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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.

Open flue heaters vs room sealed heaters

Many internal domestic gas heaters and 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.

Safety alert – Heritage gas space heater

ESV has issued a safety alert on Vulcan Heritage / Pyrox Heritage gas space heaters.

All Victorians with a Vulcan Heritage or a Pyrox Heritage gas space heater in their home need to get them checked by a qualified gasfitter immediately.

For more information on the safety alert and what to do if your home has one, click here.

Open flue heaters

Open flue heaters are particularly vulnerable and sensitive to the environment they are operating in, including negative pressure or compromised ventilation and /or fluing.

There are complex issues involved in determining the causes and risks of CO spillage . Following recent investigations into open flued gas heaters, ESV believes that open-flued technology is incompatible with newer better sealed, energy efficient homes.

To identify whether your heater is ‘open-flued’ contact the manufacturer or check with your local gasfitter.

ESV’s advice to householders with open flue gas heaters

  • Get your heater serviced and checked for CO spillage as soon as possible.
  • In the meantime, if you have alternative forms of heating use those – especially if you haven’t used your gas heater for a while.
  • At the next opportunity replace the open flued heater with a closed or room seal gas heater or split system.
  • Continue to service your heater at least once every two years.
  • Don’t operate your heater overnight – the risk of CO poisoning will increase if there’s an issue (such a blocked flue) and you are not aware of the symptoms as you are asleep.
  • When operating your heater beware of the symptoms of CO poisoning – even subtle and persistent flu like symptoms
  • Be alert to everyone in the house coming down with the same symptoms – the young, old and vulnerable can be badly affected by CO.

Open flue heaters FAQs

ESV has compiled a list of frequently asked questions regarding open flue heaters and the servicing of gas heaters.

If you have any further queries, contact our Gas technical line at or phone 1800 652 563.

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

Flueless heaters draw combustion air from within the room and emit combustion products back into the same space where the heater is located.

These heaters require ongoing ventilation to external spaces to allow fresh air to fuel the burner and discharge combustion products.


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

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.


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).

General tips for the safe use of flued and flueless appliances

  • Have your heater serviced before winter and at least every two years
  • Do not leave your heater on overnight
  • Ensure room ventilation is adequate
  • Always follow the manufacturer’s instructions
  • Keep appliance grilles and vents clear of obstructions and free of lint and dust
  • 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


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.

Contact us

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