Carbon Monoxide Alarms: Placement and Testing

If an alarm is sounding now

Do not open windows and stay inside, and do not try to find the source yourself. After responders clear the house, keep the fireplace, stove or connected appliance off until the cause is found. Our guide to carbon monoxide and your chimney explains how a flue can let CO into a home.

Where alarms belong

The national guidance is consistent:

• Every level of the home, including the basement. The U.S. Consumer Product Safety Commission (CPSC) and NFPA both say this.
• Outside each sleeping area, in a central location. Alarms need to be close enough to wake sleeping people.
• Mounted as the maker says. NFPA advises following the manufacturer's instructions for placement and mounting height. Some models are made for walls, some for ceilings, and some plug into an outlet.

CPSC recommends battery-operated alarms or alarms with battery backup, so they keep working when the power is out.

A placement plan for an example house

This is a hypothetical house, used only to show how the guidance applies. It is a two-story home with a finished basement, a gas boiler and water heater in the basement, a wood-burning fireplace in the living room, bedrooms upstairs and an attached garage.

• Upstairs hallway. One alarm in the hall outside the bedrooms. If the bedrooms are spread out with separate hallways, each sleeping area gets its own.
• Main floor. One alarm on this level. A central spot such as a hallway or the living area serves the level; follow the alarm's instructions on distance from the fireplace and from kitchen appliances.
• Basement. One alarm on this level too, since the boiler and water heater are here and the basement may be used as living space.
• Connection. Interconnected alarms, wired or wireless, so an alarm in the basement also sounds upstairs where people sleep. CPSC and NFPA both describe interconnection as the best protection.

A ranch house with all the bedrooms on one floor would need fewer units. A house with a bedroom in the basement would need an alarm outside that bedroom as well.

Choosing an alarm

• Listing. New Jersey's fire code calls for CO alarms that are listed and labeled to UL 2034, the safety standard for residential CO alarms. Check the packaging or the back of the unit.
• Power. Battery-operated, plug-in and hard-wired alarms are all allowed under the New Jersey rule. Hard-wired and plug-in units should have battery backup.
• Combination units. A combined smoke and CO alarm is fine if it is labeled for both. A smoke alarm alone does not detect carbon monoxide.
• Display. Some alarms show a reading. That can be useful information for responders, but the alarm's job is the alarm. Do not wait for a number to climb before leaving.

Testing and upkeep

NFPA's advice is to test CO alarms at least once a month and replace them according to the manufacturer's instructions. A simple routine:

• Monthly: press the test button on each alarm and listen for it, and for the others if they are interconnected.
• When the battery chirps: replace the battery right away. A low-battery warning is easy to ignore for days.
• At the end of life: CO sensors wear out. Most alarms have a replacement date printed on them or an end-of-life signal described in the manual. Write the install date on the unit.
• After a storm: NFPA advises clearing snow from the outside vents of the dryer, furnace, stove and fireplace during and after a snowstorm. A buried vent can push exhaust back into the house.

Alarm, chirp or trouble signal

CO alarms can make more than one sound, and the manual for your model explains each one. In general:

• The alarm pattern means the sensor has detected carbon monoxide. Treat it as real: leave and call 911.
• A periodic chirp or trouble signal usually points to a low battery, a fault or the end of the alarm's life. NFPA advises checking the battery, replacing it if low, and calling the fire department if the trouble signal continues.

If you are not sure which sound you are hearing, assume it is the alarm and get outside.

After an alarm: getting back to normal

Once responders have checked the house and allowed you back in, a few steps help make sure the cause is found rather than guessed at:

• Write down the details. Which alarm sounded, the time, which appliances were running, the weather, and whether anyone felt ill. Wind, a snowstorm or a newly installed exhaust fan can all be part of the story.
• Keep the suspect appliances off. Ask responders or your gas utility which appliances should stay off until they are checked, and follow that.
• Have the venting checked. Have the appliance serviced and the flue it vents into inspected for blockage, damage and correct sizing. If an appliance was recently replaced, mention it; changes to a furnace or water heater can change what the chimney needs.
• Replace the alarm if it is old. If the alarm is near its end-of-life date, replace it, but do not assume a false alarm without a check.

What New Jersey requires when a home changes hands

Under the New Jersey Uniform Fire Code, a one- or two-family home, or an attached single-family home, must receive a certificate of smoke alarm, carbon monoxide alarm and portable fire extinguisher compliance before it is sold, leased or otherwise changes occupancy (N.J.A.C. 5:70-2.3). The rule says no CO alarm is required in a building that has no fuel-burning appliance and no attached garage.

Where CO alarms are required, N.J.A.C. 5:70-4.19 calls for single-station alarms in the immediate vicinity of the sleeping areas. They may be battery-operated, hard-wired or plug-in, must be listed to UL 2034, and are installed according to that section and NFPA 720.

The certificate is issued at the local level, and your fire official can tell you how the inspection works in your town. These rules set a minimum for a sale; the national guidance above, with alarms on every level, goes further. See also buying a home with a fireplace.

What an alarm cannot do

An alarm reports a problem after carbon monoxide is already in the air. It does not tell you why, and it cannot keep a blocked or damaged flue from producing the problem again tomorrow. NFPA recommends having fuel-burning heating equipment and chimneys inspected by a professional every year before cold weather. Annual checks of the furnace and boiler flue and the fireplace or stove flue address the source; the alarm covers the gap between visits.

Questions homeowners ask

Sources

1. U.S. Consumer Product Safety Commission: Carbon Monoxide Information Center
2. NFPA: Carbon Monoxide Safety tip sheet (copy hosted by the Village of Penn Yan, NY)
3. CPSC: Carbon monoxide alarm placement notice
4. N.J.A.C. 5:70-2.3, Certificate of smoke alarm, carbon monoxide alarm and portable fire extinguisher compliance (via Cornell LII)
5. N.J.A.C. 5:70-4.19, Smoke alarms and carbon monoxide alarms in one- and two-family dwellings (via Cornell LII)

This guide is general information. It can't diagnose a specific chimney; an inspection can.