Proper Elevation of a Carbon Monoxide Detector

The myth that carbon monoxide rises in air

• There is a common misconception that carbon monoxide is significantly lighter than air, and thus rises. If this were true, it would be best to position a CO detector near the ceiling of a room, where the carbon monoxide would build up first. This idea, however, is incorrect.

  While it is true that carbon monoxide is lighter than the average weight of air, this difference is very small (CO is only 3 percent lighter than air and weighs the same as nitrogen gas, which makes up most of the atmosphere). Even if this difference were larger, however, lighter gases do not normally form a layer or float on top of heavier gases. Instead, air currents and the random movement of air molecules keep different gases well mixed. In addition, when carbon monoxide is created in a faulty furnace or oven, it is already well mixed with the other gases produced in the reaction, making it even less likely to separate itself.

  As a result, it is not important to position a carbon monoxide detector high on the walls or on the ceiling of a room.

Where to put the detector

• The most important part of deciding where to place a carbon monoxide detector is being sure that the family will be able to hear it, even if they are asleep. Thus, the detector should be located in, or right outside, a bedroom. If different bedrooms are in different parts of the house it may be best to acquire multiple detectors. Also, if you are seriously concerned, it may be best to position another detector in the furnace room, which will give the advantage of early detection.

  Because, in many cases, carbon monoxide will be warmer than the ambient air, it is unlikely to be found near the floor. The official government recommendation is therefore that the detector be positioned at about eye level. Different units may be designed differently, so consult your detector's instructions before positioning it.