Carbon monoxide (CO) is often called the “silent killer” for a reason. It is colorless, odorless, invisible, and impossible to detect without a device.
CO is produced when fuel does not burn completely. That includes gas furnaces, water heaters, fireplaces, gas stoves, generators, and vehicles running in attached garages. Exposure can cause headaches, dizziness, nausea, confusion, and in severe cases, death.
Carbon monoxide detectors are essential. But just like smoke alarms, placement matters.
This guide explains where CO detectors should go in a typical U.S. house or apartment. Smoke and CO detectors have different placement rules, and you cannot assume one covers the other.
If you are in Northeast Ohio and prefer professional help, Colin Can Help offers smoke and carbon monoxide detector assessment and installation services. But whether you DIY or hire a pro, this guide will help you place CO alarms correctly.
High-Level Rules for Carbon Monoxide Detector Placement
A well-protected home should have:
- At least one CO detector on every level that has a fuel-burning appliance
- A CO detector outside sleeping areas or near bedrooms so it can wake occupants
- A CO detector near, but not directly next to, major fuel-burning appliances and attached garages
Many homes have zero CO detectors. Others have only one, even in multi-level homes with gas appliances and attached garages.
Where CO Detectors Should Go in the Home
Near Sleeping Areas
CO detectors should be close enough to bedrooms to wake people if an alarm sounds. In many homes, this means installed in the hallway outside bedrooms, or inside bedrooms if the layout is spread out.
If bedrooms are far apart on different levels, each sleeping area should have nearby CO detection. The goal is simple: if CO builds up at night, the alarm must be loud enough and close enough to wake you.
On Each Level of the Home
Carbon monoxide mixes with air and can spread throughout a level. Each level that contains fuel-burning equipment or sleeping areas should have a CO detector. Even if your furnace is in the basement, CO can travel upward through ductwork and stairwells.
Near Fuel-Burning Appliances
Common sources include gas furnaces, water heaters, gas dryers, gas stoves, fireplaces, wood stoves, and boilers.
A CO detector should be placed in the same general area or room, but not directly beside the appliance. Avoid mounting the detector right on top of a furnace or water heater. Brief startup emissions can cause nuisance alarms.
A good rule is to place it several feet away, in the same room or just outside it, following manufacturer distance guidelines.
Near or Above Attached Garages
Attached garages are one of the most common CO risks. Even a car running briefly in the garage can allow carbon monoxide to seep into the house.
Recommended placement:
- Just inside the home near the door connecting to the garage
- In rooms directly above the garage
CO can move through framing cavities and floor systems into bedrooms or living spaces above.
Height, Distance, and Do/Don’t Details
Unlike smoke, carbon monoxide does not rise to the ceiling. It mixes with air.
Wall vs Ceiling Mounting
Most CO detectors can be wall-mounted at normal breathing height or ceiling-mounted if manufacturer allows. Always follow the manufacturer’s instructions for your specific unit.
Recommended Distance Guidelines
Place CO detectors several feet away from fuel-burning appliances, away from bathrooms and laundry rooms with high humidity, and away from supply vents and return ducts. Airflow can delay or distort detection.
Avoid These Locations
Do not install CO detectors right next to exterior doors or windows, directly beside exhaust fans, inside unfinished garages, in bathrooms, or directly over sinks.
Special Situations and Layouts
Apartments and Condos
Install at least one CO detector near sleeping areas. If there is a gas appliance in the unit, ensure detection nearby. In buildings with shared systems, CO can travel between units.
Homes With Multiple Fuel-Burning Appliances on Different Levels
If you have a gas furnace in the basement, a gas fireplace on the main floor, and a gas water heater, you likely need CO detection on multiple levels. Each level with a fuel source or sleeping area should have coverage.
All-Electric Homes
If your home is fully electric with no gas appliances, you still need a CO detector if you have an attached garage, a wood-burning fireplace, or a portable generator used during outages. CO risk does not disappear just because your stove is electric.
Vacation Rentals and Airbnbs
Guests expect visible, working CO detection. Install near sleeping areas and ensure alarms are tested and documented. Proper placement protects guests and protects you as the owner.
Common CO Detector Placement Mistakes
- Only one CO detector in a multi-level home
- No detector near bedrooms
- Installing directly on top of a furnace
- Mounting next to drafty doors or vents
- Hiding the detector behind furniture
- Skipping rooms above attached garages
CO detectors must be accessible, audible, and unobstructed.
Example Layout Scenarios
Example 1: 2-Bedroom Apartment With Gas Furnace and Gas Stove
Recommended CO placement: 1 detector in hallway outside bedrooms, 1 detector near but not inside furnace closet area. Total: 2 detectors.
Example 2: 3-Bedroom Two-Story Home With Basement and Attached Garage
Basement: 1 detector near but not directly beside furnace. Main floor: 1 detector near door from garage into house. Upstairs: 1 detector in hallway outside bedrooms. Total: 3 detectors minimum.
How CO Placement Fits With Smoke Detector Placement
Smoke and CO alarms are not placed identically. There will be overlap near sleeping areas and on each level. But CO detectors do not need to be inside every bedroom, and smoke detectors should not be installed in garages.
Combination smoke/CO units can be useful in hallway and bedroom-adjacent areas, reducing the number of devices needed.
To complete your safety plan, read our separate guide on where smoke detectors should be installed.
DIY vs Professional Installation
When DIY Is Usually Fine
- Plug-in CO detectors
- Battery-powered units
- Installing in easy-to-reach locations
- Not modifying wiring
For a deeper look at the DIY question, see our article on whether you can install a smoke detector yourself – the same principles apply to CO detectors.
When to Call a Professional
Consider hiring a pro if you are installing hardwired or interconnected units, want combination smoke/CO systems, have a complex layout, are preparing for a home sale or rental inspection, or are unsure if your coverage is adequate.
If you are in Northeast Ohio, Colin Can Help can assess your home, recommend proper CO detector locations, and install or replace them in one visit.
Next Steps
Now is a good time to walk through your home and identify where CO detectors are missing, check the manufacture date on any existing CO alarms, and replace any unit approaching its rated lifespan. If you are unsure whether a sealed or long-life unit makes sense, read our guide on whether 10-year detectors are worth it.
To go deeper:
- Read our CO detector types guide to compare plug-in, battery, hardwired, combo, and smart options
- Review our maintenance and testing guide to understand how often to test and replace CO alarms
- Revisit our smoke detector placement guide to ensure complete fire and gas protection
For a complete overview of smoke and carbon monoxide detector safety, visit the Colin Can Help smoke and carbon monoxide detector guide.