Carbon monoxide detector placement

The other day I was helping a friend look over his home. His New home builder 1 year service warranty is approaching. There was a number of little things that were in need of fixing. I have a ? About the location of a Carbon monoxide detector. It’s mounted on the ceiling in a small hallway next to an attic pull down staircase. There are 2 bedrooms and a bath off that hallway. Gas fired heat pump in attic. Gas fireplace in living room. Did not see any other CO detector. My understanding is that CO detectors should be around 5’ from the floor. I appreciate any help with this question.

There’s a myth that carbon monoxide alarms should be installed lower on the wall because carbon monoxide is heavier than air. In fact, carbon monoxide is slightly lighter than air and diffuses evenly throughout the room. Ceiling mounted is okay.

They should be:

  • Within 15 ft. of all sleeping rooms

  • On each level/floor of the home

  • Placed in accordance with manufacturer’s instructions
    Ceiling or wall mount is ok if approved by the manufacturer.

Maybe a typo but I have never seen one of these…
Not trying to be an ass, wanting to learn more about it if it does exists.

Thanks for the info Patrick

You are correct. Not a heat pump. Just a furnace

Carbon monoxide detector safety reminders

  • Install CO detectors at your knee height. Never position carbon monoxide detectors on the ceiling like you would smoke detectors. Carbon monoxide blends with your home’s air and does not rise. Follow your manufacturer’s manual to properly install your detector at the right height. Remember to keep kids and pets in mind during installation.
  • Test the detector monthly. To ensure that your CO detector is working properly, test the detector every month. Most detectors include a one-press test button designed to shine a light or sound an alarm that the detector is working perfectly.
  • Keep the CO detector clean. You’ll want to make sure your detector is free of dust, dirt and other particles that may prevent the detector from spotting and alerting you of carbon monoxide. Wipe the detector with a cloth and vacuum it at least once a year or more as needed.
  • Listen for low-battery alerts. When your CO detector is low on batteries, it should automatically sound a repetitive high-decibel alarm alerting you to check the detector immediately. Even if it doesn’t, as a best practice, the U.S. Consumer Product Safety Commission advises changing your CO detector’s batteries annually when turning your clocks forward for Daylight Savings Time.

And the EPA (TAKE YOUR PICK! One says never on ceiling and one says on ceiling ok. I always put them about knee height, or so. But, read the manufacture’s package/instructions.):

Where Should I Place a Carbon Monoxide Detector?

Because carbon monoxide is slightly lighter than air and also because it may be found with warm, rising air, detectors should be placed on a wall about 5 feet above the floor. The detector may be placed on the ceiling. Do not place the detector right next to or over a fireplace or flame-producing appliance. Keep the detector out of the way of pets and children. Each floor needs a separate detector. If you are getting a single carbon monoxide detector, place it near the sleeping area and make certain the alarm is loud enough to wake you up.

•Carbon Monoxide Detectors Placement
CO detectors can monitor exposure levels, but do not place them:
Directly above or beside fuel-burning appliances, as appliances may emit a small amount of carbon
monoxide upon start-up; within 15 feet of heating and cooking appliances, or in or near very humid
areas, such as bathrooms; within 5 feet of kitchen stoves and ovens, or near areas locations where
household chemicals and bleach are stored (store such chemicals away from bathrooms and
kitchens, whenever possible);in garages, kitchens, furnace rooms, or in any extremely dusty, dirty,
humid, or greasy areas; in direct sunlight, or in areas subjected to temperature extremes. These
include unconditioned crawlspaces, unfinished attics, un-insulated or poorly insulated ceilings, and
porches; in turbulent air near ceiling fans, heat vents, air conditioners, fresh-air returns, or open
windows. Blowing air may prevent carbon monoxide from reaching the CO sensors.

•Do place CO detectors:
Within 10 feet of each bedroom door and near all sleeping areas, where it can wake sleepers. The
Consumer Product Safety Commission (CPSC) and Underwriters Laboratories (UL) recommend
that every home have at least one carbon monoxide detector for each floor of the home, and within
hearing range of each sleeping area;on every floor of your home, including the basement (source:
International Association of Fire Chiefs/IAFC); near or over any attached garage. Carbon monoxide
detectors are affected by excessive humidity and by close proximity to gas stoves (source: City of
New York); near, but not directly above, combustion appliances, such as furnaces, water heaters,
and fireplaces, and in the garage (source: UL); and on the ceiling in the same room as
permanently installed fuel-burning appliances, and centrally located on every habitable level, and in
every HVAC zone of the building (source: National Fire Protection Association 720). This rule
applies to commercial buildings.

Much appreciated. Thanks

Best procedure is to follow the manufacturer’s instructions. The molecular weight of air is 29, carbon monoxide is 28.01, close enough to spit. I hear that heavier than air crap all the time. Two factors that affect a gas distribution in a home are; dispersion (all gasses readily disperse into the surrounding gasses), and stack effect (air rising in a building due to thermal currents).

The major concern with a single, single station alarm (not interconnected with another alarm) is that it be audible from the sleeping areas (bedrooms) of the home. The idea is that occupants are most susceptible when they are asleep and that the air handler will distribute CO to the sleeping areas regardless of the origination point.

New laws in Maryland require a CO alarm on each level of all RENTAL properties. Why they haven’t required those alarms to be interconnected and hardwired is beyond me. The state Fire Marshall (Maryland) does recommend that CO alarms be combined with the hardwired interconnected smoke alarms as this gives the earliest possible warning and allows the most time to leave the building. Many landlords still opt for the single station alarms because its cheaper.

Winner! Winner! Winner!!!

code in MD & Pa is ceiling in a hall on sleeping floors, so depending if their is a 1st floor bedroom, 2nd floor hall is correct, more can be added, but code does not require more. Yes I am also a remodeling contractor in MD & Pa.

WE don’t inspect to code, however I do inspect RENTAL properties for the proper municipality. The law says ALL rental properties in Maryland (without respect to their local jurisdiction) must have a CO alarm on each level of the property including basements, must be less than ten years old and must have a tamper proof ten year battery.

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Patrick is absolutely correct. Also, Carbon monoxide is typically associated with heat sources and we all know that warm air (and CO) rises.

They can be placed either high or low and will function (read the mfr’s installation instructions). Mine are low, but if I was doing the initial placement, I would mount them high.

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bob, question for you? you stated all rentals need co smokes, my rental in Baltimore city is all electric and no garage! Code & health dept requires any electrical for the past decade or more to upgrade to hardwire all smokes, deemed it a safety issue! As a contractor in pa & md my experiences from all my inspectors is that only homes with fuel burning appliances or attached garages need co smoke, if I have been doing it incorrect for over a decade, let me know! Baltimore city is it’s own crap hole, if they require co smokes on every level, they are the only jurisdiction in the state, only sleeping level hall requires a co smoke per code!

You are correct about CO only required for fuel burning devices or attached garage. In April of 2018 House Bill 849 changed the CO law to apply to all rental properties in Maryland irregardless of the municipality (this is a State law that includes Baltimore City). The new law applies to rental properties having fuel burning appliances or an attached garage and specifically requires a CO alarm on each level of the property, excluding attics but including basements. At a minimum the alarms must have ten year tamper proof batteries and be less than ten years old.

This from the State Fire Marshal provides the most concise explanation.
17 Carbon Monoxide Alarm Requirement for Maryland Rental Properties.pdf (137.0 KB)

The new Baltimore City Rental Licensing guidelines cover this also on page 4 of the inspector guidance document (item F).
Inspection Checklist - Inspector Guidance Document.pdf (788.1 KB)

Mike Mohler sent this letter to current (at that time) Baltimore County landlords to reflect these changes.
MMohlerLetter.pdf (30.4 KB)


Absolutely correct. In Maryland fuel burning appliance(wood, gas, propane) require a CO monitor be installed on every level, with a sealed in lithium battery that is less than 10 years old.

guys, is this a brand new code?? I am a remodeler also, & code has always been 1 CO smoke on bedroom level only, wired into system with other smokes! Let me know, I will be doing inspections in MD soon & I still have my remodeling business, till the inspections in Pa & MD pays the bills fulltime.

Been a requirement since April of 2018. State law covers all jurisdictions for rental properties.

robert, I thought you guys were talking about owned homes! if that is code for rentals, HUD needs to enforce it in B-more, I would bet any amount of money that 90% of the city rentals don’t have operational smokes let alone a lithium CO smoke! I have zero plans on hanging out in the city inspecting rentals without my carry weapon! Good luck in the city that bleeds!