Smoke & CO Alarm Placement: A UK Homeowner's Room-by-Room Guide
Where to put smoke and CO alarms in a UK home to actually save lives — not just tick a box. NICEIC-led guide with current regulations.
Most homes I inspect have alarms in the wrong places or too few of them. A £15 CO alarm on the wrong wall is worse than no alarm — it gives false comfort. Here's how to get it right room by room.
Smoke alarms — where and how many
Under British Standard BS 5839-6 (the domestic standard) the current best-practice Grade D1 setup for a two-storey UK home is:
- One smoke alarm on the ceiling of every hallway and landing.
- One smoke alarm in the living room (main sitting/TV room).
- One heat alarm (not smoke) in the kitchen.
- Interlinked so they all sound together — mains-powered with sealed 10-year battery back-up.
Optional but recommended: one in each bedroom, especially where anyone charges devices overnight.
CO alarm placement — the bit most people get wrong
Carbon monoxide is roughly the same density as air, not lighter — so mounting at ceiling height like smoke alarms is fine but not required. Manufacturers now specify a zone: 1–3m horizontally from the appliance, at least 150mm from any wall/ceiling junction, and NEVER inside an enclosed cupboard containing the boiler.
Fit a CO alarm in every room with a fuel-burning appliance:
- Room with a gas boiler.
- Room with a gas hob (if used heavily).
- Room with a wood-burner, open fire or flued gas fire.
- Any room where a flue passes through.
- Bedrooms where anyone sleeps with a fuel-burning appliance in the room.
Homeowners aren't legally bound but Building Regulations Approved Document J applies to any new fuel-burning appliance you install.
Where NOT to put them
- Inside a bathroom or en-suite (steam causes false alarms).
- Directly above a hob (grease and steam kill sensors in 6 months).
- Within 300mm of a light fitting or ceiling rose.
- Inside the airing cupboard containing the boiler.
- Behind furniture or curtains where airflow is restricted.
Test schedule that actually works
- Weekly: press the test button on one alarm (rotate through the house).
- Monthly: vacuum around the alarm cover to clear dust.
- Annually: replace batteries in older alarms (10-year sealed units don't need this).
- Every 10 years: replace the entire alarm — sensors degrade.
Interlinking — worth the small extra cost
An interlinked system (RF or mains-linked) sounds every alarm when any one detects. In a two-storey home, this is the difference between the family waking up and not. Aico, FireAngel and Kidde all offer wireless kits for under £120 for a 3-alarm set.
Cover and support
Our home emergency cover includes 24/7 access to a Gas Safe engineer if your CO alarm ever triggers — turn the appliance off, ventilate, call, and we get someone out within hours. Details on the pricing page.
FAQ
Do I need a CO alarm if my boiler is in an outhouse?
Yes — fit one in the outhouse itself, plus one in any room where the flue passes through.
Are combined smoke/CO alarms any good?
They meet the minimum standard but the two technologies really do belong in different rooms. Separate units are more reliable.
Summary
- One smoke alarm per storey, one CO alarm per fuel-burning appliance room.
- Interlinked mains alarms with 10-year sealed back-up are the modern standard.
- Test weekly, replace every 10 years — sensors don't last forever.