How Far Should a Carbon Monoxide Detector Be From a Furnace

Proper placement of a carbon monoxide (CO) detector near a furnace is critical to safety and to avoiding nuisance alarms. This article explains recommended distances, mounting height, code requirements, common placement mistakes, and practical tips to ensure reliable CO detection in American homes.

Location	Recommended Minimum Distance	Notes
From furnace or fuel-burning appliance	10–15 feet	Avoid mounting immediately adjacent to the appliance or on a vented duct to prevent false readings.
Outside sleeping areas	Within 10 feet of bedroom doors	NFPA recommends alarms be placed so occupants will hear them while sleeping.
Basement with furnace	On ceiling or high on wall, but 10–15 feet from unit	Basements often require a detector if a fuel-burning appliance is present.

Near The Furnace Room

Place a CO detector at least 10–15 feet from the furnace, mounted on the ceiling or high on the wall of the adjacent living space rather than inside the furnace room unless required by local code.

Bedrooms And Sleeping Areas

Install CO detectors outside and within 10 feet of sleeping room doors so alarms will wake occupants. This placement aligns with NFPA 720 guidance and improves the chances of timely evacuation.

Basement With Gas Furnace

Basements often contain fuel-burning equipment. Place a detector on the ceiling or high on the wall at least 10 feet from the unit. If the furnace is in an enclosed room with a door, placing the alarm outside the door is appropriate to ensure occupants hear it.

Multi-Level Homes

Install a CO detector on every level of the home where fuel-burning appliances are present or where people sleep. Ensure detectors are interlinked or audibly reachable from sleeping areas for maximum safety.

Sensor Types And Sensitivity Considerations

CO detectors use different sensor technologies—electrochemical sensors are common in home detectors for their stability and accuracy. Sensor drift, temperature, and humidity can affect performance.

Some detectors monitor time-weighted average concentrations and alarm at different thresholds depending on exposure duration. Proper placement helps sensors reflect meaningful changes in living spaces rather than brief startup spikes.

Installation Checklist

• Follow manufacturer instructions and local building codes first.
• Mount detectors at least 10–15 feet from the furnace and other fuel-burning appliances.
• Place detectors outside sleeping areas and on each occupied level.
• Mount on ceiling (6–12 inches from ceiling) or wall (4–6 feet from floor) per device guidance.
• Avoid drafts, vents, windows, doors, and dead-air zones.
• Test detectors monthly and replace batteries annually or as recommended.
• Replace CO detectors every 5–10 years depending on manufacturer specifications.

What To Do If The Detector Alarms

If a CO detector sounds, the following steps are recommended: evacuate occupants and pets, move to fresh air immediately, call 911 or the local emergency number, and do not re-enter until authorities declare it safe.

Seek medical attention for anyone experiencing CO poisoning symptoms such as headache, dizziness, nausea, shortness of breath, confusion, or loss of consciousness.

Testing, Maintenance, And Replacement

Routine maintenance ensures long-term reliability. Test alarms monthly using the test button, replace batteries yearly or when low-battery signals occur, and follow manufacturer guidance for cleaning and sensor replacement.

Most residential CO detectors have a service life of 5–10 years. Replace units at the end of their life to maintain accurate detection and compliance with safety recommendations.

Practical Examples And Scenarios

Example 1: A furnace in an open basement. Mount a detector on the ceiling of the first floor at least 10 feet horizontally from the furnace and within 10 feet of bedroom doors to meet NFPA guidance.

Example 2: A small utility closet housing a water heater. Place the CO detector outside the closet and 10–15 feet away from the closet door to avoid false alarms while ensuring prompt detection if CO enters living areas.

Frequently Asked Questions

Is 10 feet far enough from a furnace?

Yes. 10 feet is the widely referenced minimum distance to minimize nuisance alarms while still allowing timely detection, though 15 feet adds extra margin. Always consult the detector manual and local code.

Can a CO detector be in the furnace room?

Many experts advise against mounting a detector directly inside the furnace room because normal combustion appliance operation can trigger false alarms. If the furnace room is occupied or accessible and local codes require it, follow manufacturer guidance for placement.

Where should a CO detector be mounted in a basement?

Mount on the ceiling or high on a wall, at least 10 feet from the furnace, outside the furnace area if possible, and within audible range of sleeping areas above.

Final Practical Tips

• When in doubt, follow the manufacturer’s placement guidance and local building codes.
• Prefer multiple detectors to a single unit; placing CO alarms on each level and near sleeping areas ensures better coverage.
• Interconnected (hardwired or wireless) alarms increase the chance occupants hear warnings from any part of the home.
• Schedule annual inspections for fuel-burning appliances to reduce CO risk at the source.

Key Takeaway: Place carbon monoxide detectors at least 10–15 feet from furnaces and other fuel-burning appliances, install alarms outside sleeping areas and on every level, mount at recommended heights, and maintain devices regularly to ensure reliable early warning without nuisance alarms.