Why carbon monoxide needs an alarm, which alarm to fit, where Approved Document J places it, and how to keep it working.
You cannot see, smell or taste carbon monoxide. Those senses will not warn of exposure, and even relatively low levels can cause harm over time. Headaches, dizziness, nausea, breathlessness and tiredness that ease away from the property are the recognised pattern. That is why working appliances, good flueing and a CO alarm all matter.
Which alarm
Fit an alarm designed for the purpose that meets BS EN 50291-1, not a cheap or unbranded device. Under Approved Document J it runs on a battery designed to last its working life, with a warning when that life is due to end, or it is a fixed-wired mains Type A alarm with a sensor-failure warning. Plug-in alarms are excluded.
Where it goes
Follow the alarm manufacturer's instructions and the current guidance. For the room containing the appliance, Approved Document J places the alarm in the same room, between 1 m and 3 m from the appliance horizontally, and high up:
- on a ceiling: at least 300 mm from any wall; or
- on a wall: as high as possible, above any doors and windows, but not within 150 mm of the ceiling.
Keep it out of positions that distort its reading, such as right next to a flue, in the dead air where wall meets ceiling, or where it is obstructed.
Keep it working
An alarm is a back-up, not a fix. It does not make an appliance safe or replace adequate ventilation, a sound flue, correct combustion or routine servicing. Test it regularly and replace it at the end of its stated life: an alarm past its life or with a flat cell gives false reassurance. The test button checks the alarm, not the appliance.