When you think about the components of indoor air quality (IAQ), you probably think about factors like CO2, particulate matter, temperature, etc. However, one parameter that many people overlook when it comes to air quality is humidity.
We typically hear about humidity in the context of weather forecasts and outdoor air, but its impact on indoor air is just as substantial. It not only affects occupant comfort and experience but also plays a huge role in determining the overall health and longevity of your building or space.
In this article, we’ll be diving into everything you need to know about humidity — what it is, how it affects air quality, what levels you should maintain, and how to use humidity monitoring data to optimize your indoor environment.
Humidity is the measurement of how much water vapor is present in the air. There are several ways to measure it, but the most common metric is relative humidity (RH), a percentage that compares the amount of water vapor in the air to the maximum amount that the air can hold at a given temperature. Warm air can hold more moisture than cold air, which means that the same amount of moisture can feel very different depending on the temperature.
For example, air at 30ºC (86ºF) can hold nearly 28 grams of water per cubic meter. But at 8ºC (46ºF), the same cubic meter of air can only hold about 8 grams of water vapor. That’s why the air on a hot summer day feels “heavier” than the air on a cold winter day.
The other metric that you might see is absolute humidity, which describes the actual mass of water vapor present in a unit volume of air (e.g., grams per cubic meter). However, because the impact of humidity is largely tied to the current temperature, the metric you should pay attention to for IAQ monitoring purposes is RH.
Humidity is a natural part of the Earth’s atmosphere. It always exists outside, meaning it directly impacts the air inside, in addition to a number of indoor sources. Understanding these sources is key to identifying ways to either increase or decrease humidity to optimize your workplace environment.
The primary driver of atmospheric humidity is the Earth’s water cycle. Water is constantly evaporating from bodies of water and turning into water vapor that mixes in with the air, and it leaves the air via condensation, turning into either rain or dew.
When outdoor air enters a building — whether through HVAC systems, natural ventilation, or through gaps in doors or windows — it brings moisture in with it. This can increase indoor humidity in warmer months or drastically reduce it in the winter when the air is cold and dry.
Indoor humidity comes from a variety of everyday activities, whether you’re at home or at work. At home, common sources include cooking, showering, and drying clothes inside. In the workplace, moisture can accumulate in kitchens, break rooms, restrooms, shower facilities, and even from cleaning operations.
However, one of the largest sources of humidity in the built environment is the occupants themselves. People are constantly releasing moisture into the air via respiration and perspiration, and, if you’re in a crowded or poorly ventilated space, this moisture can build up rapidly and raise indoor humidity to an uncomfortable level.
HVAC systems also play a major role in determining indoor humidity levels. Well-designed systems can effectively regulate moisture levels by dehumidifying the air during cooling periods and increasing humidity when the air is cold and dry.
However, an HVAC system that is poorly designed or isn’t properly maintained will struggle to control moisture levels. This is often due to a lack of proper conditioning, when the system fails to remove moisture from the outdoor air supply and, as a result, introduces excess humidity into the indoor environment.
There are slight variations in how different regulatory bodies and standards define the ideal humidity range:
For the purposes of this article, we’ll pull from each of these standards and say that the optimal indoor humidity level is 30% to 60% — a range that is widely accepted across the industry. This range strikes a balance between enhancing comfort and health while also preventing moisture-related issues. Having too much or too little moisture in the air can cause potentially serious problems for your building and your occupants.
The Role of Humidity in WELL Certification
Humidity is a core part of WELL’s Thermal Comfort concept. Measuring and maintaining proper humidity levels can help you achieve one precondition and two optimization points across three features:
T06 (Thermal Comfort Monitoring): You can earn the optimization point for this feature by installing continuous monitors for relative humidity and dry bulb temperature and sharing the data with occupants. This must be verified by a letter of assurance from an engineer. (Note: By meeting the requirements of T06, you can also satisfy precondition T01 with no extra work!)
T07 (Humidity Control): To earn the optimization point for this feature, you have to prove that your indoor humidity level stays between 30% and 60%. You can verify this with sensor data, a letter of assurance, or a technical document.
Because of the variety of both indoor and outdoor sources, humidity levels almost never stay the same. That means that your humidity management tactics will likely change on a regular basis. Here’s a quick guide to help you interpret your humidity levels and understand what actions you should take based on your RH readings.
|
Relative Humidity (RH) |
Status |
Recommendations |
≥ 70% |
Very High |
Use a dehumidifier to remove excess moisture. Increase ventilation and open windows/doors if outdoor levels are low. |
60% – 69% |
High |
Monitor levels closely, especially during humid weather. Use ventilation and consider running a dehumidifier during peak humidity times. |
30% – 59% |
Optimal |
This is the ideal range for comfort and health. Continue your current ventilation and humidity control practices. |
25% – 29% |
Low |
Monitor levels closely, especially during cold, dry weather. Consider using a humidifier if occupants report discomfort. |
≤ 24% |
Very Low |
Use a humidifier to add moisture to the air (read more about how humidifiers affect IAQ and learn safe tips for use). Reduce ventilation if possible, especially during very cold, dry weather. |
Monitoring humidity isn’t just about making sure you maintain a comfortable environment — it’s crucial for safeguarding occupant health, protecting building materials, and optimizing your overall IAQ. With continuous, real-time data, you can track humidity patterns, uncover issues, determine the causes, and make more informed decisions for ventilation, humidification, and dehumidification.
If you’re ready to start measuring humidity, the first step is choosing a monitor that fits the needs of your space. The requirements and considerations change in different settings, whether you want to monitor humidity in your home or at your workplace.
At home, the best option is to buy a smart humidity sensor, or hygrometer. Smart sensors are key because they not only collect real-time data but also offer app connectivity so you can easily track your levels from any device, anywhere.
In the workplace, you have a couple of options, depending on your goals and how you want to use your data. The first option is to install basic temperature and humidity sensors throughout your building or space and, if you use a building management system (BMS), make sure to find a sensor that integrates with your BMS so your building can automate humidity and temperature control.
The second option is a multi-parameter indoor environmental quality (IEQ) monitor, which measures both IAQ and IEQ parameters at the same time, giving you much deeper insights into your indoor environment.
This has always been a recommended approach and preferred approach by workplace leaders and building operation teams, as you can “kill two birds with one stone” and gain a complete picture of your indoor environment. The comprehensive data from these multi-parameter monitors makes it much easier to troubleshoot poor air quality and optimize your workplace for health and well-being.
Interested in learning more about humidity monitoring? Reach out to a member of our team today!