Where to Install CO Detectors | Smoke Alarm Guide

Where to Install Carbon Monoxide Detectors: Placement Guide

Research and editorial review: Smoke Alarm Guide • Standards Context: Manufacturer Manuals & Fire Safety Guidelines • Updated: October 2026

Direct Answer

Install carbon monoxide detectors on every level of the home that contains fuel-burning appliances, inside or directly outside every sleeping area, and near attached garages. Because carbon monoxide mixes evenly with room air, detectors can be mounted at ceiling height, eye level, or outlet height.

NFPA 72 Spatial Clearance & Layout Rules

CO Placement Standards:
• Sleeping Areas: Place in hallways within 10 to 15 ft of all bedroom doors so alarms awaken sleepers.
• Every Living Level: Install at least one detector on each floor containing fuel-burning equipment.
• Distance from Fuel Appliances: Maintain at least 15 feet (4.5 m) separation from fuel appliances to prevent startup false readings.
• Mounting Height: Ceiling or wall (eye-level display models allow easy viewing of digital PPM readouts).

Illustration of home showing proper carbon monoxide detector placement outside bedrooms and near fuel appliances

Install CO alarms outside all sleeping areas, on every fuel-burning level, and at least 15 ft from fuel-burning appliances.

Pre-Installation Assessment Checklist

Identify all fuel-burning appliances (gas furnace, boiler, water heater, gas stove, fireplace, wood stove, attached garage).
Check local statutory requirements (many jurisdictions mandate CO alarms outside all bedrooms).
Ensure detectors are placed where alarm sounders are not muffled by heavy curtains or closed doors.

Carbon monoxide has a molar mass of 28.01 g/mol, which is virtually identical to ambient air (28.97 g/mol). Consequently, CO gas diffuses evenly throughout the entire room volume without stratifying at the floor or ceiling.

Fuel-Burning Appliance Clearances

Keep CO alarms at least 15 feet from fuel-burning appliances (furnace, boiler, water heater, fireplace, etc.), or follow the manufacturer's installation instructions. Avoid placing alarms in dead-air spaces, directly above appliances, or in the path of strong air currents from supply vents.

Room-by-Room Placement Guidelines

Home Location	Requirement Level	Recommended Placement
Sleeping Hallways	Mandatory	Centrally placed within 10 to 15 ft of all bedroom doors
Inside Bedrooms	Recommended	Particularly important if bedrooms contain fuel heaters or fireplaces
Furnace / Boiler Rooms	Mandatory	Place at least 15 feet away from fuel-burning heating appliances
Attached Garage Entry	Mandatory	Inside the home near the garage connecting doorway
Every Finished Floor	Mandatory	At least one detector per habitable level

Dead-Air Spaces & Placement Hazards to Avoid

Do not mount CO alarms directly inside dead air pockets behind furniture or in corners.
Do not mount detectors within 15 feet of fuel-burning appliances (normal startup produces brief harmless gas spikes).
Do not mount detectors directly above stoves or inside high-humidity shower rooms.

Important Safety Guideline

If your home has fuel-burning appliances or an attached garage, installing carbon monoxide detectors outside sleeping areas is required by law in most jurisdictions.

Combination Units on Ceilings

If installing a combination smoke/CO alarm, always follow smoke alarm placement rules (ceiling mount or top 12 inches of wall) to detect rising smoke.

SAG

Smoke Alarm Guide Editorial Team

Technical Standards Review

Researched from verified statutory standards, public safety publications, and official manufacturer manuals. Review our complete research methodology and primary source hierarchy.