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Knowing where to put carbon monoxide detectors matters as much as owning them. Carbon monoxide is a colorless, odorless gas, and a detector in the wrong spot can miss it entirely or go off so often that someone pulls the battery. With the heat about to run every day, now is the right time to check yours.
This guide covers why placement matters, how our own detectors are set up, the 6 rules for carbon monoxide detector placement, the spots where you should never install one, how to test and replace them, and exactly what to do if one goes off.
WHAT’S IN THIS GUIDE
Why Placement Matters
Carbon monoxide comes from anything that burns fuel: furnaces, gas water heaters, gas stoves, fireplaces, and cars or generators running in or near the house. More than 200 people in the U.S. die every year from accidental carbon monoxide poisoning linked to consumer products that aren’t fires. Source: U.S. Consumer Product Safety Commission — Carbon Monoxide Information Center
You can’t see, smell, or taste it, and the early symptoms, like headache, dizziness, nausea, and sleepiness, feel a lot like the flu. That’s why the detector has to be where it can catch the gas before it reaches the people in the house, especially while they’re asleep.
How Our Detectors Are Set Up
Our house has hardwired carbon monoxide detectors in two places: the living room on the main floor, and the upstairs hallway right outside the bedrooms. Neither one has ever gone off, which is exactly what you want.
That setup covers the two most important rules on the list below: a detector on each main living level, and one right outside where everyone sleeps. If you only do two things after reading this, check those two. Then walk through the rest of the rules, especially Rule 1. Every level of the house needs one, including a basement, and that’s the spot people miss most often.
Where to Put Carbon Monoxide Detectors: 6 Rules
Rule 1: Put one on every level of your home, including the basement
Install at least one carbon monoxide detector on every floor, including the basement. If your furnace or water heater is in the basement, that level especially needs its own detector. Source: Kidde — Carbon Monoxide Frequently Asked Questions
Rule 2: Put one outside every sleeping area
Carbon monoxide is most dangerous at night, when you’re asleep and can’t notice the symptoms. Install a detector in the hallway outside the bedrooms, within about 10 feet of each bedroom door, so the alarm is loud enough to wake everyone. If bedrooms are spread out across the house, each sleeping area needs its own. Source: Carrier — Best Carbon Monoxide Detector Placement
Rule 3: Put one near the door to an attached garage
A car warming up in an attached garage can push carbon monoxide into the house, even with the big garage door open. If a bedroom sits above or next to the garage, a detector near that room or near the door from the garage into the house is a smart addition.
Rule 4: Keep it at least 15 feet from fuel-burning appliances
Furnaces, water heaters, stoves, and fireplaces can give off a small puff of carbon monoxide when they first fire up. That’s normal, but a detector mounted right next to them can pick it up and cause false alarms. Keep detectors at least 15 feet away from fuel-burning appliances. Source: Kidde — Carbon Monoxide Frequently Asked Questions
Rule 5: Follow the manufacturer’s instructions for height
You’ll find conflicting advice about whether a CO detector should go high or low. Carbon monoxide mixes evenly with the air instead of rising like smoke or sinking, so the right height depends on the device. A combination smoke and carbon monoxide detector goes on the ceiling or high on the wall, where it can catch smoke. A plug-in CO detector can sit at an ordinary outlet. A standalone wall-mounted unit usually goes about chest height. The instructions that came with your detector are the final word.
Rule 6: Interconnect them if you can
Interconnected alarms all sound together when one detects a problem. If carbon monoxide builds up in the basement while you’re asleep upstairs, the upstairs alarm sounds too. Hardwired detectors are usually interconnected already. Some battery models can link wirelessly. Source: U.S. Consumer Product Safety Commission — Carbon Monoxide Information Center
Where Not to Put a CO Detector
A detector in the wrong spot can miss carbon monoxide or set off false alarms. Avoid installing one:
- Within 15 feet of a furnace, water heater, stove, or fireplace
- In a bathroom, where shower humidity can damage the sensor
- Next to an open window, door, vent, or fan, which can dilute the air the detector reads
- In a “dead air” spot, like a corner where the wall meets the ceiling, where air doesn’t move
- In direct sunlight
- Inside the garage itself, where car exhaust can set it off constantly
Source: Carrier — Best Carbon Monoxide Detector Placement
Hardwired, Plug-In, or Battery?
All three types work as long as they’re in the right place and they’re tested.
- Hardwired detectors run on your home’s electrical system with a battery backup, and they’re usually interconnected. They’re the most reliable, and that’s what we have. Replacing one with the same brand is usually a simple swap with the same wiring plug.
- Plug-in detectors go into a regular outlet and usually have a battery backup. They’re the easiest way to add coverage to a level that doesn’t have one, like a basement.
- Battery detectors can go anywhere. Many newer models have a sealed 10-year battery, so you never have to change it.
If you’re adding or replacing a detector on a level without wiring, a plug-in carbon monoxide detector with a digital display is the easiest option. The display shows the actual CO level, so you can see a low reading before it ever reaches the alarm point. For a hallway outside the bedrooms, a combination smoke and carbon monoxide detector covers both dangers with one device. If you’re replacing hardwired units, a hardwired smoke and carbon monoxide combo detector with battery backup keeps your Interconnected system intact. Match the brand of your current detectors so the wiring plug fits.
How to Test and When to Replace
A detector only protects you if it works. Keep yours that way:
- Press the test button at least once a month. You should hear a loud pattern of beeps.
- On hardwired and plug-in models, replace the backup battery once a year, unless the unit has a sealed 10-year battery.
- Check the date printed on the back of each detector. Most carbon monoxide detectors last 7 to 10 years, and then the sensor wears out and the whole unit needs to be replaced.
- Learn the difference between beeps. A single chirp every minute or so usually means a low battery. Many detectors also have a separate end-of-life chirp that means it’s time for a new unit. Check your manual so you know which is which.
If you’re replacing your smoke detectors anyway, our guide on how to replace smoke detectors walks through the process, and if yours have turned yellow with age, here’s why smoke detectors turn yellow and what it means. Source: Kidde — Carbon Monoxide Frequently Asked Questions
What to Do If Your CO Alarm Goes Off
Treat every carbon monoxide alarm as real:
- Get everyone, including pets, out of the house and into fresh air right away
- Call 911 from outside
- Don’t go back in until emergency responders say it’s safe
- Have a licensed professional inspect your furnace, water heater, and other fuel-burning appliances before you use them again
Source: Kidde — Carbon Monoxide Frequently Asked Questions
Most carbon monoxide problems start with a fuel-burning appliance that isn’t working right, so an annual furnace inspection is one of the best ways to prevent one. If your furnace is acting up, our guide on what to check when your furnace is not turning on covers the safe first steps. And never run a generator, grill, or car inside the house or garage, even with the door open. More than half of the consumer-product carbon monoxide deaths tracked by the CPSC are linked to portable generators. Source: U.S. Consumer Product Safety Commission — Carbon Monoxide Information Center
Using a fireplace this winter? Here’s how to get your fireplace ready for winter safely.
Frequently Asked Questions About Carbon Monoxide Detector Placement
Should a carbon monoxide detector be high or low on the wall?
It depends on the detector. Carbon monoxide mixes evenly with the air, so height matters less than location. Combination smoke and CO detectors go on the ceiling or high on the wall. Plug-in models work fine at a regular outlet. Always follow the instructions that came with your detector.
How many carbon monoxide detectors do I need?
At least one on every level of your home, including the basement, plus one outside each separate sleeping area. A two-story home with a basement and all the bedrooms upstairs usually needs at least three.
Should I put a carbon monoxide detector near my furnace?
Not right next to it. Put one on the same level as the furnace, but at least 15 feet away. Too close, and the normal startup puff can trigger false alarms.
Does a smoke detector detect carbon monoxide?
Not unless it’s a combination unit. A standard smoke detector only senses smoke. Check the label. A combination detector will say smoke and carbon monoxide (or smoke and CO) on the front or back.
Can I put a carbon monoxide detector in the bedroom?
Yes. A detector inside a bedroom is fine, and it’s a good idea if someone sleeps with the door closed or the bedroom is far from the hallway detector. The minimum is one in the hallway outside the sleeping area.
How long do carbon monoxide detectors last?
Most last 7 to 10 years. Check the manufacture date on the back of the unit. When it reaches the end of its life, it will usually chirp with an end-of-life warning, and the whole detector needs to be replaced, not just the battery.