Carbon monoxide (CO) is a colorless, odorless, and tasteless gas produced by incomplete combustion. This invisible chemical compound poses a significant, life-threatening risk within homes and enclosed spaces. Because CO is imperceptible to human senses, understanding its behavior is fundamental to implementing effective safety measures. The question of whether CO floats or sinks is directly related to the proper placement of detection devices necessary for protecting occupants.
Understanding Carbon Monoxide’s Density
The question of whether carbon monoxide floats or sinks can be answered by comparing its molecular weight to that of ordinary air. Carbon monoxide molecules have a molecular weight of approximately 28.01 atomic mass units (AMUs). In comparison, the average molecular weight of the air we breathe is roughly 28.97 AMUs. Since the molecular weight of carbon monoxide is slightly lower than air, it is technically less dense.
This minimal difference in density means that, in a perfect, still environment, carbon monoxide would rise slightly. However, in a real-world indoor environment, gases do not remain perfectly separate or stratified. The natural movement of air, known as convection, along with temperature gradients, causes the carbon monoxide to mix almost entirely and uniformly throughout the available space. Because of this thorough mixing, CO does not strongly float near the ceiling or heavily settle near the floor.
The takeaway from this physical property is that dangerous concentrations of carbon monoxide can be found at any height within a room. While the gas may initially be warmer and lighter when produced by a combustion source, it quickly cools and disperses. This rapid and even distribution is why the placement of a CO detector is more dependent on the location within the home than the specific height off the floor.
Optimal Placement of CO Detectors
Given that carbon monoxide mixes evenly with the air, the strategic placement of detectors is the most important factor for early warning. Safety guidelines recommend installing detectors on every level of the home, including the basement. It is especially important to place them near or inside sleeping areas, as this ensures occupants can be awakened if levels rise while they are asleep.
The general consensus for mounting height is often based on convenience and visibility rather than density physics. Many manufacturers recommend mounting detectors on a wall at chest height or higher, typically about five feet from the floor. This height keeps the device out of the reach of children and pets while making the controls and digital display easy to access and read.
It is also important to maintain a certain distance from combustion appliances to prevent false alarms, usually between five and twenty feet away. Placing a detector too close to a furnace, water heater, or fireplace may trigger an alert from trace amounts of CO that are safely vented. Conversely, placing the device too far away, such as near a window, door, or ventilation fan, may interfere with accurate gas detection due to drafts.
Common Sources and Prevention Strategies
Carbon monoxide is produced anytime a carbon-based fuel is burned without sufficient oxygen, leading to incomplete combustion. The most common household sources include gas-fired furnaces, water heaters, and clothes dryers. Other significant sources are gas stoves, ovens, fireplaces, and combustion engines, such as a vehicle running in an attached garage.
Prevention begins with ensuring all fuel-burning appliances are properly installed and maintained. A qualified technician should inspect and service your heating system, chimney, and all other fuel-burning equipment annually. This regular inspection helps identify cracks in heat exchangers or blockages in vents that could allow CO to leak into the living space.
Never use devices intended for outdoor use inside your home, garage, or any enclosed area. This includes portable generators, charcoal grills, and camp stoves, all of which produce high levels of carbon monoxide. Never leave a vehicle running in an attached garage, even with the garage door open, as the gas can easily seep into the home through shared walls and doorways.