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I've got a Carbon Monoxide (CO) detector (BRK CO250B, instruction sheet PDF) that I am looking to install in our house. All of the bedrooms are on the top level of our quad-level house, and I'm planning on installing it in the hallway.

The directions say that it can be either ceiling or wall mounted. I've looked around online, and I've seen various recommendations for what the ideal height is for the detector.

  • Some say ceiling mounted is best, because CO is lighter than air. (Combination smoke/CO detectors all get mounted here.)
  • Some say that a few feet below ceiling height is best, because a pocket of warm air may prevent the CO from getting all the way up to the level of the detector.
  • Some say that "bed height," or 2-3 feet off the floor is best, because that is where you are when you are sleeping.

What is the best height for CO detectors? Are there current recommended heights or best practices to use when installing these things?

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    I do recall having instructions on more than one alarm that recommend NOT putting it within 6" of the ceiling (if on the wall) or the wall (if on a ceiling) to due possible "stagnant air in the corners." I'm surprised if the instructions on yours are really so vague that all they say is "can be either wall or ceiling mounted." – Ecnerwal May 21 '15 at 2:40
  • @Ecnerwal The instructions do have a bunch of guidelines for which rooms to place the alarm and how far away it must be from things like furnaces, stoves, windows, etc. However, it does not discuss the ideal height of the alarm, nor the avoidance of corners. I've edited the question with the model number and a link to the manufacturer instruction sheet. – Ben Miller - Reinstate Monica May 21 '15 at 3:34
  • For the Kidde digital display model we use, the manual says it can either be placed standalone on a table or at about eye level on the wall. CO tends to diffuse evenly with air, so there is no need to put them at a special height, as long as it's not in dead-air spaces like high up a vaulted ceiling. I tend to install them about 6 feet from the floor, high enough to prevent young children from touching the alarm while allowing adults to easily monitor and read the alarm. – bwDraco Jan 26 '17 at 21:09
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Carbon monoxide detectors should be installed according to the instructions that accompanied the unit.

From Nest Protect's website:

There’s a myth that all 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.

According to the carbon monoxide guidelines of the National Fire Protection Association (NFPA 720, 2005 edition), all carbon monoxide alarms “shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms,” and each alarm “shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit.”

Standalone carbon monoxide alarms are often placed low on the wall, but it’s not because they’re more effective at that height. It’s usually because they need to be plugged into an outlet near the floor or have a digital readout that can be easily read.

  • International Residential Code also points to NFPA 720, and the manufacturers installation instructions. – Tester101 May 21 '15 at 14:50
  • @Tester101 I tried finding a free version of NFPA 720, but it looked like all copies were $50. – Doresoom May 21 '15 at 15:15
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    Found this: NFPA 720 "9.4.1.2 Each alarm or detector shall be located on the wall, ceiling, or other location as specified in the manufacturer's published instructions that accompany the unit. and "9.7.1.1 All carbon monoxide alarms and detectors shall be installed in accordance with the manufacturer's published instructions. and "A.9.4.1.2 The location for effective performance is not generally dependent on mounting height. The density of carbon monoxide is similar to that of air at room temperature, and carbon monoxide generally mixes readily with air." – Tester101 May 21 '15 at 16:09
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I've been working as a service tech.for the last 20 yrs & in my opinion I would install it right under your thermostat, assuming that IT'S installed at the correct height which would be about 5 & a half ft.from the floor or about eye or face level, reason being is that carbon monoxide enters your blood stream by way of the air you breathe.If it's a plug in type (which is what I prefer) I would use the length of the cord as a guide line & avoid corners cause it's true that air in corners does get stagnant there due to friction. Keep in mind though, air is always moving because of 1 reason or another & it's not rocket science,it doesn't have to be perfect, close is good enough.

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