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Carbon Monoxide Alarm Placement and Testing
Carbon monoxide has no smell, color or taste, so an alarm is the only way most people will know it is there. Where the alarms go, how often you check them and when you replace them matter as much as owning them.
The short answer: Put a working CO alarm on every level of the home and near every sleeping area, test it on a regular schedule, and replace it following the manufacturer's instructions or about every five years. If it sounds, get everyone outside into fresh air and call 911.
Why an alarm matters even if you have a clean chimney
Carbon monoxide, or CO, forms whenever fuel burns without enough oxygen. The CDC lists the usual household sources: furnaces, water heaters, gas ranges, fireplaces and wood stoves, portable generators, grills, and vehicles running in an attached garage. Blocked chimneys are on the list too, because exhaust that cannot leave the house has nowhere to go but inside.
A well-maintained chimney lowers the risk but does not remove it. CSIA points to damaged or deteriorating flue liners, soot buildup, debris and animal nests as ways a flue can block or leak exhaust, and notes that newer high-efficiency furnaces vented into old flues can perform poorly. Houses sealed tightly for energy savings can also starve appliances of the air they need.
Symptoms resemble the flu: headache, dizziness, weakness, upset stomach, chest pain and confusion. The CDC warns that people who are asleep, intoxicated or otherwise impaired can be harmed before they notice symptoms. That is why the alarm has to sit where the sleeping people are.
Where alarms go
The two federal agency sources agree on the basics. The CDC advises a CO alarm near every sleeping area. The Consumer Product Safety Commission advises alarms on every level of the home and outside sleeping areas, using battery-operated alarms or alarms with battery backup.
- Outside each sleeping area. If bedrooms open onto one hallway, an alarm in that hallway can cover them. Separate bedroom wings or floors each need their own.
- On every level, including the basement where a furnace, boiler or water heater often sits, and any level above an attached garage.
- Interconnected where possible. CPSC notes that when interconnected alarms are used, one sounding makes them all sound, so a problem in the basement wakes people upstairs.
- Follow the instructions for that model. Manufacturers give their own advice on height, distance from appliances and areas to avoid, such as very humid rooms. Read the leaflet that came with the alarm.
Avoid placing alarms where furniture or curtains cover them, and keep them clear of dust and paint.
About New Jersey rules. New Jersey’s Division of Codes and Standards publishes CO alarm requirements for hotels and multiple dwellings, where alarms must be within 10 feet of sleeping areas and meet the UL 2034 standard. Those rules apply to specific building types. Your local fire official or construction code office can tell you what applies to your home.
Battery, plug-in and hardwired alarms
The New Jersey document notes that alarms may be battery-operated, hardwired or plug-in, and that electrically powered units should have their own unswitched circuit so a wall switch cannot cut their power. For most homeowners the practical point is simpler: choose a unit with a battery backup, because carbon monoxide risk often rises during storms and outages, when furnaces cannot run and people turn to generators and fireplaces for heat.
- Battery only: Easy to place, but depends on you remembering to check the batteries.
- Plug-in with battery backup: Convenient and keeps working in an outage, but it needs an outlet in a good location.
- Hardwired with battery backup: Usually installed by an electrician; interconnection is common.
- Models with a digital display: The CDC notes that a digital readout can show the highest CO level recorded in the home, which is useful information to share with a technician after an incident.
Testing and replacement calendar
The CDC advises checking CO detector batteries when you change your clocks each spring and fall. That is a convenient reminder, but a calendar tied to the clocks is the minimum, not the whole routine. A sensible schedule looks like this:
| When | What to do |
|---|---|
| Monthly | Press the test button on each alarm, and confirm the sound is clear. Follow the model’s own instructions if they differ. |
| Spring and fall clock changes | Check or replace batteries, per the CDC’s advice. |
| Start of heating season | Test every alarm again, and have heating appliances and the chimney inspected before you rely on them. |
| After a storm or power outage | Confirm alarms are working, especially before running a generator or fireplace. |
| Manufacturer’s date, or about every 5 years | Replace the alarm. The CDC says to replace detectors following the manufacturer’s instructions or every five years. |
The monthly test is a recommendation common in manufacturer instructions rather than something the sources above set out, so check your model’s leaflet. Many alarms show an end-of-life date or sound a specific chirp. The signals differ by model, so keep the instructions.
The CDC suggests setting a calendar reminder at the time you install the alarm. Writing the install date on the back with a marker also helps.
What to do when it sounds
Treat a CO alarm as real until proven otherwise. The CDC page does not spell out a response procedure, and CPSC’s advice for suspected poisoning is the clearest official wording: get outside to fresh air immediately, then call 911. A sensible sequence for a household:
- Move everyone, including pets, outside into fresh air. Do not stop to open windows or find the source.
- Call 911 or your emergency number from outside. Say that a CO alarm is sounding, and report any symptoms.
- Stay out until responders say it is safe. Do not go back in to silence the alarm.
- Do not use the suspect appliance again until it has been checked. That may be a furnace, water heater, stove, fireplace or generator.
- If a fireplace or wood stove is a possible source, a qualified chimney professional can inspect the flue and connector for blockages or damage.
If symptoms such as headache, dizziness or nausea are present, get medical attention. These symptoms can fade once you are in fresh air, but that does not mean the exposure was harmless.
How this connects to your chimney
An alarm tells you something is wrong. It does not tell you why. When the cause may be a fireplace, stove or furnace flue, the next step is a look at the venting path. A chimney inspection can check for blockages, nests, deteriorated liners and gaps, and our guide on carbon monoxide and your fireplace explains the connections in more detail. If you already notice signs to stop using your fireplace, such as smoke in the room or a blocked flue, stop burning until the system has been checked.
This guide cannot say what level of CO is dangerous in your home, how to interpret a specific alarm model’s readings, or whether your appliances are venting correctly. Those are questions for the alarm manufacturer, emergency responders, the gas utility or a qualified technician.
Frequently asked questions
How many CO alarms does a house need?
At minimum, one outside each sleeping area and one on every level, per the CDC and CPSC. Larger or multi-wing homes may need more. Check your local requirements with the fire official or construction code office.
Can I silence the alarm and go back inside?
No. Go outside first and call 911. Return only when responders say it is safe.
How long does a CO alarm last?
The CDC says to replace it following the manufacturer's instructions or every five years. Many alarms signal their end of life with a model-specific alert.
If my chimney was just cleaned, do I still need alarms?
Yes. CO can come from many sources, and a chimney problem can develop between visits.
Related reading
- Carbon monoxide and your fireplace
- Signs to stop using your fireplace
- Seasonal chimney maintenance in NJ
- Chimney inspection
Sources
- CDC, About Carbon Monoxide: placement near sleeping areas, battery checks at clock changes, replacement every five years, symptoms and sources
- CPSC, Carbon Monoxide Information Center: alarms on every level, interconnection, and getting to fresh air then calling 911
- NJ DCA, Carbon monoxide alarm requirements: NJ requirements for hotels and multiple dwellings, alarm types and the UL 2034 standard
- CSIA, avoiding carbon monoxide hazards: chimney and venting conditions that can leak or block exhaust
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