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Open-flued gas space heaters

Important safety information about open-flued gas heaters and ventilation.

Open-flued gas heaters and ventilation

ESV and the Victorian Building Authority (VBA) recommend all gas water heaters, space heaters and central heaters are serviced at least every two years by a qualified gasfitter endorsed to carry out Type A Gas Appliance service work.

Find your local registered gasfitter by searching online or via the VBA’sExternal Link website.

  • All registered and licensed gasfitters are issued with a photo ID card that lists the type of work they are allowed to do. All practitioners should carry this ID and you can request to see it at any time.

    Check the qualified gasfitter is endorsed to service Type A gas appliances (their photo ID will include this information) and has the training to detect carbon monoxide spillage.

    You can also check if a gasfitter is licensed or registered online, using the Victorian Building AuthorityExternal Link directory.

  • Search online, the Victorian Building AuthorityExternal Link website or classified ads from your local newspaper.

  • The inspection and maintenance of an appliance is to ensure your gas appliance is maintained in good and safe working order. A service should include:

    • carrying out a visual inspection of the appliance and flue system,
    • conducting a negative pressure and combustion spillage test (CO test),
    • internal cleaning,
    • the repair or replacement of parts, and
    • operating the appliance to ensure it is working correctly and safely.
  • The cost of a service will vary depending on the type of appliance, the gasfitter, the location of the appliance and a range of other factors. The best option is to look online or in your local newspaper and contact a few gasfitters to get a range of prices.

  • Not unless the value of the work exceeds $750. For further information please contact the Victorian Building AuthorityExternal Link .

  • 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.

    Gas space heaters are classified based on how this fluing is achieved. There are three categories for gas space heaters:

    • flueless
    • open-flued, and
    • room sealed.
  • Flueless space 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.

    Indoor flueless space heaters are restricted in Victoria. Regulations prohibit the installation of new indoor flueless space heaters, with the exception that existing LPG flueless space heaters may be replaced in limited circumstances.

    Gas heaters intended for outdoor use only have different requirements. Heaters designed for outdoor use must never be brought indoors, or in an unventilated location like a caravan or tent.

  • Room sealed space heaters, as the name implies, have a combustion circuit that is completely sealed from the living area. All air drawn in for combustion and all products of combustion emitted, are flued outside the room via separate ducts.

    This means ventilation is not required for the living room and room exhaust fans do not affect the safety of the heater. These appliances have a very low risk of adverse combustion products entering the home.

  • Open-flued space heaters draw air from the room to feed the fire and direct combustion products outside via a flue. Inadequate ventilation and use of exhaust fans can draw carbon monoxide (and other exhaust gases) back into the room in certain circumstances.

    Their design means the combustion circuit is exposed to air pressure from within the room at the burner inlet, and at the flue terminal outside. Consequently, factors such as wind or the use of appliances including bathroom exhaust fans can lower the air pressure inside the room, creating a negative pressure environment.

    If the negative pressure is high enough, airflow through the flue may become restricted or in some cases even reversed. If the supply of fresh air to the burner is interrupted, the flame will produce high levels of carbon monoxide.

    To ensure the burner is not affected by changes in the flue, many natural draught open-flued space and ducted heaters are fitted with a draught diverter. The draught diverter is an opening in the flue that allows combustion products to spill into the living area in the event the flue is blocked or there is a negative indoor pressure. When the flue is operating correctly, the hot combustion products travelling up the flue will suck combustion products straight past the draught diverter opening to outside.

    However, when there is a fault the draught diverter is designed to automatically redirect combustion products into the living area without interrupting airflow to the burner and without producing excessive carbon monoxide. Therefore, the room in which the heater is installed requires ventilation to provide replacement air used by the heater, and prevent negative pressures from exhaust fans from affecting the normal operation of the heater.

    Gasfitters are required to test heaters during installation and servicing to ensure they do not spill combustion products and any exhaust fans do not affect the heater.

    To identify whether your gas space or ducted heater is open-flued, you must contact the manufacturer or a qualified gasfitter.

Open-flued space heaters vs room sealed space heaters

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

  • open-flued – fitted through the ceiling and roof
  • room sealed flue – usually fitted through the wall.

Infographic - Open Flue Room Sealed

An infographic about open-flued heaters and room-sealed heaters to help with gas safety. Two diagram-style drawings showing airflow through and out of the heaters is shown, with a stylised drawing of a person reading on a chair between them.
ESV graphic
Infographic - Open Flue Room Sealed

Draw air from the room to feed the fire.
Inadequate ventilation and use of exhaust fans can draw carbon monoxide (and other exhaust gases) back into the room in certain circumstances.

Draw air from outside the house to feed the fire. As they are sealed, exhaust gases are drawn up the flue and dispersed outside.

  1. Air from inside the room is drawn in to feed the fire
  2. Deadly fire exhaust gases should draw up the flue. However, it can leak back into the room via the draught diverter, which protects the burner flames from ind gusts.
  3. Fresh air from outside is drawn in to feed the fire.
  4. The fire exhaust gases are drawn up the flue and safely outside the house.
Download Infographic - Open Flue Room Sealed
  • Some ducted heaters are open-flued and can be affected by negative pressure if there is insufficient ventilation.

    This can apply to ducted heaters where the appliance is installed indoors (for example in a cupboard) and if there is ‘negative pressure’ this can affect the operation of ducted heater. The air ducts around the house that deliver hot air are not affected by the operation of exhaust fans.

    It is recommended that ducted heaters are serviced every two years and during this service a CO test should be conducted at the heating vent outlets in all rooms.

    I have a ducted gas heating system and the unit is outside / inside my roof. Is this an issue?

    No. Ducted heaters installed outside or within roof spaces are not adversely affected by the operation of exhaust fans.

    However, it is recommended these appliances like all other gas appliances are serviced every two years.

    The service should include a CO test at the heating vent outlets in all rooms.

  • For a fireplace using solid fuel (e.g. wood) you should ensure that smoke is drawn into the chimney and discharged to the outside atmosphere even when exhaust fans are in operation.

    For a gas fuelled burner assembly in a fireplace, permanent ventilation should have been installed by the installing gasfitter.

    If in doubt, engage a licensed gasfitter to check that permanent adequate ventilation is installed and the appliance is not adversely affected by the operation of exhaust fans.

  • Carbon monoxide alarms can be a useful back-up precaution, but should not be considered a substitute for the proper installation and maintenance of gas heating appliances.

    If you are considering purchasing one or more carbon monoxide alarms, remember to:

    • select alarms that meet US or EU carbon monoxide standards, including recommendations for use and installation. To identify these alarms, either the packaging or the alarm will indicate that it complies with one of the following standards:
      • UL2034 (US) or
      • EN50291 (EU)
    • select alarms that provide visual and audible alarms indicating when the electrochemical sensor or battery has expired. While these alarms may provide an indication of the presence of carbon monoxide, their effectiveness is limited to the location where they are installed, as carbon monoxide levels elsewhere in the room may vary.


    • if you purchase a hard-wired alarm, it must be installed by a licensed electrician
    • if you are installing a battery operated CO alarm, ensure you follow the manufacturer’s installation instructions which should detail where the alarm should be located.

    Be aware that CO alarms do not work in the same way as smoke alarms.

    Because carbon monoxide is a gas, it forms pools, which could be away from where the alarm is located. Read more:

Date: 22/04/2024 22:19

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The currency and accuracy of this document cannot be guaranteed once printed or saved to a storage device. If in doubt, please check the ESV website for the current version.

Reviewed 21 June 2023

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