Carbon Dioxide Monitors - How to Pick the Right CO2 Monitor

Carbon Dioxide Monitors - How to Pick the Right CO2 Monitor

When we talk about indoor air pollution, the topic of discussion more than likely revolves around particulate pollution such as PM2.5 or other common indoor pollutants such as volatile organic compounds or even mould. However, one pollutant we rarely consider, especially in the context of indoor air pollution, is carbon dioxide. 


Perhaps because we are constantly inhaling and exhaling CO2 throughout the day or because we always discuss CO2 in the context of outdoor air pollution, we rarely address indoor CO2 and its impacts. 


A few months ago, we wrote an article detailing why carbon dioxide is an indoor air pollutant you should be aware of. That article dives deeper into how carbon dioxide can impact our health and well-being and briefly touches on ways we can avoid the worst impacts of CO2.


However, while we fleetingly mentioned carbon dioxide monitors in that article, we didn’t delve into the important details you need to know to pick the right device. So today, we want to remedy that by deeply diving into carbon dioxide monitors.


Whether you’re still on the fence about whether or not you need a carbon dioxide monitor or have already made your decision but don’t know what to look out for, this post will cover all the essentials. So with that said, let’s dive right in!

What Does a Carbon Dioxide Monitor Monitor?

This might seem like a very straightforward question - after all, a carbon dioxide monitor simply monitors carbon dioxide, right? Yes! But there are a few implications when it comes to monitoring CO2. Let’s discuss the three main reasons people purchase these devices:

1. Carbon Dioxide

Starting with the obvious, a carbon dioxide monitor's core purpose is to monitor carbon dioxide concentrations. These concentrations are worth monitoring because high levels can significantly impact your health and well-being. For example, even at relatively low concentrations, carbon dioxide can reduce our cognitive function by 50%!


On top of reducing our cognitive function, higher concentrations of carbon dioxide can lead to drowsiness, reduce the quality of our sleep, and, at more extreme levels, cause headaches. For all of these reasons and more, carbon dioxide is worth keeping an eye on and a CO2 monitor will allow you to do so.

2. Ventilation

The second reason many people purchase carbon dioxide monitors is that they can be used to identify ventilation in indoor environments. Since ambient air has a CO2 ppm (parts per million) concentration of around 420, we can set this as a baseline for well-circulated air. However, as the CO2 concentration climbs, less fresh air is circulated.


This allows us to identify when air is stagnant and when the air might be impacting our mental and physical health. While the carbon dioxide concentration isn’t a perfect method for measuring ventilation, it’s the best we currently have.

3. Airborne illness transmission risk

Most interestingly, carbon dioxide monitors also allow us to gather information on the transmission risk of illnesses, albeit indirectly. This is the reason behind the current trend in CO2 monitors - they can be used to predict COVID-19 transmission chances with a few caveats.


Since viruses and illnesses are more transmissible in environments with little or no ventilation, we can assess the danger of airborne diseases by understanding the ventilation in a room or building. Of course, with a carbon dioxide monitor, we can understand ventilation and, therefore, as a proxy, viral transmission chance.


Of course, there are caveats to this. For one, a high carbon dioxide concentration doesn’t relate to COVID-19 transmission chance unless an infected individual is present. Many other factors can impact transmission chance, making carbon dioxide concentrations a less-than-perfect method for monitoring transmission chance.


With that said, with no way to monitor viral particles directly, carbon dioxide monitors give us the best method to identify airborne illness transmission risk.

4. Other environmental factors

I've included this as an extra point because it's not a key reason people buy a CO2 monitor. After all, buying such a monitor just to keep an eye on the temperature or humidity is a rather costly approach.


However, carbon dioxide monitors tend to come with a few other sensors too. In nearly every case, you'll find that temperature and humidity sensors are included alongside the CO2 sensor. While there's no reason to buy a CO2 monitor just for these sensors, they are a handy addition and can provide more accurate insights into your indoor air quality.


Some carbon dioxide monitors will also feature sensors to keep track of other pollutants such as PM2.5 or VOCs. These products tend to be a bit more expensive, though, and have shorter battery life due to the increased power draw.


Do You Need a CO2 Monitor?

A CO2 monitor allows us to know in which environments masking is necessary and which are best avoided.


That brings us to the next important question: do you need a CO2 monitor? Again, this will come down to your priorities and how actively you want to be able to keep an eye on carbon dioxide and ventilation levels.


In itself, a carbon dioxide monitor is not a tool to solve any problems. Having a carbon dioxide monitor won't be an instant fix to poor ventilation, and, in fact, it won't be a fix at all. A carbon dioxide monitor's only purpose is to provide insights into CO2 and, as a proxy, ventilation levels and viral transmission risk.


However, it's up to you to take further actions to offset these issues based on what the monitor says. More often than not, these actions are simple such as opening a window or turning on outdoor air circulation in the car - both actions that can be taken without a monitor.


At this point, it might seem like we are recommending against getting a CO2 monitor. That's not true, but CO2 monitors are only one step in creating better indoor air. Furthermore, if a CO2 monitor is out of your budget, there's no reason you can't still take steps toward improving your air quality.


With that said, what will a CO2 monitor allow you to do? Well, most obviously, it will enable you to analyse carbon dioxide concentrations accurately. There is no more guesswork in figuring out CO2 levels with a carbon dioxide monitor.


Perhaps most usefully, carbon dioxide monitors allow you to quickly and easily analyse what works and what doesn't. For example, it's only sometimes a given that simply opening a window will bring the CO2 concentration to a reasonable level. With a monitor, you can know exactly what is working and what isn't.


Further, CO2 monitors have a helpful purpose as risk analysers. While we have already discussed some of the flaws regarding using these devices for measuring transmission risk, they are the best tools we currently have.


With a portable monitor, you can quickly judge risk in different environments. For example, if a cafe or restaurant is busy and has a reading of 2500 ppm, it could be well worth avoiding due to the relatively high risk of airborne illness transmission.


With the health impacts of Long COVID still being researched and more health implications being discovered daily, this feature is incredibly useful. Not only can you judge when a mask is needed, but you can also judge whether some venues should be avoided altogether. 


So, do you need a carbon dioxide monitor at the end of the day? Many people won't, but anyone wanting to take control of their air and to be able to analyse ventilation and transmission risk effectively should consider purchasing one of these incredibly useful tools.


How to Choose the Right Carbon Dioxide Monitor

Aranet4 and Vitalight Mini CO2 Detector. Image from BreatheSafeAir.


With the increasing popularity of carbon dioxide monitors due to their double purpose as a COVID transmission risk monitor, the market now has a wide range of devices with different features and prices.


But how do you pick the most suitable device? It can be a tough choice, so we'll discuss some of the most critical factors you'll need to consider when choosing the right device for your purposes. 

Battery life


Depending on how you plan to use your carbon dioxide monitor, battery life can be a deciding factor when choosing between two or more devices. For example, battery life may not be an issue if you place the monitor on a shelf, desk, or table next to a power socket. However, if you want to be able to use the device on the go, battery life should be a major concern. 


Many monitors on the market use rechargeable batteries that provide around eight hours of battery life. While there are some exceptions with significantly more battery life, eight hours is the standard battery life on these devices.


Eight hours is enough to get through the work or school day, but it doesn’t allow much flexibility. On top of this, you will need to remember to charge the device every night, or it will be unusable in the morning. Adding another device which needs to be charged daily can be frustrating, and if you want to avoid this inconvenience, you might want to look for a device with better battery life.


Some devices will allow to power the device on and off to conserve battery life, but this can sometimes be an issue as most carbon dioxide monitors need to be powered on for a few minutes before they begin providing accurate readings. This means taking a quick reading on the bus or in a cafe without a few minutes of preparation is hard.


Ultimately, how you intend to use the device will dictate whether good battery life is needed or even whether a battery is required at all. Since battery life plays such a key role in how you can use your device, it should always be a priority you consider when purchasing a CO2 monitor.     



One of the biggest differentiators between carbon dioxide monitors are the connectivity options. You'll find some devices equipped with WiFi and Bluetooth, whereas others aim to provide an untethered user experience and do everything on the monitor.


The vast majority of carbon dioxide monitors with connectivity will have this in the form of a Bluetooth or WiFi connection to your phone. While some will have online dashboards and computer access, these tend to be less consumer-focused.


Connectivity means you don't need to physically see the device to monitor the CO2 concentration. Instead, you can use the accompanying app or the supported smart home integration (if applicable). While this is a nice feature to have, the most useful feature of connected devices is the ability to view historical data.


With connected monitors, data will be sent to the accompanying app or website, which can be analysed later. This allows you to identify trends in CO2 levels easily - do concentrations increase during the night? Does leaving doors open help to lower CO2 levels?


While these trends can be identified on a non-connected monitor, it is more difficult as you will need to be keeping an eye on the device to see how concentrations are being impacted.


On the other hand, many users will appreciate the simplicity of non-connected monitors. I, for one, hate having to download an extra app for every device I have, and non-connected devices are a great way to cut down on your digital mess while still getting a useful carbon dioxide monitor.

NDIR Sensor


When we talk about carbon dioxide monitors, we are generally referencing the monitor as a whole. However, the core of the monitor, and by far the most important part, is the carbon dioxide sensor housed within it.


There are a few different carbon dioxide sensors on the market, but the only sensor you need to know about is NDIR (non-dispersive infrared). These are the only sensors you should consider within consumer-level carbon dioxide monitors as they are both the most accurate and retain accuracy the best.


It’s not always apparent whether a carbon dioxide monitor uses an NDIR sensor, but most monitors that feature them will make it evident because this is a crucial selling point. You're looking at the right monitor if you see terminology like ‘NDIR sensor’ or ‘Dual-beam NDIR sensor’ or something along these lines.


NDIR sensors aren’t cheap, and you’re unlikely to find these sensors on any device under $50. There are a few options around this price point, but you still need to be careful until you reach about $100, as many carbon dioxide monitors use inaccurate sensors in this price range.


NDIR sensors can drift and gradually lose accuracy, so you will see some devices advertising dual-beam NDIR sensors. These dual beam sensors are designed to account for sensor drift and stay more accurate over the long term. However, there is research to show this may not be the case.


At the end of the day, the most important factor to look for when selecting a carbon dioxide monitor is whether or not it features an NDIR sensor - whether dual beam or single beam, you likely won’t notice a big difference.

Calibration options


Since NDIR sensors drift over time, you need to be mindful when it comes to calibrating the device. Carbon dioxide monitors have two ways they can recalibrated - manually and automatically. However, it’s important to note that not all carbon dioxide monitors will allow for both recalibration methods.


Autocalibration will allow the monitor to set a new baseline carbon dioxide concentration every set period - sometimes, it may be daily and sometimes weekly. Over this time, the monitor will find the lowest recorded concentration and set that as the baseline (usually 400 ppm). 


This is handy if the device is taken outside occasionally or sits in a room that isn’t always inhabited. Unfortunately, it can cause issues if the device isn’t regularly taken outside or used in an ambient environment, as the concentration may never drop to 400 ppm, meaning the device will take a higher reading as the baseline leading to inaccurate readings over time.


If your monitor isn’t in an environment that regularly sees a low carbon dioxide concentration, take it outside every few days so it can auto-calibrate itself with a new baseline. Alternatively, if you have a device that allows for manual calibration, you’ll want to start a new calibration cycle and leave the device outside while the process completes.


While there is no guideline for how often a carbon dioxide monitor should be manually calibrated, it’s a process you’ll likely want to carry out every month or sooner. Leaving a monitor uncalibrated for over a month will likely begin to skew readings.


If your monitor seems to provide inaccurate readings (you’ll get a sense of concentrations after having a monitor for a few weeks), this is a good sign that it’s time to recalibrate. Often if a monitor reading seems too good to be true (or vice-versa), it probably is.

Screen Size & Type


When selecting a carbon dioxide monitor, another important factor to consider is the screen type and visibility. Many monitors rely on E-ink screens, but these screens become unreadable in the dark. However, at night, some monitors include LED indicator lights that can be used to view the CO2 concentration quickly.


The benefit to E-ink screens is that they have high contrast and are always visible, provided there is enough light. This makes monitors with E-ink screens fantastic for use in offices or classrooms, and the screen will be easily and quickly viewable by anyone nearby. E-ink is also great for conserving battery life, and most monitors with long battery lives will use these screens.


Some CO2 monitors use more traditional screens, such as LCDs. While these are great to use inside, they can often be challenging to use outdoors as the screens don’t have enough contrast to be easily readable in bright environments. 


If you plan to use your monitor purely as a connected device, the screen may be irrelevant to you. At the end of the day, it’s most important to consider your requirements and in which environment you plan to use your device. All have their benefits and disadvantages!

Other sensors


Although the primary purpose of a carbon dioxide monitor is to monitor the carbon dioxide concentration, nearly all monitors also feature other sensors. For example, carbon dioxide monitors will often have a temperature and relative humidity sensor alongside the CO2 sensor. This is because, on many chips, these sensors are all integrated together.


To get a complete insight into indoor air quality, some monitors feature particulate matter (PM1, PM2.5 and PM10) and tVOC sensors alongside the selection mentioned above. In addition, you can even find carbon monoxide and nitrogen dioxide sensors on some monitors!


Whether or not these sensors are essential or desirable is up to you. A carbon dioxide monitor is the way to go for monitoring ventilation and checking transmission risk on the go, as larger devices with more sensors tend to have very poor battery life (or none at all).


However, if you’re looking for a static monitor to use in your home, you may want to consider a device with more sensors and, therefore, better coverage of all the pollutants that could impact your day-to-day life.

Conclusion - Choosing the Right Carbon Dioxide Monitor

Carbon dioxide monitors are very useful devices that can significantly impact the way you live. Since discovering them, I’ve changed many habits to accommodate better ventilation and indoor air quality. Perhaps more usefully, they take much of the guesswork out of knowing when to mask.


While most of the attention is currently on CO2 monitors due to their usefulness as risk-assessment tools, their double-purpose as productivity and health-improving tools should not be overlooked. If you want to control your indoor air quality, a carbon dioxide monitor is a tool well worth having!

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