Carbon Monoxide Detector Question

*I see most of them installed *in the hallway above the height
of the door frame…

I had a realtor tell me that this is incorrect because of the
weight of carbon monoxide. ( its heavier than air ).

Anybody got some scientific facts on this issue?




They should always be installed to the manufacturers instructions.

Some are ceiling mounted, some are 12 inches below the ceiling on the wall mounted.

They also have a five year expiration, so most all I see are due to be replaced, and I instruct my clients to install properly, or, pruchase the units for their preference of mounting locations.

According to the 2005 edition of the carbon monoxide guidelines, NFPA 720, published by the National Fire Protection Association, sections and, all CO detectors ‘shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms,’ and each detector ‘shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit.’

For the whole article.

Watch out for the “location” rule. Check with your State or Local. Centrally located would not fly in MN. Minnesota requires that it be installed “within 10 feet of any area legally used for sleeping”. Think about that one. It does not limit to bedrooms. Technically, a room with a ‘Daybed’ or ‘Sleeper/Sofa’ could qualify. Depending on the floorplan, a typical 4 bedroom home could require 3 detectors for coverage.

And some are designed to be plugged into a wall outlet (12 to 18" off the floor).

I just replaced all my smoke and CO detectors. I got them at home depot and read 3 different CO detectors that had different placement instructions.
Then you have the smoke and CO detector all in one. Where should that one be installed? :shock: :wink:

The most important thing to know about carbon monoxide detectors is that they are all insufficient and that people who have them can still be continuously exposed to dangerous levels of carbon monoxide without having their perfectly working CO detectors sound any alarm, no matter where they are placed.

I assumed that was a given for a ‘plug-in’ type, although there are always exceptions, such as an outlet installed at a custom height. Are they allowed to be installed at 78 inches??? :wink:

Anyone have a narrative to share. I did not give any thought to their design life until mentioned above.

James has a good point. I’ve tested elevated CO levels right in front of the CO detector. The detector didn’t alarm till 100ppm. They all alarm differently. It all varies by manufacture.

They are still better then nothing at all.

My narrative on them is this:
Recommend the installation of carbon monoxide detectors. Carbon Monoxide detectors should be installed to the manufactures specifications and within 15 feet of any slepping room. The detectors generally have a life span of five years so it may be in your best interest to take the expiration date sticker off the inside of the detector and install it on the exterior surface as a reminder.

Some used to be set at 50 ppm but like Robert points out others are set at 100 ppm.
Point being is low levels can still kill you as James is pointing out.

Got any written proof of that statement?
Would like to go along with you on that but “heresay” is not good enough.

Below copied from:


This section appears to contradict itself about the number of sensors available. Please see the talk page for more information. (March 2012)
Early designs were basically a white pad which would fade to a brownish or blackish color if carbon monoxide was present. Such chemical detectors were cheap and were widely available, but only give a visual warning of a problem. As carbon monoxide related deaths increased during the 1990s, audible alarms became standard.
The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations (e.g. 100 parts per million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarette smoke.*

Carbon monoxide is a colorless, odorless gas. It is a by-product of incomplete combustion from fuel burning appliances such as a furnace, water heater or fireplace. The symptoms of long term exposure to low concentrations include slight headaches, fatigue and shortness of breath with only moderate exertion. Continued exposure or high concentrations can result in severe headaches, breathing difficulties, dizziness, confusion, cardiac trauma, brain damage and ultimately, death. To help reduce the risk of exposure to carbon monoxide, fuel burning appliances should be inspected annually by a qualified technician. Recommend that Carbon monoxide detectors be installed near sleeping areas, they can also be installed on or near the ceiling in each room where there is a fuel burning appliance. Much like smoke detectors, carbon monoxide detectors can be wired directly into the homes electrical system, plugged into a receptacle and/or battery operated. Also, like smoke detectors, battery operated units should be tested weekly while hard wired systems should be tested monthly. If a CO detector does go off, immediately evacuate everyone from the home and call the fire department, open doors and windows to ventilate the house. Remember that because carbon monoxide is colorless and odorless, never ignore an alarm even if you feel no adverse symptoms. More information can be found in the CMHC document at
From the United States EPA (Environmental Protection Agency): Carbon Monoxide Detectors are widely available in stores and you may want to consider buying one as a back-up, BUT NOT AS A REPLACEMENT for proper use and maintenance of your fuel-burning appliances. However, it is important for you to know that the technology of CO detectors is still developing, that there are several types on the market, and that they are not generally considered to be as reliable as the smoke detectors found in homes today. Some CO detectors have been laboratory-tested, and their performance varied. Some performed well, others failed to alarm even at very high CO levels, and still others alarmed even at very low levels that did not pose any immediate health risk. Unlike a smoke detector, where you can easily confirm the cause of the alarm, CO is invisible and odorless, so its harder to tell if an alarm is false or a real emergency. Don’t let buying a CO detector lull you into a false sense of security. Preventing CO from becoming a problem in your home is better than relying on an alarm.

When considering where to place a carbon monoxide detector, keep in mind that although carbon monoxide is roughly the** same weight as air** (carbon monoxide’s specific gravity is 0.9657, as stated by the EPA; the National Resource Council lists the specific gravity of air as one), it may be contained in warm air coming from combustion appliances such as home heating equipment. If this is the case, carbon monoxide will rise with the warmer air.

I’ve been in a utility room where the furnace back drafted badly under worst case conditions. The room shot up to over 300 ppm within seconds. I can tell you that just that short exposure made me feel like crap for the rest of the day. I couldn’t imagine having a detector that didn’t go off till 400 ppm. Get the most sensitive one you can. I do like to have one in the home that has an actual reading on it.

I will say the the KIDDE gas one in the hallway outlet is the most sensitive I have seen. Believe it or not it can sense a very big dump of s h i t in your bathroom. I laughed so hard I could barely keep my composure it sensed the gas coming out of my butt. I believe it also is set at 50 ppm for CO.