Where you permanently mount a CO2 (carbon dioxide) monitor depends on why you are monitoring the gas.
In the case of home or office environments, a CO2 IAQ monitor should be placed at a height that best measures the typical indoor air.
Where to mount your CO2 IAQ Monitor?
The sensor mounting height of any gas detector depends on the type of application and on the density of the target gas relative to air.
When measuring heavier than air gases like carbon dioxide, the sensor should be near the floor. Sensors for lighter than air gases like nitrogen or helium should be placed near the ceiling.
To measure indoor air, a CO2 IAQ monitor should be mounted at the same height (60 inches or 152cm is standard) as you would mount a wall thermostat.
When it comes to indoor air quality applications, CO2 monitors should be placed in high traffic areas or environments that hold the most occupants.
It is always a good rule of thumb that CO2 IAQ monitors should not be placed near doors or windows that open to outdoor air as they will impact the normal composition of the indoor air. By the same token, they should be placed in areas where there is good air circulation, but not in the path of fans or rapidly moving air.
In addition, CO2 IAQ monitors should also be mounted upright on a vertical surface like a wall, column or beam and not mounted upside down or diagonally.
Why should I monitor CO2 levels for IAQ?
The principle behind CO2 monitoring is that it gives an indication of the ability of the HVAC system to exchange the air. High levels of CO2 indoors indicate poor ventilation and not enough fresh air coming into the space. Poor air circulation not only gives occupants the feeling of "stuffy air" but is positively correlated with high levels of dust, dander, mold, mildew, bacteria and viruses in the air.
In addition, studies show a direct correlation between high concentrations of CO2, employee productivity and health in office settings.
Home or Office Indoor Air Quality Monitors
In most homes or offices, wall-mounted CO2 level transmitters are used to monitor carbon dioxide levels as they would be experienced by occupants. They should be located at the same height (60 inches or 152cm is standard) and on the same wall as you would mount a thermostat.
Like a thermostat, they should not be near outside doors or windows that can make the space appear to have more fresh air than it actually does.
Commercial HVAC Control
As an alternative to wall mounting, commercial HVAC contractors use duct-mounted CO2 transmitters. By sampling the air from the return air ducts, they are assured of getting the most consistent average air quality for each zone in the building.
CO2 Level Measurement for IAQ
When it comes to monitoring indoor air quality in any space, we look to ASHRAE as a main reference in understanding how to read your CO2 IAQ monitor and understanding the recommended levels.
In summary, ASHRAE recommends that levels in your home be between, maintained at or below 1,000ppm in schools and 800ppm in offices and homes.
High CO2 levels can mean that ventilation is insufficient for the number of people present, which might also be causing other IAQ issues.
Carbon dioxide levels can also be affected by many different thing in an indoor air environment such as:
- Age of a building (designed without current ventilation needs in mind)
- Design of a building (built for one purpose, now used for another)
- Function of a space (may not have necessary air flow/windows)
- Size of the space (may not allow enough room for adequate occupants)
- Other sources of CO2 (smoking, stoves, furnaces, water heaters, pets)
- Design of a building (built for one purpose, but now used for another)
Also consider: CO2 sensors can tell you if the ventilation is okay, but dangerous indoor air pollutants can still be present even if CO2 levels are low.
It's important that if you have established that your CO2 levels are inadequate to not only ventilate the space but try and remove sources of indoor air pollutants when possible.