Where to Put a Carbon Monoxide Alarm

Do you need one?

Carbon monoxide comes from fuel that doesn't burn properly: gas, oil, coal and wood. You can't see, smell or taste it, so an alarm is the only way to know it's there. Appliances that burn fuel can produce it: boilers, gas fires, log burners, open fires, oil heaters, even a barbecue.

Whether the law requires one depends on where you live and what you're doing:

• England, building work: Approved Document J says a carbon monoxide alarm should be fitted in the room whenever a new or replacement fixed boiler, fire or stove (gas, oil or solid fuel) is installed. Gas appliances used only for cooking are excluded.
• England, rented homes: GOV.UK's guidance says landlords must have one in every room used as living accommodation that has a fixed combustion appliance (not a gas cooker), and check it works on the first day of each tenancy. More on our landlord alarms page.
• Scotland, every home: owned or rented, the Scottish Government says you must have a carbon monoxide detector in the same room as a carbon-fuelled appliance such as a boiler, open fire or wood burner. Its guidance on the standard adds every room a flue passes through. Both apply to the rooms you live in, not attics, cellars or garages. Gas cookers and hobs don't need one.
• Wales, rented homes: the Welsh fitness for human habitation regulations require a working carbon monoxide alarm in each room with a gas appliance, an oil-fired appliance or a solid fuel appliance.

Elsewhere, and for older appliances, it may not be a legal duty. We'd fit one anyway in every room with a fuel-burning appliance: it's the only reliable warning. If you're not sure what applies to you, your council's building control can tell you.

Where to put it in the room

In England, Approved Document J puts the alarm in the same room as the appliance:

• on the ceiling, at least 300mm from any wall; or
• on a wall, as high as possible, above any doors and windows, but not within 150mm of the ceiling;
• and 1m to 3m horizontally from the appliance.

Government advice doesn't all say the same thing. GOV.UK's guidance for landlords says alarms should generally go "at head height, either on a wall or shelf", about 1m to 3m from the source. Both agree on the distance. Our advice: follow the instructions that come with your alarm, which GOV.UK and Gas Safe Register both say to do. Where the instructions don't say, use the building regulations position.

Wherever it goes, avoid:

• dead-air spots, such as corners and the peak of a sloping ceiling, where air doesn't circulate;
• being hidden behind curtains or furniture, if it's a free-standing alarm on a shelf or table;
• being too close: right next to the boiler or stove is nearer than the 1m the guidance asks for;
• cupboards: if the boiler is in a cupboard or another small enclosed space, put the alarm in the room outside it, still 1m to 3m away. Scotland's guidance says so, and it makes sense anywhere.

How many you need

One in every room with a fuel-burning appliance, and Gas Safe Register suggests more in the rooms where people sleep or spend a lot of time. In a typical house with the boiler in the kitchen and a log burner in the living room, that's an alarm in each of those rooms, and we'd add one in the main bedroom. Carbon monoxide alarms don't need to be linked to your smoke alarms.

Boilers, log burners, gas fires and cookers

• Boilers: in the room with the boiler. When a boiler is fitted or replaced in England, building regulations expect an alarm in that room, so ask the installer to include one. An alarm doesn't replace the yearly service: see boiler service costs.
• Log burners and open fires: in the same room. A new or replacement stove in England needs one under building regulations; see log burner costs.
• Gas fires and heaters: in the same room; a new or replacement gas fire needs one in England too.
• Gas cookers and hobs: not required in England or Scotland, though Gas Safe Register advises an alarm in every room with a gas appliance, and we'd fit one in the kitchen. In a rented home in Wales, the rule covers any gas appliance.
• Flues: in Scotland, any room a flue runs through needs one too.

Choosing an alarm

• Marked BS EN 50291, ideally with a BSI Kitemark or LPCB mark, which means it's been independently tested.
• A battery sealed in for the alarm's life, or a mains-wired one fitted by an electrician. Building regulations in England don't accept plug-in alarms for new installations, and Scotland requires sealed batteries.
• A proper alarm that sounds, not a "black spot" or colour-change card: Gas Safe Register warns those can't wake you up.

There are also alarms with vibrating pads and flashing lights for people who are deaf or have hearing loss.

Testing it, and when to replace it

Press the test button weekly or monthly, as the maker says, and keep dust off it with a dry cloth or a vacuum. The sensor wears out: they typically last 5 to 10 years, and the expiry date is printed on the side. A regular chirp near the end of that life is easy to mistake for a low battery, so check the date before you change anything.

An alarm is a last line of defence. The first is having your appliances serviced (a gas boiler once a year, by a Gas Safe registered engineer) and keeping air bricks, vents and the flue's outside grille clear.

If the alarm goes off

Frequently asked questions