Carbon Monoxide Detector Placement

Reblogger Sally K. & David L. Hanson
Real Estate Agent with EXP Realty 414-525-0563 57026-90 Broker

The state of Wisconsin requires smoke AND co2 detectors on  every level of a home. Whether your state requires it or not...doing it can be a life saving investment you will never regret. Don't put it it may be saving the life of a loved one or your own life as well.

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


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Nina Hollander
Coldwell Banker Residential Brokerage - Charlotte, NC
Your Charlotte/Ballantyne/Waxhaw/Fort Mill Realtor

Hi Sally and David... great choice for a reblog... carbon monoxide detectors beecame the law here in Charlotte some years back and no doubt that they can save lives.

Oct 09, 2018 01:00 AM #1
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Thanks for the reblog guys.  I did not know having detectors was law in so many states!  Replacing smoke detectors every 10 years is actually code but I find them to be too old in probably 80% of houses.  I expect it's the same with CO detectors.


Oct 09, 2018 03:15 AM #2
Roy Kelley
Realty Group Referrals - Gaithersburg, MD

Thank you very much for sharing this excellent reblog selection.

Oct 11, 2018 05:25 AM #3
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Sally K. & David L. Hanson

WI Realtors - Luxury - Divorce
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