GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Where is the best place to put a carbon monoxide detector in a home?

GBA Editor | Posted in General Questions on

I was told that they should be placed really low because carbon monoxide is heavier than air.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Armando Cobo | | #1

    The gravity of air is 1 and the gravity of Carbon Monoxide is .9657 (per the EPA), which is almost identical; however since CO is usually mixed with warm air expelled by the appliances, it tends to rise with the warm air. Therefore, you should install all CO detectors up high, centrally located outside all your sleeping areas, on every floor of your home, in or near any attached garage and any other location per manufacturer’s instruction. You should never install a CO detector near fuel burning appliances and make sure they are replaced every five years.

    [Editor's note: For more information on carbon monoxide and carbon monoxide detectors, see the following GBA articles:]

    A UL-Listed Carbon Monoxide Alarm May Not Protect You

    Judges Dismiss Cases Over Carbon Monoxide Deaths in Aspen

    Do Combustion Safety Testing Protocols Need Fixing?

    Fans in the Attic: Do They Help or Do They Hurt?

  2. Riversong | | #2

    Carbon Dioxide is heavier than air (as is propane). Because CO has nearly the same specific gravity as air, the alarms can be located either low (for plug-in units) or high on ceilings or 6" below ceiling on walls (avoid corners where air is dead).

    Do NOT install one in a garage as it will constantly alarm from the car exhaust. And do not install one in a kitchen with a gas range or you will also get nuisance alarms.

  3. John Klingel | | #3

    And don't install a sensitive smoke alarm near a toaster if anyone likes DARK toast. My wife sets ours off on a regular basis.

  4. jason green | | #4

    Well as per osha's regulations your supposed to check at three intrevals low mid and high because the concentrations can vary while some of these theories may be correct in some instances, however the truth is CO is heavier than Air molecules so it will fall the theory off hot rises is not always true heat will go to cold. although hot air will riseso CO is in a form of air so it too will rise there for a CO detector should always be put low, reason for that is it will come from below almost always, so rather then be exposed and killed by it before it reaches the ceiling you will be allerted by the alarm as it rises. SO the theory of CO detectors joined with smoke alarms is a good secondary alert you should always have an alert system to warn you before you are unable to get out of the threatined conclusion place the co detectors low, approxoutlet hight for the rechargable units in case of power outages is best

  5. Riversong | | #5

    Jason is incorrect on all counts. CO is slightly lighter than air, though not enough to make a difference. Warm air will always rise unless forced by mechanical pressure otherwise. OSHA has no authority over private homes, only workplaces. And fire codes require hardwired CO detectors to be placed on ceilings or high on walls. Plug-in detectors can be placed at outlet height.

  6. Danny Kelly | | #6

    In my opinion, the type of CO detector is more important than its location. It is best to get a detector with a digital readout - these can detect low levels on CO which most of the cheap ceiling mounted detectors cannot. These more sensitive detectors are typically the plug in type (so will be low on the wall). Long term exposure to low levels of CO can be very harmful and most of the ceiling mounted detectors are not programmed to go off until the CO level reaches 400ppm for a few hours. Levels as low as 35ppm can cause problems and these would go undetected with a typical ceiling mounted CO detector.

    These cheap options are basically programmed to only read levels high enough to cause death - over 1000ppm - at this level, the density of the gas really does not matter - very unlikely that you would have levels of 1000ppm high or low in the room and have levels so low they would be undetectable on the opposite surface.

    Best practice is to probably put in the hardwired ones in the ceiling and tie into the security system for casatrophic problems and then have an additional plug in type to detect low levels.

  7. jason green | | #7

    unfortunatly robert you did not read my answer well i was only stating that osha tells you to take these readings at different levels for the variabls but i am not wrong perhaps you should get more education on this point yes CO islighter then air and will rise when warmed but if your boiler is not running or heat isnt needed it will stay low these CO detectors mostly have a 4 hr exposure rate and i believe i put that the smoke detector/CO combo is a good secondary alert the best place is in an outlet like i said. please learn how to not contradict your own previous state ment in number two to try to sound like you know more then others i dont try to disagree with people because thier is always a different view and NO ONE knows every thin. So in conclusion again its best for the average alarm to be placed in the outlet, as for Mr. Kellly's input he is along the right lines as well many CO dtectors are not as good as the higher tech. digitals which are much more efficient to use but i would have one in both locations high for secondary alerts and low for your initial warning to get out or open windows to dillute the concentration .

  8. Mike | | #8

    Jason, you need to understand robert... he knows everything, he is never, ever wrong; he is intransigent and rude; he opines on every question and manages to insult anyone who disagrees with his way of doing things; the poor man can not help himself.

  9. Riversong | | #9


    Attacking the messenger because you don't like the message only diminished your own credibility.

    It's not that I'm never wrong, it's that I'm not foolish enough to address subjects I don't understand.

    Jason was wrong on every count, both in this response and in others he's posted on this forum.

  10. charlie | | #10

    Well, all you einstein's have got to buy a clue. You need to be able to afford to buy a CO2 detector before worrying about where to install the thing. In this recessive economy people need higher incomes to better their living standards. CO2 detectors should be located on the or near the ceiling and also about 18 to 24 inches above the floor considering that is the lowest level of the house or apt.

  11. Jack | | #11 indicates that placing them high, since the CO will be usually mixed with heated air, it will go with the warm air.

    Also the specific density of CO is reported by the EPA (related in the same article) as .9657 (relative to 'standard air' of 1.0? - not stated in the article), would indicate that CO will 'float', but it mixes so well with air, the bouancy should be considered 'negligible'. But if it did separate, it too would rise due to this bouancy. Due to the Brownian Motion, it should migrate throughout the 'clean air' even without convection eventually, being (due to the relative density) more concentrated higher, but it would be everywhere as time proceeds and the concentration grows.

    For me and mine, having both fire and CO sensors near the ceiling in sleeping areas makes most sense. If you have a REASON to think the CO is generated and let loose in the room will be near the floor, putting additional sensors in the area makes sense.

    I tried to look up the suggestions from manufacturers, OSHA, or whatever, and didn't find much 'official guidance'. If you are really worried, call your local health or fire department to get your local version of the 'right answer'. Getting an email from them you could archive, will also give you some credence if someone should ask or challenge your choice of installations. And if you do, please post to let us know.

    Also, there are combined devices that are CO and fire detectors.

    Take care...

  12. Kelly In Afghanistan | | #12

    well, ummm,....this is just something to ponder for the "Einstein Charlie" in post #10. Not sure if it was an innocent typo but when you come across sounding like the way i took it, you MIGHT want to get all of YOUR OWN info correct before possibly belittling someone else because it will come back to bite you. I don't see anywhere else in these posts did it mention CO2 Detectors?? CO detectors yes but NOT CO2!? Refresher 101; CO = Carbon Monoxide (Mono=1); CO2 = Carbon Dioxide (Di=2 or double). Now it's also true that they do in fact make CO2 detectors/sensors but it's for industrial processes which was not being discussed here. And the other, obvious CO2 would be the Fire Extinguisher type. Hope this heps clear things up for you and puts a smile on others faces! :O) Hope everyone has a safe day back in the states! Respectfully,...

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |