Positioning and maintaining your carbon monoxide alarm
Carbon monoxide (CO) alarms are the most effective way to detect carbon monoxide in the air and alert you to the presence of the dangerous gas.
Carbon monoxide consists of one part oxygen and one part carbon and is produced by partially burned carbon fuel sources like natural gas, coal, petrol, wood and propane. While harmless in an outdoor or well ventilated area, carbon monoxide can be lethal in enclosed spaces. It is very difficult to detect because of its lack of odour and excess carbon monoxide starves the body of oxygen by combining with haemoglobin in the lungs. This can causes headaches, dizziness and nausea, before ultimately becoming fatal.
You can find out more about carbon monoxide on our ‘What is Carbon Monoxide Page?’.
Where to place a carbon monoxide detector
In order for your carbon monoxide alarm to work correctly, it is essential you put it in the right place. Here are the things you need to consider when placing a carbon monoxide detector:
- You should ideally have a carbon monoxide detector on each floor of your house and definitely in the same room as any fuel-burning appliance, such as a boiler, stove or oven.
- Place the alarm at head height. This could be on a shelf or bookcase; it doesn’t have to be fixed on a wall. Ideally, it should be
- At least 300 mm from any wall (for ceiling mounted alarms)
- At least 150 mm from the ceiling, above the height of any door or openable window (for wall mounted alarms)
- Make sure the alarm is between 1 and 3 m (measured horizontally) from the potential source of CO, such as boilers and ovens.
- Some carbon monoxide alarms are built into ceiling-mounted multipurpose fire alarms. You should check your smoke detector to see whether it is already fitted with a carbon monoxide detector. If the alarm is located on the ceiling, it should be at least 300 mm from any wall and any ceiling obstruction e.g. light fittings.
CO alarms must not
- Too near your fireplace or any appliance that produces flames (like your gas hob).
- In an enclosed space such as behind furniture or in a cupboard
- Where it can be obstructed.
- Directly above a sink.
- Next to an external door, window or ventilation equipment such as extractor fans, air vents or similar ventilation opening.
- Where the temperature may drop below –5 ºC or exceed 40 ºC (this can vary by manufacturer, please check the user manual).
Carbon monoxide alarm maintenance
You should think of the maintenance of your carbon monoxide alarm in the same terms as your smoke alarm. This means that it’ll require regular checks to ensure that it’s in working order, these should include:
- Test the ‘beep’ on the alarm at least once a week. You could set a reminder on your phone to remind you.
- Ensure batteries are changed, if necessary, at least once a year, and that you test the function immediately after changing.
- Pay attention to any ‘chirps’ from your alarm. These could be a warning of low batteries.
- Pay close attention to the alarm’s battery life and when it will need replacing. Most alarms will last between five and seven years, with some lasting for as long as 10 years.
Always read and follow the manufacturer’s instructions when placing, testing, and servicing the alarm.
How many carbon monoxide detectors should I have?
This depends on the size of your home. We recommend you have a carbon monoxide detector on every level of your home. These should be in rooms with fuel‑burning appliances as well as outside bedrooms. This includes basements and the garages.
Which carbon monoxide alarm should I buy?
Carbon monoxide alarms work like smoke or fire alarms, going off as soon as they detect surplus carbon monoxide in the air. There are three kinds of carbon monoxide detectors, all of which work slightly differently:
The alarm is set off by a colour-changing gel, which changes when it absorbs a certain level of carbon monoxide and triggers the warning.
Metal oxide semiconductor
Carbon monoxide reduces the electrical resistance in an electronic circuit, which trips the alarm and sets it off.
Changes in electrical currents, caused by the presence of carbon monoxide, in a chemical solution are detected by submerged electrodes. This then triggers the alarm.
Four tips for deciding which carbon monoxide alarm to buy
You should look out for several things when buying a carbon monoxide detector, ensuring you get the best product to help guarantee safety. Here are four things to remember:
- Buy a recognised brand - a carbon monoxide alarm is a potentially lifesaving piece of equipment – so it’s important that you buy a trusted brand. Any unbranded products or those from brands you’ve never heard of before should be approached with extreme caution.
- Ensure you buy an audible alarm - audible alarms are those designed to make a noise when carbon monoxide is detected and are therefore a much better option. Others, such as patch test alarms, are designed to change colour in the presence of carbon monoxide but require constant checking.
- Don’t look for a bargain - if it comes down to a choice between a slightly more expensive alarm and something cheaper (particularly anything under £10), be aware that this could impact the quality of the product. A carbon monoxide alarm is an important purchase, so it’s not the time to look for a bargain.
- Consider portable carbon monoxide alarms - people often assume that a carbon monoxide alarm must be hard-wired into the electrics of your home, however, this isn’t the case. Battery-powered, portable alarms are a great option and can be placed anywhere around the home or packed in your suitcase before going on holiday.
Before purchasing an alarm ALWAYS ensure it complies with a British Standard:
- Kitemarked to BS EN50291-1 (domestic use)
- Kitemarked to BS EN50291-2 (camping/caravans/boats)
Where to buy a carbon monoxide alarm
Buying a carbon monoxide alarm from a recognised high street retailer is one of the safest options when making a purchase. Carbon monoxide alarms are available from most DIY and hardware stores, as well as major supermarkets. Purchasing from one of these retailers should help to guarantee that you’re buying a quality product.
If you’re purchasing online, the same applies. Ensure you’re purchasing from a recognised and trusted seller.
What to do if your carbon monoxide alarm goes off
The first thing to do if your carbon monoxide alarm goes off is to try to improve the ventilation to the room, by opening all windows and doors to try and rid your house of the gas. Carbon monoxide is most dangerous and concentrated in a sealed-off environment, so you need to ventilate your home to give the gas somewhere to escape to.
You should turn off any fuel-burning appliances like fires, boilers, cookers or ovens as quickly and safely as possible, and immediately exit the building. You should then remain outside, regardless of whether you are suffering from any of the aforementioned symptoms.
Read our ‘Suspect Carbon Monoxide: What is Carbon Monoxide Poisoning?’ page for more information.
If you suspect that you may have a carbon monoxide leak in your property, call us immediately on 0800 111 999*
Please only call the national gas emergency number 0800 111 999 if you have a gas emergency: if you smell gas or you suspect you have a carbon monoxide issue. If you have an issue with your gas boiler or any other gas appliance, please see this advice.
If you live in a rented property
Private landlords in England are bound by law to fit carbon monoxide alarms where necessary, and failure to do so can lead to a fine of up to £5,000. You can find out more about the government guidelines for landlords here (opens in new window).