Carbon monoxide safety
Carbon monoxide (CO) is produced by any fuel-burning appliance when combustion is incomplete. It has no smell, no colour, and no taste. Each year it kills hundreds of people in their own homes — most while asleep. A CO alarm and annual appliance servicing are the two things that prevent this.
The two-step prevention
Install a CO alarm in every room with a fuel-burning appliance. Have every fuel-burning appliance serviced annually by a Gas Safe (UK) or licensed (US) engineer. These two actions account for nearly all preventable CO deaths.
Poisoning symptoms
CO concentration and effects
Common sources
Appliances and situations that produce CO
What to do if your CO alarm sounds
A sounding CO alarm is an emergency — treat it as such, even if no one feels unwell. CO poisoning impairs judgement; people who feel "fine" have been found unconscious minutes later. The correct response is: get everyone out immediately, leave the door open, call the gas emergency line (UK: 0800 111 999) or 999 / 911 if anyone is symptomatic. Do not re-enter until a qualified engineer has inspected and cleared the building.
If anyone is unconscious or unresponsive:
- Call 999 (UK) or 911 (US) immediately
- Move them to fresh air if you can do so safely
- Begin CPR if they are not breathing and you are trained
- Do not re-enter the building to recover belongings
Annual servicing
CO is most commonly produced when a flue is blocked, corroded, or incorrectly installed — scenarios that develop gradually over years and are invisible to the occupant. Annual servicing by a qualified engineer checks the flue for obstructions and integrity, combustion efficiency, and gas pressure. In the UK, engineers must be on the Gas Safe Register. In the US, look for an engineer with a relevant NFPA-qualified certification or your state licensing equivalent.
For the full heating season safety checklist — including CO alarm replacement intervals — see our heating season checklist. For space heater safety specifically, see space heaters without the risk.
Sources: US CPSC · NHS · Gas Safe Register · NFPA 72
Carbon monoxide FAQ
Questions about CO safety and alarms
Carbon monoxide (CO) is completely odourless and colourless — you cannot smell, see, or taste it. This is what makes it so dangerous. The only reliable way to detect CO in your home is with a functioning CO alarm. Symptoms of CO poisoning (headache, nausea, dizziness, confusion) can be mistaken for flu or food poisoning. If multiple people or pets in the same building feel unwell at the same time, CO poisoning should be considered. See the US CPSC CO safety centre and NHS carbon monoxide poisoning guidance.
Any fuel-burning appliance can produce CO if it malfunctions or is poorly ventilated. This includes: gas boilers, gas fires, log burners and open fires, wood pellet stoves, oil-fired boilers, paraffin heaters, petrol or diesel generators, gas hobs, and portable gas camping stoves. Electric appliances do not produce CO. The most common sources of dangerous CO levels in homes are faulty or blocked boiler flues, poorly installed gas appliances, and using fuel-burning heating in rooms without adequate ventilation.
Install a CO alarm in every room that contains a fuel-burning appliance, and on every sleeping level. CO is slightly lighter than air and distributes fairly evenly, so wall mounting at head height (1–1.5 m / 3–5 ft) or ceiling mounting is both acceptable. Do not position alarms directly above or adjacent to cooking appliances (false alarms from cooking gas). The NFPA 72 standard specifies CO alarm placement requirements for new residential construction in the US.
Act immediately: (1) Get everyone — including pets — out of the building. (2) Leave the door open on your way out to ventilate. (3) Call the gas emergency number (0800 111 999 in the UK; your gas supplier in the US) or 999 / 911 if anyone is unwell. (4) Do not re-enter until the building has been inspected by a qualified engineer. Do not silence the alarm and go back to sleep. Even if you feel fine, CO poisoning can cause loss of consciousness without warning at higher concentrations.
CO alarms have a finite lifespan — typically 7–10 years — because the electrochemical sensor degrades over time. The manufacture date is printed on the back of the unit. Replace CO alarms before the expiry date even if they still appear to function. The test button on a CO alarm checks the alarm circuit and sounder, not the sensor — an alarm can pass the test while its sensor is no longer sensitive to CO. Check the date on every CO alarm in your home today. Also see our heating season checklist for annual alarm checks.