# "Where Should I Put A Carbon Monoxide Detector?"

By
Home Inspector with Jay Markanich Real Estate Inspections, LLC 3380-000723

"Where should I put a carbon monoxide detector?"

That is 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 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, as to molecular weights:

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

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."

Again, the NFPA suggests 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).

And you will be safe and feel safe.

Posted by

Jay Markanich Real Estate Inspections, LLC

Based in Bristow, serving all of Northern Virginia.

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

www.jaymarinspect.com

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1. Brad Rachielles 03/28/2011 02:35 PM
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Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

It's hard to tell which position on the wall would make a difference Ginny!  Where's the air going?

Disallowed plug ins?  That's news...

Mar 17, 2011 11:28 PM #5
2,758,460
TeamCHI - Complete Home Inspections, Inc.
Complete Home Inspections, Inc. - Brentwood, TN
Home Inspectons - Nashville, TN area - 615.661.029

Interesting data for the general pop. It really doesn't matter where you place the detector...

Mar 17, 2011 11:28 PM #6
Rainmaker
533,824
Kenneth Cole
Weichert Realtors Appleseed Group, 2043 Richmond Ave. S.I.N.Y. 10314. office phone 718-698-9797, Appleseedhomes.com... - Staten Island, NY

Mar 17, 2011 11:40 PM #7
2,736,118
Lenn Harley
Lenn Harley, Homefinders.com, MD & VA Homes and Real Estate - Leesburg, VA
Real Estate Broker - Virginia & Maryland

Better yet, have an all eelectric home.

Mar 17, 2011 11:50 PM #8
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Just place'em!  Thanks Michael.

You're welcome Ken.  Glad you can use the information.

Gee, Lenn, where have I heard that before?  But people with all electric can still have a wood-burning fireplace!

Mar 17, 2011 11:55 PM #9
Rainer
171,030
Robert Butler
Aspect Inspection - Montreal West Island, QC
Montreal Home Inspector | Aspect Inspection

The important thing is to have one somewhere. I do get Lenn's answer from clients very commonly. (Because their regular heating is not based on combustable fuel).

They are forgetting vehicles in attached garages (remote starters), fireplaces (wood, gas, electric), candles and hurricane lamps, as well as FIRE.

Most house fires around here have electrical causes. They start inside walls and there is no smoke till it's too late. CO detectors can give you an early warning.

Mar 18, 2011 02:37 AM #10
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Mar 18, 2011 02:47 AM #11
Rainer
305,758
CENTURY 21 Peak, Ca BRE# 01489453 - Upland, CA
REALTOR, CDPE, Upland, CA

Jay, Thanks so much. Will reprint for my client and create a link to this from my outside blog. Just what I was hoping for.

Mar 18, 2011 07:28 AM #12
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

You are very welcome Brad.  Thanks for the off-line contact!

Mar 18, 2011 08:40 AM #13
Rainmaker
488,436
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Jay,

Great info on this and what is air chemistry. I know from emergency response/HazMat work that oxygen levels below 19.5 % are considered oxygen deficient. So combine that with how the blood metabolizes Carbon Monoxide it can get to a bad place quickly.

Mar 19, 2011 05:29 AM #14
Rainmaker
233,449
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Great discussion of the 'high and low' debate.  I was at a recent seminar where the HVAC guys were adament about CO alarms only being installed on the ceiling, but they said a bunch of other stuff that I didn't believe.  I'm with you; high or low is fine.

My two cents would be to follow the rules of a jurisdiction that has made CO alarms a requirement; here in Minnesota, they're required within 10' of every sleeping room.

By the way, where did you get the 10 year replacement rule from?  I always thought it was 5 years for CO alarms.

Mar 19, 2011 09:21 AM #15
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Thanks Donald.  I didn't know about that 19.5% thing.  I understand that 20.5% would be just as dangerous as there would be fires everywhere!

Reuben - if high and low was important the manufacturers would be the first to suggest a location.  Air moves, so where should my detector be?  Dunno!!  It's common sense.  The ceiling would be good near a return moving air over the detector!

The 10 year things depends on the manufacturer.  I did read some info that said certain ones are on the 5 year plan.  And the NFPA suggests replacement every 10.

Mar 19, 2011 12:12 PM #16
Rainmaker
644,115
DeeDee Riley
Lyon Real Estate - El Dorado Hills CA - El Dorado Hills, CA
Realtor - El Dorado Hills & the Surrounding Areas

Great information to know, Jay!!!

Mar 19, 2011 06:03 PM #17
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

This one was fun to research and write about DeeDee.  Glad you enjoyed it!

Mar 19, 2011 09:42 PM #18
Rainmaker
579,627
Chris Smith
Re/Max Chay Realty Inc., Brokerage - New Tecumseth, ON
South Simcoe, Caledon, King, Orangeville Real Esta

Great information Jay, It is still not common knowledge that both smoke detectors and carbon monoxide detectors need to be replaced.

Mar 22, 2011 08:28 AM #19
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

I hear you Chris.  And it really is important.  Hence the news line at the end of the post.

Mar 22, 2011 01:37 PM #20
1,620,314
Alan May
Coldwell Banker Residential - Evanston, IL
Helping you find your way home.

That is interesting.  I'd always been told that CO was heavier than air... that's why my inspectors have told me to place them low on the wall.

But your information is pretty compelling.

Apr 07, 2017 03:59 PM #21
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

It's basic periodic chart stuff, Alan.  I simply tell my clients to put one near the source and one near the bedrooms.

Until, that is, the nannies jump down my throat too and want one near every bedroom!

I did recently finish a basement bedroom (by my lonesome and hey, the county approved everything!) which is not too near to the source of CO in my furnace room, so I did put a detector outside that one!  There's one in the basement furnace room too.  It's simple to do and cheap.

Apr 08, 2017 02:28 AM #22
Rainmaker
513,332
Elva Branson-Lee
Solid Source Realty GA - Atlanta, GA
CDPE - Atlanta Real Estate & Short Sale Agent

Jay, this is useful information and a great discussion. Thanks for shairng it.

Apr 08, 2017 05:34 AM #23
Rainmaker
1,834,054
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

You found an oldie but a goodie, Elva!  Twice in two days people have comments on such an old post!

I'm glad you found the information useful!

Apr 08, 2017 12:48 PM #24

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Rainmaker
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Home Inspector - servicing all Northern Virginia
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