Carbon monoxide and gas heating: what every household should know

Carbon monoxide (CO) is a gas produced when fuel burns without enough oxygen. A well-adjusted gas heater with a sound flue sends its combustion products outside. A heater that's dirty, damaged, poorly adjusted or short of air can produce more CO, and a blocked or damaged flue or a cracked heat exchanger can let it into the house.

Energy Safe Victoria's 'Be Sure' campaign warns that all gas heaters can spill carbon monoxide. You can't see it or smell it, and it can make you seriously unwell or kill you. Nothing about the flame or the smell of the room tells you it's there.

Never bring outdoor gas heaters, barbecues or generators inside, or run a car in a garage attached to the house. They produce CO too.

Gas space heaters come in three broad kinds. Room-sealed heaters draw combustion air from outside and send exhaust straight back out, so the room's air isn't part of the burning. Open-flued heaters take combustion air from the room and rely on a flue to carry the exhaust up and away. Flueless heaters release their exhaust into the room.

Energy Safe Victoria says open-flued gas heaters can spill carbon monoxide more easily than other types, which makes them more dangerous. Since 1 August 2022 it has banned the sale of old, unsafe open-flued gas space heaters without safety shutdown features, second-hand ones included.

Gas ducted heaters have their own risk point: the heat exchanger. If it cracks, combustion gases can enter the air blown to every room, which is why a ducted heater service includes a CO test at the outlets.

Victoria's Department of Health says inhaled carbon monoxide replaces oxygen in the blood. Possible symptoms include tiredness, shortness of breath, headaches, dizziness, nausea, weakness, confusion and chest pain.

They're easy to mistake for a winter virus. Clues that point to CO: symptoms that start when the heater is on and ease when you go outside or leave the house, several people or pets affected at once, and symptoms worst in the room with the heater.

If you suspect carbon monoxide, switch the heater off if it's safe to do so, open doors and windows, get everyone outside into fresh air and get medical advice for anyone who feels unwell. If there is smoke, fire or immediate danger, get everyone out. Don't use the heater again until a licensed gasfitter has checked it.

An open-flued heater relies on its flue drawing exhaust up and out. Rangehoods, bathroom and laundry exhaust fans and vented clothes dryers all push air out of the house. If more air leaves than can get in, the house is under negative pressure, and the easiest path for replacement air can be straight down the heater's flue, bringing the exhaust with it.

Energy Safe Victoria advises against running kitchen rangehoods or bathroom exhaust fans while a gas heater is on, because doing so can create negative pressure that draws carbon monoxide into living spaces.

Powerful new rangehoods are a common renovation upgrade. If you have an open-flued gas heater, tell your gasfitter about any new extraction and get their advice before running the two together.

Older homes in suburbs like Altona, Laverton and Hoppers Crossing often have permanent wall vents and draughty windows, and some of those vents are there to give gas appliances air. Sealing them helps comfort, but not before the heating has been checked.

Energy Safe Victoria warns that renovating or weather-sealing a home that still has an open-flued gas heater may change the ventilation needed to clear carbon monoxide from the heater, which could trap dangerous CO inside. Have a licensed gasfitter assess the heater and its ventilation before draught-proofing, replacing windows or closing up vents.

Victoria's coming rental draughtproofing standard, due to apply from 1 July 2027, builds in the same caution: a rental with gas appliances will need a gas safety check before draughtproofing starts, and if the check finds unflued or open-flued appliances, the draughtproofing must not go ahead.

Energy Safe Victoria recommends that all gas heaters be serviced at least every two years by a qualified gasfitter, including a test for carbon monoxide leakage. It says a service should include a visual inspection of the appliance and flue, a negative pressure and combustion spillage test, internal cleaning, repair or replacement of parts, and running the appliance to confirm it works correctly and safely.

In a comprehensive service the gasfitter must use a carbon monoxide analyser to test for spillage, and Energy Safe Victoria advises using a registered or licensed gasfitter who has completed the industry CO training course. For ducted heaters, the CO test should be done at the outlets in every room.

Watch for changes between services too. If anything changes, such as the flame colour, Energy Safe Victoria says a qualified gasfitter should inspect the heater, and it suggests considering replacement if a heater is old or hasn't been serviced for several years.

A CO alarm sounds when carbon monoxide builds up in the air around it. It's a useful backstop in homes with gas heating, but Energy Safe Victoria says an alarm helps and should never replace regular gas heater servicing.

Smoke alarms don't detect carbon monoxide, and CO alarms don't detect smoke; combined units are available. Follow the maker's instructions on placement, test the alarm regularly and replace it by its expiry date. You can fit a plug-in or battery alarm yourself, but Energy Safe Victoria's guidance says hard-wired alarms must be installed by a licensed electrician.

If an alarm sounds, treat it as real: switch off gas appliances if it's safe, open up, get everyone into fresh air, and have the heater checked before it's used again.