Placement of Carbon Monoxide Detector

Where is the best place to place a CO2 detector? I know you should have them in bedrooms and main areas, but where on the wall or ceiling? Is the gas going to lay close to the floor or will it rise with the heat? Just wondering.

I installed a carbon monoxide only detector and the instructions said to keep it low on the wall, something like eye level or below because they said co is a bit heavier and tends to build up from the bottom. I installed a combination co and natural gas and propane detector made by the same company and the instructions said mount high for natural gas because it is lighter than air, and mount low for propane because it is heavier than air. These instructions claimed the co mixes evenly enough with the air at all levels that it will be detected. This somewhat contradicts their instructions they give for their co only detectors.

For me if it is battery powered I put it on the wall at a convenient height and location and the plug in type get plugged directly into an outlet.

Carbon Monoxide (CO) is lighter than air. But understanding where to mount a CO detector is not simple. Carbon Dioxide (CO2) and Oxygen (O2) are products of complete combustion under ideal conditions. CO is produced when there is incomplete combustion. If all 3 gases are spilled into an area the CO2 will drop to the floor and the lighter CO will rise to the ceiling. Air contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, plus trace amounts of other gases. However what you actual have at any point in your home is a mix of gases, greatly influenced by air currents created by natural drafts and the fact that heated air rises.

The molecular weight (grams/mole) of the gases we are talking about are:

Carbon Monoxide ------ 28.01 Lighter

Nitrogen ------------- 28.0134

Air ------------------ 28.964

Oxygen --------------- 32.00

Carbon Dioxide ------- 44.01 Heavier

Since the molecular weights are all very similar the gases mix easily. So, if I want to measure long term accumulation of CO you want the detector up high because it's the lightest gas. Eventually any CO in no gas movement environment would have the lighter CO rise to the ceiling on the highest floor. This is why measurements of background CO in homes show higher levels in the second floors. But, what you really want to measure is production of CO by your coal appliance. If it's producing CO you want to know it immediately. So put your first CO detector near your coal appliance slightly higher that where you think the CO might be coming out of your stove, i.e. stovepipe, feed door, etc. Your second CO detector should be on a wall near the ceiling, 6 to 12 inches down from where the wall meets the ceiling or on the ceiling. This detector will measure accumulated CO from all sources in your home if it is in the highest room in your house.

Both detectors should have digital readouts. Get out immediately if you see a reading of 35 ppm or greater. This is a lower number than the alarm set point. See my other post on CO safety warning.

I was bored lol, I stumbled upon this about CO being lighter than air and the placement relation of a detector

https://www.ncbi.nlm.nih.gov/pubmed/21536403

Even with petroleum based vapors -

But the petrol fumes would not stay for very long at ground level. Convection current carry them upwards, and gaseous diffusion would cause mixing with air even without convection. That's because gas molecules are in a state of constant motion, colliding with other molecules, millions of times a second, causing them gradually to diffuse ("spread") in all directions. The fumes gradually spread into all the space available - which could be a jar, a garage, a hangar, the entire atmosphere. Once the space is evenly occupied, the molecules then show no tendency to unmix. Why not? Answer: because the 1g force that acts on all molecules in air at sea level is insufficient to overcome the kinetic forces due to collision between molecules. Put more simply - a molecule that gets a strong bump from below will be knocked upwards, against the weaker force of gravity.

C/O detectors should be placed one (1) on every level of the home including the basement, but not in attics. They should be placed in hallways outside of bedrooms. Smoke detectors should be placed in every bedroom and one (1) on each level of the home including the basement. The smoke/CO detectors can be combinations, but they should be the "talking" type that tells you which alarm is going off, C/O or smoke. They should also have 10 year lithium batteries, if possible. The smoke/C/O in the basement should be located at the bottom of the basement stairs on the ceiling. The smoke/CO detector outside the bedrooms on the 1st & 2nd floors of the home should be located in the middle of the ceilings in the halls outside the bedrooms. The smoke detectors in the bedrooms should be located near the entrance doors to the room, 12" or more away from the wall or if mounted on the wall, 12" below the ceiling. The smoke detectors should also be the "photoelectric" type, not the "ionization" type that can give false alerts due to steam, cooking, etc. With the "ionization" type, people take the batteries out and you then have a non-functioning detector, not good!