Quick Answer: Where to Place CO Detectors
- âś“On every level of your home (basement, main floor, upstairs)
- âś“Within 10 feet of every bedroom (hallways outside sleeping areas)
- âś“Near your furnace or attached garage (common CO sources)
- âś“5+ feet from fuel-burning appliances (avoid false alarms)
- âś“Mounted on wall or ceiling (CO mixes with air at all heights)
Minimum requirement: Most building codes require at least one CO detector per floor, with additional units near sleeping areas. For maximum protection, install more than the minimum.
Why CO Detector Placement Actually Matters
Carbon monoxide is an invisible, odorless gas that can kill within minutes at high concentrations. Unlike smoke (which rises), CO has roughly the same density as air, meaning it disperses throughout your home at all levels. But here's the critical detail most people miss: CO concentration isn't uniform.
How CO Spreads Through Your Home:
CO Starts at the Source
Malfunctioning furnaces, blocked chimneys, idling cars in garages—these create concentrated pockets of CO that spread outward. The gas doesn't instantly fill your entire home uniformly. It builds up near the source first, then disperses through air circulation.
Bedrooms Are Most Dangerous
Most CO deaths happen at night while people are sleeping. You can't smell CO. You can't see it. Your body's warning system (feeling dizzy, nauseous) shuts down while you sleep. A detector 15 feet from your bedroom might alarm too late—after you've already inhaled dangerous levels.
Time Is Everything
At 400 ppm (parts per million), CO causes headaches in 1-2 hours and death in 3 hours. At 800 ppm, you have 45 minutes before losing consciousness. At 1,600 ppm, you have 20 minutes. At 3,200 ppm, death occurs in 5-10 minutes. Every second counts. Detectors near sleeping areas give you those critical extra minutes to evacuate.
Why "One Per Floor" Isn't Enough
Building codes mandate minimum standards—not optimal protection. A single detector on your main floor might not alarm fast enough to wake you on the second floor if the furnace malfunctions. The detector will eventually alarm, but by then you may have been exposed to dangerous levels for 15-30 minutes. Install detectors where you SLEEP, not just where the law says you must.
Room-by-Room CO Detector Placement
Bedrooms & Sleeping Areas
Best Placement:
- • In the hallway outside bedrooms (within 10 feet of bedroom doors)
- • If bedrooms are on opposite ends of a hallway, install two detectors
- • Master suites with attached bathrooms: install inside the bedroom itself
- • Children's rooms: prioritize detector placement here—kids are more vulnerable to CO
Mounting Options:
Ceiling mount: Center of ceiling or within 12 inches of wall junction
Wall mount: 5 inches below ceiling (not near corners where air stagnates)
Plug-in units: Install in outlet 12-24 inches above floor (not behind furniture)
Why this works: Detectors in sleeping areas give you the earliest possible warning when you're most vulnerable. Sound carries easily down hallways, so one detector can protect multiple bedrooms if they're close together.
Kitchen
Best Placement:
- • 10-15 feet from gas stove or oven (prevents false alarms from cooking)
- • If kitchen is open-concept, install detector in adjacent living/dining area
- • For closed kitchens, mount on wall near exit doorway
- • Keep away from range hood exhaust (air turbulence causes false readings)
⚠️ Common Mistake: Too Close to Stove
Gas stoves produce small amounts of CO during normal operation—not dangerous but enough to trigger sensitive detectors. Installing too close (under 5 feet) causes nuisance alarms that train you to ignore the detector. Keep distance but still within the kitchen zone.
Basement & Utility Room
Best Placement:
- • 15-20 feet from furnace (close enough to detect early, far enough to avoid false alarms)
- • If you have a water heater, install detector between furnace and water heater
- • For finished basements with bedrooms: follow bedroom placement rules above
- • Near stairway leading upstairs (CO can drift up into living areas)
- • If you have a wood stove or fireplace: 15 feet away, on same level
Pro tip: Furnace rooms see temperature extremes and humidity. Choose a detector rated for 40-100°F operation. Battery-only units may fail in cold basements—consider hardwired models with battery backup.
Garage (Attached or Detached with Living Space Above)
Best Placement:
- • On the wall shared between garage and house (inside the house, not in garage)
- • If you have living space above garage: install detector at top of stairs leading down
- • For detached garages with workshops: install inside near door to house
- • Never install CO detector inside the garage itself—extreme temperatures damage sensors
⚠️ Critical: Attached Garages Are High-Risk
Idling cars in attached garages kill dozens of Americans annually. CO seeps through shared walls, door gaps, and ductwork into living spaces. Even with the garage door open, starting your car and letting it warm up creates dangerous CO levels. A detector on the house side of the shared wall catches this infiltration early.
Living Room & Common Areas
Best Placement:
- • For homes with fireplaces: 15-20 feet from fireplace opening
- • In central areas where family spends most time (increases chance of early detection)
- • Multi-story homes: install on main floor even if you have basement and bedroom detectors
- • Open-concept spaces: install in center of space, away from windows and HVAC vents
Fireplace users: Annual chimney inspections are critical. Blocked chimneys cause CO to backdraft into your home. Your detector will alarm, but prevention is better. Have chimneys cleaned and inspected every year before winter.
Where NOT to Install CO Detectors
Improper placement doesn't just reduce effectiveness—it causes false alarms that train you to ignore your detector. Avoid these locations:
❌ Never Install CO Detectors Here:
Within 5 Feet of Fuel-Burning Appliances
Furnaces, water heaters, gas stoves, fireplaces—all produce trace CO during normal operation. Too close = constant false alarms. Keep 15-20 feet distance for accurate readings.
Near HVAC Vents, Fans, or Drafty Areas
Air circulation dilutes CO concentration before the detector can measure accurately. Also avoid mounting near ceiling fans, exhaust fans, or open windows. Dead air spaces (corners, behind doors) are equally bad—CO can't reach the sensor.
In Unconditioned Spaces (Garages, Attics, Crawl Spaces)
CO detectors have operating temperature ranges (usually 40-100°F). Extreme heat or cold damages sensors and causes false alarms. Never install in unheated garages, hot attics, or damp crawl spaces. Install on the conditioned (heated/cooled) side of walls.
In Bathrooms or High-Humidity Areas
Steam and humidity interfere with electrochemical sensors (the type used in most CO detectors). Install detectors outside bathrooms, not inside. Laundry rooms with dryers are borderline—mount detector away from direct steam/moisture.
Directly Above or Below Windows and Doors
Drafts from windows/doors create false negatives (CO blown away before detection) or false positives (outdoor air contamination). Mount detectors at least 3 feet from windows and exterior doors.
Near Fresh Paint, Solvents, or Strong Cleaning Chemicals
VOCs (volatile organic compounds) from paint, paint thinner, bleach, ammonia, and aerosols can trigger false alarms. Don't install detectors in rooms you've recently painted. Wait 48 hours for fumes to dissipate before installing.
Tricky Scenario: Kitchens with Gas Appliances
This is the #1 source of false alarms. Gas ranges and ovens produce small amounts of CO during normal use—typically 5-15 ppm, well below dangerous levels. But if your detector is 3 feet from the stove, it might alarm during Thanksgiving dinner when the oven's been running for hours. Solution: Install 10-15 feet away in adjacent room or at kitchen entrance. You'll still get warned if levels spike dangerously, but won't get nuisance alarms from normal cooking.
How Many CO Detectors Do You Actually Need?
Building codes specify minimums. Smart homeowners exceed them. Here's a realistic assessment:
Recommended Number by Home Size:
Small Home / Apartment (Under 1,200 sq ft)
1 bedroom, single level or 2 levels close together
- • 1 near bedroom(s)
- • 1 on main level near fuel-burning appliances
- • 1 in basement if applicable
Medium Home (1,200-2,500 sq ft)
2-3 bedrooms, 2 levels
- • 1-2 upstairs (hallway outside bedrooms, or 1 per bedroom cluster if bedrooms are far apart)
- • 1 on main floor living area
- • 1 in basement near furnace
- • 1 near attached garage entrance (if applicable)
Large Home (2,500-4,000 sq ft)
4+ bedrooms, 2-3 levels, multiple fuel-burning appliances
- • 2-3 on upper level (master bedroom, kids' wing, guest rooms)
- • 2 on main floor (living area, kitchen/dining area)
- • 1-2 in basement (furnace room, finished basement living space if applicable)
- • 1 near garage entrance
Very Large or Multi-Family Home (4,000+ sq ft)
5+ bedrooms, 3+ levels, complex HVAC systems
- • 1 detector per bedroom or per 1,000 sq ft of living space
- • Additional detectors near each major appliance zone
- • Consider interconnected/smart detectors for whole-home alerts
Cost Reality Check:
That's $125-250 to protect your family from the #1 cause of accidental poisoning deaths in America. Less than a month of cable TV. Less than a single ER copay if someone gets poisoned. Install more detectors than you think you need.
Don't Skimp on Bedrooms
If you're on a tight budget and can only afford 3-4 detectors, prioritize sleeping areas over utility rooms. You're awake during the day and can smell gas leaks, see smoke, feel dizzy from CO exposure. At night, you're unconscious. The detector outside your bedroom is the one that saves your life. Don't cheap out here.
Installation Tips: Getting It Right the First Time
Step-by-Step Installation Process:
Read the Manufacturer's Instructions
Every detector is slightly different. Some specify 5 feet from combustion sources, others say 15 feet. Some work on walls, others need ceiling mounting. Check the manual before drilling holes.
Test the Detector Before Installing
Insert batteries (if battery-powered) and press the test button. Make sure it chirps loudly—at least 85 decibels. If it sounds weak or doesn't work, return it before mounting. Don't install a dead detector.
Mark Your Location
For wall mounts: Use a level to mark horizontal line 5 inches below ceiling. For ceiling mounts: Find a ceiling joist with a stud finder (for secure mounting). Mark pencil dots for screw holes.
Mount the Base Plate
Most detectors have two parts: a mounting plate and the detector unit. Screw the plate to the wall/ceiling first. Use drywall anchors if not hitting a stud. Make sure it's level and flush—crooked detectors look unprofessional.
Attach the Detector Unit
Twist or clip the detector onto the base plate (varies by model). You should hear/feel it lock into place. Give it a gentle tug to confirm it's secure. For plug-in units, just insert into outlet—no tools needed.
Test Again After Installation
Press the test button. If it doesn't alarm loudly, check battery connection or wiring (for hardwired units). Test weekly for the first month to ensure it's working properly. Then test monthly going forward.
Write Installation Date on Detector
CO detectors expire after 5-7 years (electrochemical sensors degrade over time). Use a permanent marker to write the installation date on the back or side. Set a phone reminder to replace it in 7 years.
âś“ Hardwired vs Battery: Which is Better?
Hardwired with battery backup: Best option. Never dies from dead batteries, but has backup power during outages. More expensive and requires electrical work ($80-150 per unit installed).
Battery-only: Cheaper ($25-40) and DIY-friendly. Choose 10-year sealed lithium battery models so you never have to change batteries. Just replace the entire unit after 10 years.
âś“ Interconnected Alarms: Worth It?
Interconnected detectors (hardwired or wireless) all alarm simultaneously when one detects CO. This is critical in large homes—if the basement detector alarms, you'll hear it upstairs. Costs $150-300 to retrofit existing home, but worth it for multi-level homes or houses over 2,500 sq ft.
Maintenance Schedule: Keep Your Detectors Working
CO detectors aren't install-and-forget devices. Sensors degrade, batteries die, dust accumulates. Follow this maintenance schedule:
đź“… Monthly: Test Button Check
Press the test button on each detector. It should chirp loudly (85+ decibels). If it's weak or silent, replace batteries or the entire unit.
Pro tip: Pick a consistent date each month (like the 1st) so you don't forget. Add a phone reminder.
🧹 Every 6 Months: Vacuum/Dust
Use a vacuum with a brush attachment to gently clean detector vents. Dust and cobwebs block airflow to the sensor, causing false readings. Takes 30 seconds per detector.
🔋 Annually: Replace Batteries (If Applicable)
For detectors with replaceable batteries, swap in fresh ones every year. Do it when you change clocks for daylight saving time (easy to remember). Use quality alkaline batteries—cheap batteries leak and damage detectors.
Exception: 10-year sealed battery units don't need battery changes. Just replace the entire unit after 10 years.
🔄 Every 5-7 Years: Replace the Entire Detector
Electrochemical sensors degrade over time. Check your detector's manual for its specific lifespan (usually 5-10 years). When it expires, throw it away and install a new one. Don't try to extend its life— expired sensors give false negatives.
⚠️ What If You Hear Random Chirping?
Single chirps every 30-60 seconds usually mean:
- • Low battery: Replace batteries immediately
- • End-of-life warning: Detector is 7+ years old and needs replacement
- • Sensor malfunction: Unit is damaged or defective—replace it
Never ignore chirping. Homeowners get used to the sound and tune it out. A chirping detector is a broken detector. Fix or replace within 24 hours.
Building Code Requirements by State
CO detector requirements vary by state. Some mandate them in new construction only, others require retrofitting existing homes. Here's what you need to know:
Common Code Requirements (Most States):
- •One detector per floor of the home (basement, main floor, upper floors)
- •One detector within 10-15 feet of each bedroom or sleeping area
- •Detectors must meet UL 2034 standards (all modern CO alarms do)
- •New construction: Hardwired detectors with battery backup required in most states
- •Existing homes: Battery-powered acceptable, but some states now require hardwired during renovations
States with Strictest CO Detector Laws:
California
Required in all homes (new and existing). Must be within 10 feet of bedrooms. Landlords must provide and maintain detectors in rental properties.
New York
Mandatory in all homes with fuel-burning appliances or attached garages. Battery-powered acceptable in existing homes, hardwired required for new construction.
Colorado
Required on every level and within 15 feet of sleeping areas. Combination smoke/CO alarms allowed.
Massachusetts
One of the first states to mandate CO detectors (2006). Required on every floor and near bedrooms in all homes, including apartments.
Illinois
Required within 15 feet of sleeping areas in homes built after 2007. Battery-powered acceptable for existing homes.
Florida
Required in new construction (2008+) near bedrooms. Existing homes not mandated but strongly recommended.
Landlord Responsibilities
In most states with CO detector laws, landlords are required to:
- • Install CO detectors in all rental units with fuel-burning appliances or attached garages
- • Provide working detectors at move-in (with fresh batteries)
- • Replace broken or expired detectors within 48-72 hours of notice
- • Tenants are typically responsible for routine battery changes
If you're renting and your landlord won't install CO detectors, check your state's tenant rights laws. Many allow you to install detectors yourself and deduct the cost from rent.
Best CO Detectors for Different Needs
Not all CO detectors are created equal. Here are top picks for different scenarios:
First Alert CO400 Battery-Powered
Best budget option for basic protection
~$20
View on Amazonâś“ Pros:
- • Cheapest reliable detector on market
- • Uses 2 AA batteries (easy to replace)
- • 85 dB alarm (loud enough to wake you)
- • UL 2034 certified
âś— Cons:
- • Batteries need annual replacement
- • No digital display (just alarm)
- • 7-year sensor life (then replace unit)
Best for: Budget-conscious homeowners, apartments, rental properties. Buy in bulk (6-pack) to equip entire home for $120-150.
Kidde 10-Year Worry-Free Sealed Battery
Best set-it-and-forget-it option
~$50
View on Amazonâś“ Pros:
- • Never change batteries—10-year lithium sealed cell
- • Digital display shows CO levels in ppm
- • Peak level memory (shows highest reading)
- • 85 dB alarm
âś— Cons:
- • Higher upfront cost ($50 vs $20)
- • Can't replace battery—must replace entire unit after 10 years
Best for: Homeowners who forget to change batteries, vacation homes, elderly relatives' homes. The digital display is helpful for peace of mind—you can see actual CO levels, not just an alarm.
First Alert Plug-In with Battery Backup
Best for utility rooms and kitchens
~$35
View on Amazonâś“ Pros:
- • Continuous power from outlet (no battery changes)
- • Battery backup for power outages
- • Digital display with peak reading
- • Easy installation (just plug in)
âś— Cons:
- • Requires accessible outlet (not ideal for ceilings)
- • Can be unplugged accidentally or by kids
- • Backup batteries still need replacement every 2-3 years
Best for: Basements, garages, utility rooms where outlets are plentiful. Not recommended for bedrooms (you want ceiling/wall mount there).
First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
Best smart home integration
~$120
View on Amazonâś“ Pros:
- • Smartphone alerts (even when away from home)
- • Voice warnings ("Carbon monoxide detected in basement")
- • Wireless interconnection (all alarms sound together)
- • Split-spectrum smoke + CO in one unit
- • Nightly sensor checks (tells you status)
âś— Cons:
- • Expensive ($120 each, need multiple for whole home)
- • Requires WiFi and Nest app setup
- • 10-year sensor life, then replace entire $120 unit
Best for: Tech-savvy homeowners, large homes needing interconnected alarms, frequent travelers who want remote monitoring. The smartphone alerts are invaluable if you're away and want to know your house is safe.
đź’ˇ Our Recommendation: Mix and Match
You don't need to buy all the same model. Use 10-year sealed battery units in bedrooms (set and forget), plug-in models in basements/utility rooms (continuous power near appliances), and budget battery units in less critical areas. Total cost for a 2,000 sq ft home: $150-250 for 5-6 detectors of mixed types.
Common Questions About CO Detector Placement
Should I mount CO detectors on the ceiling or wall?
Either works—CO mixes evenly with air at all heights (unlike smoke, which rises). Ceiling mounting is slightly preferred because it keeps detectors out of reach of kids and pets, but wall mounting 5 inches below the ceiling works equally well. Follow your detector's manual for specific placement guidance.
Can I combine smoke and CO detectors?
Yes, combination smoke/CO alarms are a great space-saving option. They provide both protections in one unit. However, smoke detectors need ceiling mounting (smoke rises), while CO detectors work on walls or ceilings. Combination units should be ceiling-mounted for optimal smoke detection. You may still need additional standalone CO detectors near fuel-burning appliances.
Do I need CO detectors if I have an all-electric home?
If you have zero fuel-burning appliances (no gas furnace, water heater, stove, fireplace, wood stove) AND no attached garage, you technically don't need CO detectors. However, most building codes still require them, and they're cheap insurance. Generators, space heaters, and even a neighbor's attached garage can be sources. Install them anyway.
How close should the detector be to my bedroom?
Within 10 feet of the bedroom door is ideal. This gives you maximum early warning. Some people install detectors inside bedrooms themselves (especially master suites), which is fine—just avoid placing directly above the bed where false alarms would be jarring.
Will my CO detector go off from a running car in the driveway?
No, outdoor CO dissipates rapidly in open air. Your detector only measures indoor air. However, if you idle a car in an attached garage (even with door open), CO can seep into your home and trigger the detector. Never idle vehicles in garages—carbon monoxide builds up faster than ventilation can remove it.
Can I use the same detector for propane and CO?
No. CO detectors and propane/natural gas detectors are completely different devices. CO detectors use electrochemical sensors to detect carbon monoxide (a combustion byproduct). Gas detectors use catalytic sensors to detect explosive gas leaks. You need separate detectors for each. CO detectors won't alarm for gas leaks.
What if my detector keeps false alarming?
Common causes: (1) Detector too close to fuel-burning appliance—move it 15-20 feet away, (2) Detector exposed to solvents, paint fumes, or cleaning chemicals—ventilate and test again after 24 hours, (3) End of life (7+ years old)—replace the entire unit, (4) Low battery—change batteries. If none of these solve it, the detector is defective—return it for a replacement.
Do I need detectors on every floor even if I only have one fuel-burning appliance?
Yes. CO from a basement furnace can spread to upper floors through ductwork, stairwells, and ceiling penetrations. You might not notice symptoms on the upper floor until CO has been building for 30-60 minutes. A detector on each floor gives you earlier warning as CO spreads upward.
Don't Wait Until It's Too Late
Carbon monoxide kills over 400 Americans every year. Proper detector placement is the difference between a life-saving alarm and a tragedy. Install detectors today.
Recommended: 10-year sealed battery models for bedrooms, plug-in with backup for basements