CO Alarm Distance from Boiler: Placement Rules for Landlords

Getting the right distance between a CO alarm and a combustion appliance matters more than most landlords realise. Too close and you risk nuisance activations; too far and the sensor responds too slowly to protect sleeping tenants. The statutory regulations don't prescribe an exact distance in centimetres, but official guidance and BS EN 50292 establish clear parameters.

The 1-to-3-Metre Rule

Government guidance recommends positioning a CO alarm at head height, on a wall or shelf, approximately 1 to 3 metres from the fixed combustion appliance. The regulations do not prescribe an exact mounting position, so also follow the alarm manufacturer's instructions. This positioning applies to gas boilers, oil-fired boilers, wood-burning stoves, solid-fuel fires, and pellet stoves alike.

For a standard combi boiler mounted on a kitchen or utility wall, that typically means the CO alarm sits at head height on a nearby wall or shelf, within the recommended distance and easy earshot of the main living space.

Enclosed Boiler Cupboards

Many rental properties house gas boilers inside small cupboards or plant enclosures. In this layout, fit the CO alarm outside the cupboard, within 1 to 3 metres of the appliance, at head height on a wall or shelf, and ensure the sounder is audible throughout the habitable room. Placing an alarm inside a sealed cupboard can muffle the sounder and delay occupants from hearing it.

If the cupboard door has no ventilation slots, consider an alarm at head height on the room-side wall just outside the cupboard door.

Room-Specific Scenarios

Open-plan living areas. In a studio or open-plan kitchen-living space with a boiler, one CO alarm positioned centrally near the appliance satisfies the statutory minimum, provided it's audible across the whole space. The smoke alarm for that storey can be the same unit (combined smoke/CO detectors exist) but each function must meet its respective British Standard — BS EN 14604 for smoke detection, BS EN 50291-1 for CO detection.

Wood-burning stoves and solid-fuel fires. These produce more particulate matter and heat variation. Position the CO alarm at head height, approximately 1 to 3 metres from the stove. If the stove is in a large room, err toward the closer end of the range.

Oil-fired boilers. Same 1-to-3-metre rule applies. Oil boilers in outbuildings or detached plant rooms present a complication — the CO alarm must be in the room containing the appliance, and that room needs to qualify as "living accommodation" for the statutory duty to apply. A detached boiler house that tenants never enter may fall outside the regulation (though fitting a CO alarm there is good practice regardless).

Concealed flues. Where boiler flues pass through ceiling voids or adjoining rooms, prioritise detection in the room containing the main appliance body. Flue leaks are less common than appliance-level failures, but if you suspect flue routing through a habitable room, a second CO alarm in that room adds meaningful protection.

Sleeping Areas

If a combustion appliance sits in or adjacent to a bedroom (common in older terraced houses with back-boiler systems), mount the CO alarm at head height on a wall or shelf, still within the 1-to-3-metre range of the appliance, and ensure the alarm can be heard at the bed. For tenants who are deaf or hard of hearing, consider specialist alarms that alert by vibration or flashing light; landlords must consider their Equality Act 2010 duties, and these alarms may be required.

What the Law Actually Requires

For premises covered by the Smoke and Carbon Monoxide Alarm (England) Regulations 2015 (as amended 2022), a CO alarm is required in any room used as living accommodation that contains a fixed combustion appliance — with rooms where the only such appliance is a gas cooker exempt. Premises for which a licence is required under Part 2 or Part 3 of the Housing Act 2004 are excluded and follow their licence conditions. The regulations don't specify exact mounting distances; government guidance recommends an alarm at head height, approximately 1 to 3 metres from the potential source. Follow the alarm manufacturer's instructions as well.

The complete compliance guide includes a storey-by-appliance mapping worksheet to document exactly where each alarm sits and why, which becomes your evidence trail if the council ever queries your setup.

See more England guides →