Where to fit a carbon monoxide alarm
Updated: 20 October 2026
The boiler is on the kitchen wall, the alarm is still in the box, and two official sentences point at different heights. One is a ceiling rule. The other says head height. Where to fit a carbon monoxide alarm is the ceiling or a high wall in the same room as the appliance, at the distances in Approved Document J, then a button test you can repeat without gas. The [CO detector comparison](/hub/fire-protection/co-detector) lines the sealed models up. This page is the fitting, the test, and four chirps against one. A unit in a cupboard never hears the room.
The boiler is on the kitchen wall, the alarm is still in the box, and two official sentences point at different heights. One is a ceiling rule. The other says head height.
The boiler is on the kitchen wall, the alarm is still in the box, and two official sentences point at different heights. One is a ceiling rule. The other says head height. Where to fit a carbon monoxide alarm is the ceiling or a high wall in the same room as the appliance, at the distances in Approved Document J, then a button test you can repeat without gas. The CO detector comparison lines the sealed models up. This page is the fitting, the test, and four chirps against one. A unit in a cupboard never hears the room.
Our top picks
| Badge | Product | Battery | Alarm pattern | One chirp | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Kidde Kidde 5CO | AA, life not stated | Not stated as four chirps | Pattern not stated | 6.3 | about £13.75 | View offer |
| Best value |  FireAngel FireAngel FA6813 | 2 × AA | Four chirps, red CO light | Sleep Easy, 8 hours | 8.7 | about £13.98 | View offer |
 FireAngel FireAngel FA3820 | Sealed 10 years | Four beeps | Replace the whole unit | 9.4 | about £22 | View offer |
On this page
Same room, then ceiling or high wall
Fit the alarm in the same room as the fuel-burning appliance, on the ceiling or high on a wall. Approved Document J, in the circular that took effect on 1 October 2022, sets that spot for a fixed solid-fuel, gas or oil appliance in England. A cooker is outside that sentence. Scotland's Chapter 17 uses the same ceiling and wall gaps, and note 4 adds the same 1 m to 3 m range.
On the ceiling, stay at least 300 mm from any wall. On a wall, stay at least 150 mm below the ceiling, above doors and windows. A combi screwed behind its casing is the usual miss: closer than 1 m, in still air, it never samples the room. The landlord booklet, which never names a height, is a different sentence.
Head height is a different sentence
England's landlord regulations do not stipulate where the alarm goes. The GOV.UK booklet says so, then offers head height, about 1 m to 3 m from the floor, as general advice. That tip is not the Approved Document J sentence. If you treat them as one height, the alarm ends up at eye level, inside the 150 mm gap or well below it.
Follow the ceiling or high-wall distances when a fixed appliance is installed or replaced. Use the booklet only when you are not working to that specification. Who must supply the alarm, including beside a gas hob, is on the carbon monoxide alarm landlord rules page.
Four chirps, or one
Four loud chirps mean you treat the air as carbon monoxide until you know otherwise. On the FireAngel FA6813 that pattern comes with a red CO light. On the FA3820, four continuous beeps are the alarm in that brand's guide. That legend is FireAngel's, not every brand's. If anyone has a headache, dizziness, nausea or confusion, leave before you count the beeps.
A single regular chirp is not that alarm. On a sealed FA3820 it means low battery, a fault or end of life, and you replace the whole unit because there is no cell to change. On the FA6813, Sleep Easy mutes the low-battery chirp for eight hours, up to ten times, while the amber light keeps flashing. It does not mute a carbon monoxide alarm.
If it is carbon monoxide
Get everyone out, and do not go back for a charger or to silence the noise. Stop the appliance if the switch is on the way. Call 999 if someone is drowsy, confused or struggling to breathe. For a milder headache, dizziness or nausea, seek NHS advice from outside.
FireAngel prints 0800 111 999 for the National Gas Emergency Service. A solid-fuel stove is not the same call: leave, get help if anyone is ill, and keep the stove off until a competent person has checked it. A gas boiler needs a Gas Safe registered engineer. This set has no mains unit, and fixed mains wiring needs a qualified electrician.
Common questions
Does the alarm go on the ceiling or at head height?
For a fixed solid-fuel, gas or oil appliance, Approved Document J puts the alarm on the ceiling at least 300 mm from a wall, or high on a wall at least 150 mm below the ceiling, in the same room. The England landlord booklet does not set a position. Its head-height tip, about 1 m to 3 m, is separate general advice.
How far from the boiler should I fit it?
Place the alarm 1 m to 3 m horizontally from the appliance, in the same room. Approved Document J and Scottish Chapter 17 both use that range, together with the ceiling and wall gaps. Inside 1 m the unit can sit in still air beside the casing. Beyond 3 m it can miss the air the boiler is heating. Measure to the appliance, not the door.
Can I put it next to a gas hob?
Keep the detector away from a gas hob. Scottish guidance warns that cooking fumes cause false alarms, and Scotland does not require an alarm for a cooker alone. Wales does ask for an alarm in a rented room with a gas hob, with the spot still taken from the manufacturer.
How do I test it without carbon monoxide gas?
Press the test button. It checks the sounder and the circuit, not whether the sensor still meets BS EN 50291. Devon and Somerset Fire and Rescue say at least monthly. Surrey County Council says weekly. Use the manual's interval when it gives one. A FireAngel FA3820 test is two loud sequences of four beeps. Do not use hob gas as a substitute.
What does one chirp mean, and can I mute it overnight?
One regular chirp points to low battery, a fault or end of life, as your manual defines the pattern. A sealed FireAngel FA3820 has no cell to swap, so you replace the unit. On the FA6813, Sleep Easy mutes that low-battery chirp for eight hours, up to ten times, and the amber light keeps flashing. It does not silence a carbon monoxide alarm. Do not pull a battery to stop four chirps.
Related pages
Sources
Public UK sources and the FireAngel FAQ, last checked on 19 October 2026.
- The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, regulation 4 (retrieved 19 October 2026)
- GOV.UK smoke and carbon monoxide alarm Q&A for landlords (retrieved 19 October 2026)
- Approved Document J divisional circular on alarm amendments (retrieved 19 October 2026)
- Scottish Government tolerable standard, fire and carbon monoxide detection (retrieved 19 October 2026)
- mygov.scot home fire safety (retrieved 19 October 2026)
- Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022, regulation 5 (retrieved 19 October 2026)
- NHS carbon monoxide poisoning (retrieved 19 October 2026)
- FireAngel homeowner FAQs (retrieved 19 October 2026)