What is Carbon Monoxide (CO)?
08/12/2025
There are many joys of an open fire or stove — warmth, comfort, and that relaxing glow on a winter evening. But any fuel-burning appliance (wood, smokeless fuel, coal, pellets, gas or oil) can produce carbon monoxide (CO) if it isn’t burning or venting properly.
Carbon monoxide is especially dangerous because you can’t see it, smell it, or taste it. The good news is that simple steps — servicing, chimney/flue maintenance, ventilation and fitting a certified CO alarm — dramatically reduce the risk.
Carbon Monoxide (CO): at a glance
What it is: a poisonous gas created when fuels burn incompletely.
Common symptoms: headache, dizziness, nausea, tiredness, confusion and breathlessness (often “flu-like”, usually without a fever).
Clue it might be CO: symptoms improve outdoors and return indoors, especially when heating is on.
Best protection: regular servicing + swept chimney/flue + good ventilation + a certified CO alarm.
What is carbon monoxide (CO)?
Carbon monoxide is a gas produced when carbon-based fuels (such as wood, smokeless fuel, coal, pellets, gas or oil) do not burn fully. If CO builds up indoors, it can make you seriously unwell very quickly.
What is carbon monoxide poisoning?
Carbon monoxide poisoning happens when you breathe in CO and it enters your bloodstream. CO binds to haemoglobin (the part of your blood that carries oxygen), which means less oxygen is transported around your body. That reduction in oxygen is what causes the symptoms — and why severe exposure can be life-threatening.
What causes carbon monoxide to build up?
In a well-maintained, correctly installed appliance with a clear chimney/flue and the right ventilation, fumes should vent safely outside. Problems usually arise when one or more of the following apply:
Blocked or restricted chimney/flue (soot build-up, birds’ nests, debris, damaged liners)
Poor ventilation (airbricks blocked, vents closed, sealed rooms without adequate air supply)
Faulty, poorly installed or poorly maintained appliance
Back-draughts caused by competing airflow (kitchen/bathroom extractor fans, tumble dryers)
Carbon monoxide poisoning symptoms (CO symptoms)
CO symptoms can be subtle at first and are commonly mistaken for a cold or flu (often without a temperature). Look out for:
- Headache
- Dizziness or light-headedness
- Feeling sick (nausea) or being sick
- Weakness or unusual tiredness
- Confusion or difficulty concentrating
- Shortness of breath
- Chest pain (particularly concerning if you have heart problems)
- Higher exposure can cause loss of coordination, collapse, loss of consciousness and can be fatal.
How to tell if it might be carbon monoxide
CO is more likely if:
Symptoms improve when you go outside and return when you’re back indoors
Symptoms worsen when the heating or fire is on
More than one person in the home feels unwell at the same time
Pets seem unusually lethargic or unwell
If you suspect CO, don’t “wait and see”.
Posted in: Firewood
