Proper CO2 Sensor Location – Where To Mount Your NDIR Sensor


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Where to permanently mount your non-dispersive infrared (NDIR) sensor depends on why and where you are monitoring CO2 levels indoors, however, for best results they are usually placed 4-6 feet from the floor, also known as the “breathing zone”.

Carbon dioxide (CO2) is an inert gas, formed from respiration, combustion, and organic decomposition. As it is colorless it is impossible to detect with the human eye, therefore measuring CO2 levels with a CO2 meter is essential for human health and for a range of applications such as growth rooms. 

Non-dispersive infrared (NDIR) CO2 sensors are useful pieces of equipment to assess adequate ventilation in occupied zones. Measuring CO2 concentrations in spaces is used to indicate ventilation rates. This is vital in crowded spaces as indoor ventilation dilutes the amount of CO2 exhaled. 

The best place to mount your CO2 sensor is often a topic up for discussion. While some people will mount them on the ceiling, others will argue on placing them lower down because CO2 is heavier than oxygen (O2). 

Where To Mount Your CO2 Sensor

The mounting height of your sensor will depend on both the type of application being measured, why you are monitoring indoor air quality, and the density of the gas being measured, relative to air. Gases heavier than air should be detected 6 inches from the ground while gases lighter than air gases should be placed near the ceiling. 

Because CO2 has one carbon atom and two hydrogen atoms, its molecular weight of 44 g/mol means it has a higher density than oxygen, therefore CO2 is heavier than air. At standard temperature and pressure, the combined density of air is 1.29 kg/m3 compared to CO2 that has a density of 1.79 kg/m3. 

As CO2 is heavier than air, it will usually pool near the floor, and then fill the enclosed space, which is why it is recommended to place your NDIR sensor within the “breathing zone”, 4-6 feet from the floor. This is because a CO2 leak in a small room can become life-threatening very quickly. 

The “breathing zone” is an area where most human breathing occurs, making it a good location for CO2 sensors, as many gases will disperse in this area. 

When measuring indoor air quality in your home or office, the NDIR sensor is best located at the same height you would mount a thermostat on the wall. When placing your sensor, ensure it is not near any doors or windows that could interfere with the readings. 

Commercial HVAC contractors use duct-mounted CO2 sensors instead of mounting to walls. It is important to achieve consistent average air quality in different zones within buildings, which is why HVAC contractors sample the air from the return air ducts. 

For locations where compressed CO2 is stored, captured, or created, CO2 sensors should be mounted 16 inches from the floor because, as already mentioned, CO2 is heavier than air and can quickly fill enclosed spaces causing harm to human health. 

Things To Consider When Mounting Your NDIR Sensor

When you mount your sensor, avoid placing it near any ventilation fans, exhaust systems, or openings such as windows or doors that could interfere with the CO2 sensor. You should also place them near the source of gas where there is good air circulation, but not where they will be blasted by moving air. 

Accessibility to your NDIR sensor should be considered before placement, especially for sensors that require recalibration as you will need easy access. For example, if you place the sensor 25 feet above the ground, it will be very difficult to reach or even be a hazardous operation. 

Because many CO2 sensors use a NDIR gas detection cell to detect CO2 levels, these types of sensors should never be pointed directly at sunlight as they may give false readings. If you are using a CO2 sensor in a bright environment, you can try attaching a PVC Tee to the sensor to block any direct sunlight. 

CO2 sensors are also limited in:

  • Areas where only a few people occupy them, such as fitting rooms or large office spaces.
  • Large rooms with open spaces and high ceilings such as warehouses where air may not be fully mixed 

If you are ever unsure of the proper location for your CO2 sensor, speak to the manufacturer, as some applications may require sensors to be mounted at different heights than we have mentioned above.

CO2 Sensor Location For Grow Rooms

Too much CO2 in grow rooms can be a major issue, so by mounting an NDIR sensor you will be able to invest more time into growing and less time spent worrying about CO2 levels. 

When mounting NDIR sensors in grow rooms you must be aware of exhaust systems, injection points, air circulation, and the plants position. 

By using a CO2 meter in the grow room, you can be sure not to increase levels too high to cause human health concerns, and simultaneously monitor CO2 levels to ensure they stay in optimal photosynthesis ranges for the plants. Both of which are extremely important when tackling CO2 enrichment.


Where to mount your non-dispersive infrared (NDIR) sensor depends on why and where you are monitoring CO2 levels. In most cases they should be placed in the “breathing zone”, 4-6 feet from the floor because that is where the most mixing of gases occurs.
If you have any questions regarding CO2, NDIR sensors, or other testing kits used for gases, do not hesitate to contact our world-class team at Atlas Scientific.

CO2 Sensor & Scrubber

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