CO detector placement

Unknown

"Head to Bed" head standing up to bed lying down anywhere between.

The specific gravity of CO for inside temps is lighter than air (.96 as compared to air which is 1) so no need to worry about temperature as an issue. It does not start to get heavier than air until the temp gets below 40 degrees (F)

However because they are Combo Units (which I really do not like) the local AHJ may require them on the ceiling.

By the way a CO detector will alarm in a fire before the smoke alarm.

Why not get low level CO detectors which alarm at 9 PPM and that way you as the contractor get the call before a first responder before there is any danger. I can send you some literature on CO Experts unit. The only other low level detector is sold by Jim Davis's company but I believe you have to have attended Jim's classes to purchase.

Timco

I just bought new combo CO / smoke detectors for my rentals. They alarm at 30ppm CO. I check all my furnaces / boilers every year, so I am really just concerned about a major incident. Keep in mind, a CO detector is not mandatory, but I feel an obligation to install them. Question is, just how adverse is it to just install them on the ceilings rather than at face level? These are higher end rental units and it would look terrible to have them anywhere at face level. Second question is in a 4-plex with an upper & lower common hallway, should there be a detector on both levels? The boiler room is off the lower hallway.

Thanks, Tim

Derheatmeister

Rise and fall

Tim, as far as i understand CO can rise and fall depending on the Temperature.

So with that said i install CO detectors at bed sleeping level. And yes at each level.

Mark Eatherton

Richard's right...

Follow the manufacturers instructions. And don't worry about visual esthetics. You want these numbers to be "In your face" all the time.

ME

Buzz G.

CO

Gases such as CO and Nitrogen (&Oxygen and CO2) have weights based on their molecular wts.
CO=28, N2=28, O2=32, CO2=44
Thus the CO mixes with air which is 80% nitrogen fairly evenly and will not rise to the ceiling nor cling to the floor (CO2 goes down to the floor as it is heavier if there is no air movement to mix it in).
When heated, gases behave similarly and expand (ie get lighter) essentially the same amount(Boyles law describes the pressure-volume relationship). If the CO coming into an area is hot (like it is coming from a fire) it might then rise to the ceiling without mixing with the nitrogen-oxygen that is there already. In this case I would want my CO monitor high. It is unlikely that the CO leaked by a burner would be cold, but I can see a leak coming from a PVC pipe in a cold area as being colder. Of course then it would tend to accumulate in the basement or near the floor if the area is not in a basement.
I am not sure where you got the 40 degree info as it doesn't seem to fit the physical laws.

Timco

I ordered CO expert units for my own house, and the combo units for all my rentals. CO detectors are not mandatory, but I feel better having them. I do not have the cash to install a $200 detector in each of my rentals, especially when I am already going above & beyond the required. I also have smoke detectors on the ceilings inside & just outside of bedrooms where my housing inspector wanted them, and a 10# ABC extinguisher in each unit which is also not required.

Tim

Unknown

Buzz, I do not remember

were I got the 40 degree temperature. I do know from 50 years of dealing with CO in a combustion process that it does not always play by the rules.

I had an experience in a boiler room which was very cold (under 40 degrees) from two large air for combustion openings into the room with no CO at the ceiling in the room and 2500 PPM on the floor. Hence my theory is that as temp lowers it becomes more dense at least from a testing stand point. I have experienced this on numerous occasions in cold boiler rooms and garages with forklifts operating and contaminating the garage area.

I might also point out that because it mixes so easly with the air and CO2 we breathe it is not always hot when it gets into the living space. Yes in a flue sample it will be hot but not at the front door of someones house.

I am not a scientist just a humble service technician with hundreds of investigations concerning CO and when I recommend CO detector locations they are based on what I have found to be real world not necessarily always playing by the rules. As my good friend Mr. Jim Davis states this stuff never does what it is supposed to do so look out.

Jim Davis_3

I am pretty sure if your alarms our UL listed they are not allowed to go off at 30ppm for the first 30 days. They will go off at 70ppm in 1-4 hours and in 30 days at 69ppm.

CO is lighter than air until it gets to 32 degrees. It do not diffuse equally in a building at any time. It will always be higher at the ceiling than the floor. Because this is also a smoke detector, it should be mounted at a ceiling. Smoke is heavier than air and still lingers at the ceiling after the fire is out so I would say CO is going to be there also.

Buzz G.

Proper placement of a carbon monoxide detector is important. If you are installing only one carbon monoxide detector, the Consumer Product Safety Commission (CPSC) recommends it be located near the sleeping area, where it can wake you if you are asleep. Additional detectors on every level and in every bedroom of a home provides extra protection.

Homeowners should remember not to install carbon monoxide detectors directly above or beside fuel-burning appliances, as appliances may emit a small amount of carbon monoxide upon start-up. A detector should not be placed within fifteen feet of heating or cooking appliances or in or near very humid areas such as bathrooms.

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.

For this reason, the makers of First Alert (R), the leading brand in carbon monoxide detector technology, suggests mounting the detector on the ceiling. This also puts the detector out of the way of potential interference, such as pets or curious children.

The same discussion from a few years back is found at the:
http://www.newton.dep.anl.gov/askasci/chem03/chem03364.htm