Carbon Monoxide Detector Placement

Real Estate Agent with Keller Williams Capital Properties DC AB15253

I love going back to my bookmarked posts and finding the oldies but goodies to find posts that we should all remember! this one by Jay Markanich gives us lots of information about carbon monoxide and the detectors.  Which one should you buy and where should you put it? Jay Markanich gives us all the answers!

Original content by Jay Markanich 3380-000723

Carbon monoxide detector placement.

That title surrounds a question I get a lot during home inspections.  And this one -

Is carbon monoxide lighter or heavier than air?

Of course, any time you have gas appliances or a wood-burning fireplace, you should have at least one carbon monoxide (CO) detector in the home.

CO is odorless, tasteless and DOES NOT GIVE WARNING that it is being produced or building up.

And, is it lighter or heavier than air?  Which means, does it rise or fall when produced?

Since the molecular weights of gases differ, what makes them move is convection.  If a gas is released because of combustion, it would tend to rise due to its heat.

CARBON MONOXIDE HAS NEARLY THE DENSITY OF AIR.  CO is slightly lighter.   You can figure this out.  For example:

O=16   C=12   N=14   H=2

You would add things to get the pure density of gasses.

H2 = 1+1 = 2 (very light)
O2 = 16+16 = 32 (slightly heavy)
N2 = 14+14 = 28 (about neutral)
CO2 = 12+16+16 = 44 (heavy)
CO = 12+16 = 28 (about neutral)
H2O = 1+1+16 = 18 (light) - as in humidity or steam
Radon = 222 (very heavy)

So what is the density of air?  The air we breathe is composed of 80% Nitrogen, 19% Oxygen, .6% inert gases and .4% Carbon Dioxide.

N2 + O2 + CO2 = ?
.8(28) + .196(32) + .004(44) = 28.9 (by definition air is neutral)


So how does CO compare with air?  It is 3% lighter.  So it distributes very easily through a house.


But when CO is produced, it immediately begins mixing, and therefore diluting, with the air around it.  Therefore, it mixes with nitrogen, which doesn't burn, oxygen, which is burned creating the CO, H2O (humidity) and CO2 which are in the air.  So the CO produced is not in pure form in the air.  It is very diluted.  And as CO is produced, it is warmer than the air around it.

So what is the most advantageous place to put a CO detector?  CO moves with the air, so where the air is flowing it will go also.  It is very unpredictable where the air, and therefore CO, will move at any given time.  That is why the instructions with the unit you buy do not say to place it high or low on the wall.

Understanding all that, the National Fire Protection Association (NFPA) suggests in 720, 2-1.1.2* 1998 -

"A carbon monoxide alarm or detector should be centrally located outside of each separated sleeping area in the immediate vicinity of the bedrooms. Where bedrooms are separated and the audibility of the alarm or detector to occupants within the bedroom area could be seriously impaired, more than one unit could be needed. Each alarm or detector should be located on the wall, ceiling, or other location as specified in the installation instructions that accompany the unit."


Which detector should you buy?

The suggestion is one that is plugged in and preferably with a battery back up.  These detectors use electrochemical technology to detect CO gas.  Like smoke detectors, they are effective for 10 years.

A local Fire Marshall, my neighbor, told me that the plug-in detectors seem to have a better record for fewer false positives than do the battery-only detectors.  But that is his experience!  

My recommendation:  buy a good plug-in detector!  If you want, get one with a battery back up.  Put it near any potential CO source and another near your bedroom(s).  Be sure everyone will hear it.


And you will be safe and feel safe. 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

Comments (12)

Wayne Martin
Wayne M Martin - Chicago, IL
Real Estate Broker - Retired

Good morning Lise. What a great choice for a reblog. Miss Jay's regular posts. He was/is a tremendous resoource of information. Enjoy your day.

Feb 25, 2021 05:29 AM
Michael J. Perry
KW Elite - Lancaster, PA
Lancaster, PA Relo Specialist

I actually need to get a new CO detector . I wasn’t satisfied with Night Hawk . It would go off if my dog passed gas close to it !!!!

Feb 25, 2021 05:30 AM
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Thank you Lise!  That is indeed an oldie, and perhaps a goodie, and on my website it has become very popular.  I deal with CO detector questions all the time.  It is a good topic to familiarize ourselves with!

Feb 25, 2021 05:48 AM
Ed Silva

Jay Markanich   Good to see hyour smiling face at least in a comment

Feb 25, 2021 06:34 AM
Rocky Dickerson
Realty One Group - Las Vegas, NV
Superior Service!

Good morning Lise Howe great information to repost. Thank you for bringing this to us.

Feb 25, 2021 05:49 AM
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Michael -- it may have been time to replace it.  They only last 10 years.  I have and like the Night Hawk, and it's considered a good one, but any one will probably do.

Feb 25, 2021 05:50 AM
Joan Cox
House to Home, Inc. - Denver Real Estate - 720-231-6373 - Denver, CO
Denver Real Estate - Selling One Home at a Time

Lise, great choice for a reblog, and haven't seen Jay in quite some time.  Great tips! 

Feb 25, 2021 05:56 AM
Ed Silva
Mapleridge Realty, CT 203-206-0754 - Waterbury, CT
Central CT Real Estate Broker Serving all equally

They have become big issues in our state and home appraisers need to make note of them for the banks

Feb 25, 2021 06:35 AM
Paul S. Henderson, REALTOR®, CRS
Fathom Realty Washington LLC - Tacoma, WA
South Puget Sound Washington Agent/Broker!

Thank you for sharing Mark's blog post with us. As a boater, we were taught that  the CO detector be placed low and we were shown people who died in their sleep because of the neutral state. Thank you Lise Howe 

Feb 25, 2021 08:41 AM
George Souto
George Souto NMLS #65149 FHA, CHFA, VA Mortgages - Middletown, CT
Your Connecticut Mortgage Expert

Lise this is good information to pass on.  Good choice for a re-blog.

Feb 25, 2021 01:03 PM
Endre Barath, Jr.
Berkshire Hathaway HomeServices - Beverly Hills, CA
Realtor - Los Angeles Home Sales 310.486.1002

Here in Los Angeles we have to have a Retrofit Inspections and a Certificate so we are good to go, good information just on a side note:)Endre

Feb 25, 2021 10:15 PM
James Dray
Fathom Realty - Bentonville, AR
Exceptional Agents, Outstanding Results

Morning Lise.

We have several inspectors in my are that does those tests routinely. 

Feb 26, 2021 12:19 AM
Brian England
Vacasa - Gilbert, AZ
MBA, GRI, REALTOR® Real Estate in East Valley AZ

This is a really good one to pull from the past.  At Vacasa, all of the properties we manage are required to have carbon monoxide detectors in them.

Feb 26, 2021 04:39 AM

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