If you've just bought a carbon monoxide alarm and you're standing in the hallway wondering where it goes, here's the short version.
Put a carbon monoxide detector on a wall, roughly at head height (about 1.5m off the floor), between one and three metres horizontally from the appliance that could produce CO — a boiler, gas fire, wood burner or cooker. Not on the ceiling like a smoke alarm, and never tucked behind a curtain, inside a cupboard or right next to the flue.
That one paragraph puts you ahead of half the installs we see cross the trade counter on Villa Road. But height is only half the story — which room, and how many, is where people go wrong. So let's do this properly.
1. Why CO alarms sit on the wall, not the ceiling
Smoke rises, so smoke alarms live on the ceiling. Carbon monoxide doesn't behave that way. It's almost exactly the same density as air, so it mixes and spreads evenly through a room rather than pooling at the top. That's the whole reason the siting rules are different.
The practical read: mount the alarm at breathing height for someone sitting or sleeping — around 1.5m from the floor is the sweet spot. High enough to be out of the way, low enough to represent the air you're actually breathing. If your only realistic option is the ceiling (some rooms just don't have a good wall), it can go there, but keep it at least 300mm away from any wall and away from the light fitting.
Trade Tip: The number one mistake we see every week is people treating a CO alarm like a smoke alarm and sticking it dead-centre on the ceiling above the boiler. It'll still work — but you've picked the least representative spot in the room. Wall, head height, a metre or two to the side. Every time.
2. The distance-from-appliance rule
Too close and you'll get nuisance alarms from the brief, harmless CO puff some appliances give on start-up. Too far and you're slow to detect a genuine leak. The trade-standard window is between 1 and 3 metres horizontally from the appliance.
If the alarm has to share a wall with the boiler, keep it off to one side rather than directly above the flue. And if a room is long — an open-plan kitchen-diner, say — measure from the appliance, not from the middle of the room.
For the room with the boiler or a mains supply nearby, the Aico Ei3018 Carbon Monoxide Alarm is the one landlords keep coming back for. It's a mains-powered, electrochemical-sensor CO alarm that's Ei3000MRF compatible — meaning it can be linked into a wider Aico system so that if one alarm triggers, the others can too. Wall-mount it at head height, keep it in the 1–3m window, and it does exactly one job well.
3. Which rooms actually need one
Prioritise, in this order:
Any room with a fuel-burning appliance — boiler, gas hob, gas or wood fire, a back boiler. That's non-negotiable. Then bedrooms or a room used as sleeping accommodation, because CO poisoning while asleep is the deadliest scenario — you never wake up. Then rooms a flue passes through, even if the appliance itself is elsewhere.
A kitchen with a gas hob counts, but site the alarm away from the immediate cooking zone and steam to avoid nuisance triggers — the far wall, still within a few metres.
For bedrooms and rooms without a handy mains point, the Aico Ei208 Battery Carbon Monoxide Alarm is the sensible pick — a 10-year lithium cell, sealed in, with AudioLINK+ so it can report its status. No wiring, no annual battery hunt for a decade. Screw it to the wall at head height and forget about it until it tells you otherwise.
4. The spots to avoid completely
A CO alarm is only as good as the air reaching it. Keep it out of:
Cupboards and enclosed spaces. Behind curtains or furniture. Directly above a sink or the cooker. Within 300mm of a door or window (draughts skew the reading). In an unheated space that regularly drops below the alarm's operating temperature — a bare garage in January, for instance. And not immediately next to the flue or in the path of the appliance's direct exhaust.
Trade Tip: Damp and dust kill sensors early. Don't mount a CO alarm in a steamy en-suite or a dusty utility corner and expect ten clean years out of it. Clean air, stable temperature, head height — that's the recipe for it lasting its full sensor life.
5. One alarm or a linked system?
A single standalone alarm protects the room it's in. Fine for a one-appliance flat. But in a house with a boiler downstairs and bedrooms upstairs, a CO leak at the boiler might sound an alarm nobody can hear from bed. This is where the money either gets spent well or wasted.
The Aico Ei208WRF RadioLINK+ Carbon Monoxide Alarm solves that without chasing wires across the house. It's a battery-powered CO alarm with RadioLINK+ wireless interconnect — link it to your other Aico alarms and a trigger in the kitchen sounds every unit in the property, including the one by the bed. For retrofits, where running interconnect cable would mean lifting floors, wireless linking is the honest answer, every time.
Browse the full range of carbon monoxide alarms and, if you're covering smoke as well, our fire and safety alarms — just remember a combined smoke/CO unit follows the ceiling-mounting rules of a smoke alarm, not the wall-height CO rule above.
6. Summary table
| Question | The trade answer |
|---|---|
| Height | ~1.5m off the floor, on a wall (head height) |
| Ceiling? | Only if no wall option; keep 300mm from walls/fittings |
| Distance from appliance | 1–3m horizontally, off to the side of the flue |
| Priority rooms | Any with a fuel-burning appliance, then bedrooms |
| Avoid | Cupboards, behind curtains, above sink/cooker, near doors/windows, cold garages |
| Whole-house cover | Interlinked alarms (wired or RadioLINK+ wireless) |
7. Expert Help in the West Midlands
We're WME — West Midlands Electrics, trading from Villa Road in Birmingham since 1975. If you're not sure which CO alarm suits your property, or whether to go battery or mains, bring the details to the trade counter and we'll talk it through with you over the actual boxes. We stock Aico, Ajax and more, and we'd rather send you home with the right one than the dearest one. No appointment, no upsell — just people who fit these for a living.
Frequently asked questions
How high should a carbon monoxide detector be placed?
About 1.5m from the floor — head height on a wall. Unlike smoke alarms, CO alarms don't go on the ceiling, because carbon monoxide mixes evenly through the air rather than rising.
Can I put a carbon monoxide alarm next to the boiler?
On the same wall is fine, but keep it 1–3m to the side rather than directly above the flue. Too close and you may get nuisance alarms on start-up; too far and detection is slower.
Do I need a carbon monoxide alarm in every room?
Not every room — prioritise any room with a fuel-burning appliance and any bedroom. In a multi-storey home, interlinking the alarms means a leak downstairs still wakes you upstairs.
Carbon monoxide is a genuine safety issue. This guide is general good practice; always follow the alarm manufacturer's instructions and current UK guidance, and use a Gas Safe registered engineer for anything to do with the appliance itself.