All our gas safety alarms have sensors that measure specific gas levels in the air. Because some gases are heavier than air they will tend to “pool” at different heights in an enclosed area. Therefore, when mounting a gas safety alarm you should to mount the sensor at a height closest to where the gas will be sensed first. You can do this by knowing the weight of your target gas relative to the air in the room.
The chart below lists the molecular weights of various gases. Note that the molecular weight of fresh air is approximately 28.9. Gases with higher molecular weights will tend to rise in an enclosed area or room, whereas gases below will tend to sink toward the floor.
When deciding where to mount a gas safety alarm sensor, find the gas you are monitoring on the list, then note whether it is heavier or lighter than air. This will tell you where to mount the sensor.
For example, an oxygen sensor should be mounted higher on the wall while a carbon dioxide sensor should be mounted near the floor.
While this chart should be used as a general guideline, when using any gas safety monitor always check the manufacturer's instructions first before mounting the sensor.
Common Fixed Gas Sensor Mounting Heights
Carbon Dioxide Sensor Mounting Height
CO2 is heavier than air. Therefore, fixed CO2 safety monitor sensors should be mounted approximately 12 inches (30 cm) off the floor.
Carbon Monoxide Sensor Mounting Height
CO gas is approximately the same weight as air. However, it also rises with warm air. Therefore, the United States Environmental Protection Agency (EPA) recommends placing a carbon monoxide detector on a wall about 5 ft. above the floor or at eye level. The EPA also recommends at least one CO monitor in every bedroom and at least one on every floor of a building, including the basement.
Propane or LP Sensor Mounting Height
Propane is heavier than air. Therefore, fixed propane safety sensors should be mounted 4-6 inches (10-15 cm) off the floor. In addition, the sensor should be placed as close to the source of a potential leak as possible.
Oxygen Sensor Mounting Height
Oxygen deficiency alarms report the lack of oxygen by volume as it is displaced by another gas. Therefore, if the gas of concern is heavier than air (for example, CO2 or chlorine), the oxygen sensor should be mounted close to the floor. If several gases are being monitored, the oxygen sensor should be mounted at least 6 ft. above the floor, as we want to measure the oxygen before someone could become asphyxiated.
Refrigerant Sensor Mounting Height
Refrigerant gases like hydrofluorocarbons (HFCs) are much heavier than air, so the refrigerant sensor should be mounted 4-6 inches (10-15 cm) off the floor. However, it is equally important if possible to place the sensor as close to the source of a potential leak, but not near a fan or other source of moving air.