal domestic gas appliances are designed to operate with one of two common types of flue:

  • An open flue, which is fitted through the ceiling and roof
  • A room sealed flue, which is usually fitted through the wall.

Flue safety

Any discolouration or stains on walls or an appliance casing may be signs of a blocked flue. This could mean combustion products are spilling into the room and there is a risk of carbon monoxide poisoning. The appliance should be turned off immediately until it can be inspected and serviced by a licensed gasfitter.

A licensed gasfitter will ensure your flue is not obstructed or blocked and contains no holes, as these problems can cause flue gases to escape into your house instead of passing safely outside.

The flue cowl must be in good condition, so that it does not collapse into the flue outlet and obstruct escaping gases and must prevent entry of vermin or birds that may obstruct the flue pipe.

Ensure the flue terminal of a room sealed or outdoor appliance is free of plant growth, insect nests or any other obstruction.

Flueless heaters and gas cookers


Ensure a room is adequately ventilated when an unflued appliance is being used.

Gas cookers and unflued gas heaters consume air and release combustion products into the room and can make the room stuffy if there is inadequate ventilation.

Water vapour present in the combustion products can also condense on cold surfaces and may lead to mould growth on walls and ceilings where there is poor ventilation.

Flueless heaters – restrictions

There are restrictions on the installation of flueless heaters operating on Natural Gas in Victoria. Consult with your licensed gasfitter before considering purchasing or installing.

This restriction also applies to new and second-hand flueless heaters imported from interstate and overseas. Cabinet heaters are not permitted (mobile heaters containing an LP Gas cylinder).

Air pollutants

Keep away from toxic gases, as the effect of exposure to air pollutants on your health depends on the type and amount of pollutants to which you are exposed, and can occur immediately at the time of exposure or be delayed.

The most common air pollutants from gas combustion are carbon monoxide (CO) and nitrogen oxides. Young children and people with asthma or other respiratory illnesses, are most at risk from air pollutants.

While water vapour is not regarded as an air pollutant, an accumulation of moisture in the room from heating may lead to the growth of moulds and dust mites, which have the potential to affect health.

Emission levels

Emission levels vary depending on the type of heater, the design of the burner and regular servicing. The level of emissions in a room will vary according to:

  • The use of the room
  • The size of the room compared to the input of the heater
  • The ability of the room’s ventilation to remove or dilute emissions.

General tips for the safe use of flued and flueless appliances

  • Always follow the manufacturer’s instructions,
  • Keep appliance grilles and vents clear of obstructions and free of lint and dust,
  • Ensure room ventilation is adequate,
  • Minimise usage per day – consider a flued appliance where long usage is required,
  • Never use an unflued gas heater in the room where you sleep or in a caravan, and
  • Have your heater serviced before winter.

Contact us

If you have any queries in relation to flues and ventilation, please contact ESV on 03 9203 9700 or by email on