CO2 Sensors vs. VOC Sensors for IAQ - What's the Difference?

Indoor Air Quality CO2 Sensors vs. VOC

Customers often ask about the differences between VOC (Volatile Organic Compound) sensors and CO2 (Carbon Dioxide) sensors. While both can be used to measure indoor air quality (IAQ), these sensors are not interchangeable.

They measure very different things.

While many customers are often searching to measure the lack of fresh air in the room, the question becomes how to monitor and maintain a comfortable indoor environment - and better yet, which sensor to choose from?

Why measure VOCs?

The EPA most commonly classifies a volatile organic compound (VOC's), as "any compound of carbon that participates in atmospheric photochemical reactions". This classification also eliminates carbon monoxide, carbon dioxide, carbonates, ammonium and more. Leaving VOC's as the main substance that is realized in the air from hazardous chemicals that vapors. These chemicals can directly and negatively impact your health, well-being, and productivity. Thus, the need for monitoring VOC's can be very critical.

Since VOC's can be a leading cause of severe health effects both short and long term, individuals should utilize sensing technologies in order to reduce the amount of VOC's in indoor air environments. VOC's can cause effects such as eye and throat irritation, liver and kidney damage, cancer or severe ailments depending upon the amount of exposure. 

Common VOC's stem from a variety of household products such as paints, cosmetics, scented candles, fragrances, new furniture, cleaning products, cooking sprays and even children's toys. Because these products are used in indoor air environments like homes, offices, or classrooms these VOC gases can tend to build up in the air and contaminate any fresh air. 

In order to combat the spread of VOC's in your indoor air environment, many customers resort to regularly replacing air filters, avoiding purchasing products with high VOC's, utilizing used furniture, or reducing the amount of products that contain them. However, even these small acts towards reducing the gases can not always be enough. Hence, the creation of VOC sensor technologies.

Volatile Organic Compound Sensors

Many VOC sensor technologies are commonly used across indoor air environments to evaluate the air quality and monitor the microscopic particles that human senses can not detect.

VOC sensors such as the IAQ-2000 or IAQ-0001 can specifically measure the concentration of these particles, identifying when concentrations get too high and furthermore providing notification when increased ventilation is needed.

This sensor shown above specifically is a sensitive, low-cost solution for detecting poor air quality due to the micro machined metal oxide semiconductor (MOS) technology that is able to detect a broad range of VOC's while correlating directly with CO2 levels in the room. 

Note that VOC sensors are designed to provide a total VOC concentration not the specific element/compounds.

Unlike a CO2 sensor, however, a VOC sensor cannot indicate the specific rate of ventilation needed, only the level of VOC's in the air. It can however indicate a general change in the concentration of contaminants.

In the case of VOC sensors, ventilation is regulated based on the actual presence of some pollutants sensed by the air quality sensor. This may or may not conflict with established ventilation codes. These sensors can also be used to sense periodic episodes of high pollution that might occur when special equipment is being used, or when potent chemicals from cleaners are released into the air.

VOC's that can be detected by using a sensor such as the IAQ-2000 include:

  • CO, CH4, LPG
  • Alcohols
  • Ketones
  • Organic acids
  • Amines
  • Aliphatic hydrocarbons
  • Aromatic hydrocarbons

In addition, many customers may tend to lean towards a VOC sensor in indoor air quality environments due the energy saving aspect that can be established once a VOC sensor is integrated. When utilizing a VOC sensor, when the levels for targeted concentrations are exceeded, the module can alert a climate control system and increase ventilation. When VOC levels are minimized, the module can further instruct the system to decrease ventilation, thereby saving energy and lowering building operating costs. 

Why measure Carbon Dioxide (CO2)?

For many, carbon dioxide (CO2) has often been the "go-to" as it pertains to measuring indoor air quality across homes, classrooms, or commercial buildings. The sensor technologies are stable, they are not subject to short term drift, and most technologies provide a clear means to easily measure concentrations. In monitoring carbon dioxide (CO2) in indoor air quality environments you can gain a clear indication of how many occupants are in an enclosed space and gain understanding of the direct indication of contaminants that accompany human presence. 

Typically, when an individual is monitoring carbon dioxide, a CO2 level of 1,000ppm or greater is known to directly affect cognitive ability, ailments, asthma, productivity and even the ability to make strategic decisions. Aside from just the minor health effects, those CO2 concentrations that range higher around 30,000ppm - 70,000ppm can even be life-threatening.

Carbon Dioxide CO2 Sensor for Indoor Air Quality


Thus, the alternative for monitoring air quality of VOC, is measuring the CO2 levels, so you can maximize your understanding of how much ventilation in an indoor space is needed and capture substances that are emitted completely naturally from us humans - such as respiration.

A CO2 sensor like our most popular, K30 10,000ppm CO2 Sensor is designed to control the ventilation rate in occupied spaces. Since people are the principal source of CO2 in indoor air, an indoor CO2 measurement can be used to determine whether a room or building is occupied. In other words, higher levels of CO2 correspond to larger numbers of people inside, and therefore, the rate of air exchange required.

As a control, a CO2 sensor can also activate an alarm or mitigation strategy (activate filters or ventilation). Because carbon dioxide is an inert gas, it is one of the few elements that will not cause an air quality sensor to react. Both approaches can be applied to a demand-controlled ventilation strategy, but the results may be very different.

When you use CO2 sensing, energy savings also can result because ventilation is based on actual occupancy of the space rather than the design occupancy of the space. Energy is saved when pollutant loads are low and ventilation can be reduced, which may occur during or after occupied hours. Where a CO2 sensor would specifically reduce ventilation during unoccupied periods, a VOC sensor may actually maintain ventilation rates during unoccupied periods if there is a significant pollutant level in the building.

Carbon Dioxide (CO2) Sensors

In identifying the real comparison between CO2 sensors vs. VOC sensors, it is known that CO2 often will remain the "go-to" guide for monitoring indoor air quality environments. This is due to the fact that CO2 is much more easily captured and easy to measure, giving a constant indication to the end user.

A CO2 sensor will also automatically indicate whether an indoor air environment holds a CO2 content of 1,000ppm (parts-per-million) or greater, which is determined as "poor indoor air quality". Too high of CO2 concentration will directly affect cognitive abilities, decision making, productivity, and even lead to severe ailments. Higher levels ranging from 20,000ppm - 70,000ppm can even be life-threatening.

Because CO2 sensors are often an alternative measure for VOC sensing, it is important to recognize that a key difference is in the contaminants being captured. While VOC's can provide indication of specific particulate matter from household items, it can not show specific value the same way a CO2 sensor can. While CO2 sensors can indicate a set value in ppm measurements, it provides a clear and easy to understand value of good vs. bad air quality. Additionally, VOC sensors are also needing to be constantly calibrated in order to pinpoint the precise particulate matter contaminates, making the technology more difficult to use on a day-to-day basis. However, if you are utilizing a VOC sensor for a more modern demand-controlled ventilation application; these levels could be converted to CO2 values. 

    Overall, the real delineation between CO2 vs. VOC sensors comes down to answering the following questions:

    • What are you looking to measure?
    • Are you needing to regulate what you are measuring?
    • How would you like this data to be shown?

    For more information on  indoor air quality solutions, contact us today.

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