Unflued Gas Appliances - Building Biology
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Unflued Gas Appliances

Unflued Gas Appliances


Gas appliances should be serviced annually by a qualified gas fitter to ensure they don’t release toxic gases into the home.

Warning signs that your gas appliance requires immediate attention are:

  • Yellow / orange flame
  • Excessive condensation in the room where the appliance is installed
  • Sooting or staining on or around your appliance

Unflued and faulty gas appliances such as gas stoves, heaters and internal gas hot water services may emit nitrogen dioxide, sulphur dioxide, carbon dioxide, formaldehyde and carbon monoxide which may cause fatigue and drowsiness as well as flu like symptoms, coughs, colds, headaches, asthma and even death. They can also produce significant amounts of humidity into the indoor air mass which could provide ideal conditions for mould to grow. Unvented kerosene and gas heaters cause an increased humidity and subsequent condensation problems, and the same sort of noxious gases as stoves. The effect is greater because they are used for longer periods of time. It is critical therefore that they only be used when they are adequately vented to the exterior of the building.

Combustion gases such as carbon monoxide, nitrous oxides and sulphur dioxide produced from gas appliances and unflued gas heaters are a health hazard. New energy efficient homes are most at risk if passive ventilation is compromised as these gases can build up to levels that could cause health problems such as asthma. In a survey of 52 dwellings in Sydney, Ferrari et al. (1988) found CO concentrations of 1 – 47 ppm with levels in three dwellings exceeding the NHMRC goal. Steer et al. (1990) found CO generated from cooking appliances exceeded the WHO guideline in a small percentage of kitchens, exceeding 50 ppm in one kitchen where the appliance appeared to be malfunctioning. Exposure of individuals in such environments can be severe with the WHO guideline being exceeded on a daily basis.


Air testing is a complicated procedure that requires a thorough knowledge of the sources of potential gases in and around the building, an understanding of the current exposure standards, and the use of highly technical and expensive equipment. A building biologist will test your home for noxious gases and ultrafine particles and provide you with advice to reduce your exposure levels. For details, click here.


  • Promote passive ventilation. Open windows and doors when gas appliances and wood heaters are in use.
  • Ensure the exhaust fan is on when cooking with gas.
  • Do not idle the car in a garage if it is attached to the home
  • In relation to a wood heater, burn only well dried seasoned wood; ensure the flue is open and kept clear of obstruction.
  • A licensed plumber or gas fitter should install, service and maintain a gas appliance and wood heater on a yearly basis.

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