Every winter, as Sydney’s temperatures drop and heaters fire up across the city, carbon monoxide poisoning becomes a genuine and underreported household danger.
And a question that comes up surprisingly often — especially from homeowners who run both air conditioning and gas heating — is this: can the air conditioner itself be leaking carbon monoxide?
The short answer is no. But the longer answer is far more important — and far more alarming.
Because while your AC unit cannot produce carbon monoxide on its own, it absolutely can circulate it through every room in your home if the conditions are right. And in Sydney homes where gas heating and ducted air conditioning share the same system, those conditions are more common than most people realise.
“Carbon monoxide is known as the silent killer — colourless, odourless, and completely undetectable without a detector. It doesn’t warn you before it becomes dangerous.”
The Truth About Air Conditioners and Carbon Monoxide
Let’s clear up the core question directly — because getting this right matters.
Can an AC Unit Produce Carbon Monoxide?
Why Standard Air Conditioners Cannot Generate CO
Air conditioners cannot create carbon monoxide because they don’t burn fuel to cool your home. In HVAC systems, only gas-powered systems such as furnaces, boilers, and water heaters have the potential to create carbon monoxide.
Carbon monoxide is produced by the incomplete combustion of fossil fuels — natural gas, LPG, wood, petrol.
Your split system or ducted reverse cycle air conditioner runs entirely on electricity and uses refrigerant to move heat. There is no combustion, no fuel burning, and no CO production whatsoever.
So if your air conditioner is the only appliance running, it cannot cause carbon monoxide poisoning.
But Here’s the Real Risk — Circulation
While an air conditioner cannot produce carbon monoxide on its own, it can become susceptible to the outside environment — and if carbon monoxide enters the system from another source, the AC’s blower fan will distribute it throughout the home.
Once CO has slipped into the airstream, your AC’s powerful blower fan takes over. It has one simple job: move air through the ductwork. The fan can’t tell the difference between clean air and poisoned air — so it just does its job, efficiently circulating the toxic gas to every single room connected to the system.
That’s the scenario that makes aircon relevant to carbon monoxide risk in Sydney homes. Not as a source — but as an unwitting distributor.
How Carbon Monoxide Gets Into Your HVAC System
There are several specific ways CO from other appliances ends up in your air conditioning or ducted heating system.
1. Shared Ductwork With a Gas Heater
The Most Common Pathway in Sydney Ducted Systems
Many Sydney homes — particularly those built in the 1980s and 1990s — have ducted systems that combine both cooling and gas heating through the same duct network. The air handling unit contains both the cooling coils and the gas heating element.
The heat exchanger is responsible for transferring heat from combustion gases to the air that circulates through your home. A crack in this component can allow carbon monoxide to escape into your indoor air supply.
When a heat exchanger develops even a hairline crack — which happens naturally as the metal expands and contracts through years of heating cycles — combustion gases including CO bypass the separation between the exhaust system and the circulating air. Every time the system runs, CO-contaminated air is distributed through every room.
2. Negative Air Pressure — The Backdraft Problem
How Your HVAC System Can Draw CO in From Outside
Open flue gas heaters are particularly sensitive to negative air pressure in the room environment.
In certain circumstances, exhaust fans and HVAC systems can draw carbon monoxide back into the room. Open flue heaters are not designed to operate in better-sealed, newer houses that may have less ventilation.
This is especially relevant in modern Sydney apartments and tightly sealed homes where energy efficiency upgrades have reduced natural air exchange. When the HVAC system creates negative pressure indoors, it can pull exhaust gases from open-flued gas heaters back into the living space rather than allowing them to vent safely outside.
3. Blocked or Damaged Flues
When CO Has Nowhere Safe to Go
If the flue pipe or exhaust system is blocked — due to debris, bird nests, or corrosion — carbon monoxide may be forced back into your home instead of venting outside.
In Sydney’s older suburbs — Parramatta, Bankstown, the Hills District, and across the Inner West — gas heaters with original flue systems can develop blockages from bird nesting, corrosion, or debris accumulation.
Once the flue is compromised, CO has nowhere to go except back into the room, where it gets picked up by the HVAC system’s return air intakes.
4. Unflued Gas Heaters — Sydney’s Most Common CO Risk
The Appliance Type That Poses the Highest Danger
There is a risk of accidental carbon monoxide poisoning from domestic gas heaters.
All gas heating appliances, and especially open-flued gas heaters, should be serviced and tested by an appropriately trained and licensed gasfitter at least every two years.
Unflued gas heaters — which vent combustion byproducts directly into the room rather than outside — are particularly dangerous when used in conjunction with ducted air conditioning. The CO they produce gets drawn into the return air vents and distributed throughout the home.
Carbon Monoxide Symptoms — What to Watch For in Your Sydney Home
This is the part that can save lives.
Early warning signs include a dull headache, general weakness, dizziness, and nausea or vomiting. As exposure continues, symptoms can worsen to include confusion, blurred vision, and eventual loss of consciousness.
CO Poisoning Symptoms — From Early to Severe
| Exposure Level | Symptoms |
| Mild (early stage) | Headache, fatigue, slight breathlessness, dizziness |
| Moderate | Severe headache, drowsiness, nausea, confusion |
| Severe | Vomiting, impaired vision, difficulty walking |
| Critical | Loss of consciousness, cardiac arrest, death |
The Key Difference From the Flu
CO poisoning is frequently mistaken for influenza or food poisoning — which is exactly what makes it so dangerous.
CO poisoning does not cause nasal congestion or fever. CO poisoning can also affect multiple people in the home or office at once, unlike the flu, which usually only affects one person.
If multiple people in your household develop headaches, nausea, or dizziness simultaneously — particularly in winter when gas heating is running — do not assume it’s a coincidence. Get everyone outside and call 000 immediately.
Who Is Most Vulnerable in Sydney Households
Children, pregnant women and their unborn babies, older people, and people with asthma or other chronic illnesses are at increased risk from air pollutants including carbon monoxide.
These groups can reach dangerous CO exposure levels at lower concentrations and in shorter timeframes than healthy adults.
Warning Signs Something Is Wrong With Your Gas Appliances
Beyond physical symptoms, your home itself gives you signals. Watch for:
Streaks of soot or black stains around your furnace or other fuel-burning appliances. A pilot light that repeatedly blows out or has a flickering yellow flame instead of a steady blue one.
Excessive, unexplained moisture or condensation forming on the inside of windows. A stuffy or stale feeling throughout the house even when the HVAC system is running.
Any one of these signs warrants an immediate inspection by a licensed gasfitter — before you run your heating again.
How to Protect Your Sydney Home From CO Risk
1. Install Carbon Monoxide Detectors
Your Single Most Important Safety Step
Install CO detectors strategically throughout your space.
Regularly check their functionality and replace batteries. Interconnect alarms to ensure swift detection.
Place CO alarms on every level of your home — particularly near sleeping areas and close to any gas appliances. In NSW, carbon monoxide detectors are not yet legally mandatory in residential properties, but they are strongly recommended by NSW Health and the NSW Fire Brigade.
Choose a model that meets Australian Standard AS 7240.16 or carries a recognised international certification — EU or US standard models are also acceptable according to Victorian health guidance.
2. Service All Gas Appliances Regularly
The Legal Requirement and Why It Matters
All types of gas heaters — including central heating units, space heaters, wall units, and gas log fires — should be serviced a minimum of every two years by a licensed gasfitter who has completed training on detecting and correcting risks of carbon monoxide spillage.
In NSW, gas appliance servicing must be carried out by a licensed gasfitter.
For older gas heaters — particularly open-flued models more than ten years old — annual servicing is strongly recommended rather than the minimum biennial schedule.
Before winter arrives each year, this should be the first thing on your home maintenance list.
3. Never Use Outdoor Gas Appliances Inside
Do not bring outdoor gas appliances inside — such as a patio heater. This is dangerous and could lead to carbon monoxide poisoning.
This applies equally to portable gas stoves, barbecues, and generators.
In enclosed or poorly ventilated Sydney homes, even brief indoor use of outdoor combustion appliances can build CO to dangerous levels within minutes.
4. Ensure Adequate Ventilation When Gas Is Running
Balancing Energy Efficiency With Safety
Sydney homes built or renovated for energy efficiency are increasingly airtight — which is excellent for power bills but creates real risks with open-flued gas appliances.
Open flue heaters are not designed to operate in better-sealed, newer houses that may have less ventilation. Testing should include the flue and checking for adequate ventilation in the house.
If you’ve added insulation, sealed gaps, or upgraded to double glazing in a home with an older open-flued gas heater, have a licensed gasfitter specifically assess whether your ventilation is adequate for safe heater operation.
5. Get Your Ducts Inspected
Sealing the Pathways CO Uses to Enter Your HVAC
If other appliances leak CO into attics or crawlspaces, damaged ductwork can suck the gas in and spread it through the vents. Have professionals seal any gaps or holes in your ductwork.
An annual HVAC inspection that includes ductwork integrity checking, heat exchanger assessment, and flue condition review is the most comprehensive protection available to Sydney homeowners who use gas heating within a ducted system.
If You Suspect CO Is in Your Home — Act Immediately
If you suspect you may be affected by carbon monoxide from a gas appliance, immediately turn it off and open the doors and windows to ventilate the area.
Emergency Steps
- Get everyone out of the building immediately — including pets
- Leave doors and windows open on your way out to begin ventilating
- Call 000 — tell the operator you suspect carbon monoxide poisoning
- Do not re-enter until emergency services declare it safe
- Do not turn any appliances back on until a licensed gasfitter has inspected and cleared the system
Frequently Asked Questions AC and Carbon Monoxide in Sydney
1. Can my split system air conditioner leak carbon monoxide?
No. Split system AC units run entirely on electricity and refrigerant — they produce zero carbon monoxide. The risk comes from gas appliances that share ductwork or space with your HVAC system.
2. How does carbon monoxide get into a ducted air conditioning system?
CO from a cracked gas heater heat exchanger, blocked flue, or open-flued heater can enter shared ductwork and get distributed by the AC blower fan through every connected room in the home.
3. What are the first signs of carbon monoxide poisoning at home?
Early symptoms include unexplained headaches, dizziness, fatigue, and nausea — particularly affecting multiple household members simultaneously. Symptoms improve when you leave the building and return indoors.
4. How often should gas heaters be serviced in Sydney to prevent CO risk?
Australian health authorities recommend a minimum of every two years by a licensed gasfitter — annually for heaters over ten years old or open-flued models in tightly sealed homes.
5. Where should I install CO detectors in my Sydney home?
Place CO alarms on every level of your home, near sleeping areas, and close to any gas appliances. Choose models meeting Australian Standard AS 7240.16 or recognised international equivalents.
6. What should I do if my CO detector goes off?
Get everyone — including pets — out of the building immediately. Leave doors and windows open as you exit. Call 000 from outside. Do not re-enter until emergency services clear the property.
Conclusion
Your air conditioner cannot produce carbon monoxide — but it can absolutely distribute it if another gas appliance in your home is leaking.
In Sydney homes where gas heating and ducted air conditioning share the same system, a cracked heat exchanger, blocked flue, or poorly ventilated open-flued heater creates a pathway for CO to enter every room in the house — silently, invisibly, and potentially fatally.
The protection is straightforward. Install CO detectors on every level of your home.
Have every gas appliance serviced by a licensed gasfitter at least every two years.
Never bring outdoor combustion appliances inside. And if multiple people in your household feel unwell simultaneously — get out and call 000.
Carbon monoxide doesn’t give you a warning. A detector does.
