Lesson 3 – Humidity: Overrated for Comfort, Critical for Health
Lesson Objective
Understand why humidity is often blamed for comfort problems even when it is not the real cause, and when humidity control actually becomes critical for health and building performance.
The Common Humidity Misconception
Humidity is one of the most misunderstood HVAC variables. Many comfort complaints are quickly attributed to “low humidity” or “high humidity,” even when relative humidity is within acceptable limits. In most offices, humidity has a smaller impact on thermal comfort than people expect.
Comfort vs Health
Within normal ranges, humidity does not strongly affect thermal comfort as long as temperature and air movement are reasonable. However, humidity plays a major role in respiratory health, odor perception, and the growth of mold and bacteria. This is where humidity control truly matters.
Example 1 – Dry Air Complaints in Summer
Occupants complain of dry eyes and throat irritation during summer operation. Temperature is stable and within range. Relative humidity is around 40–45%, which is acceptable. The real cause is high air velocity and long exposure to moving air, not “dry air” itself.
Over-Dehumidification
Many HVAC systems remove more moisture than necessary. Low supply air temperatures combined with high airflow rates often result in excessive dehumidification. This creates discomfort, increases energy use, and may lead to unnecessary humidification attempts later.
Example 2 – Fighting the System
An office building operates with very low supply air temperatures to control sensible load. Relative humidity drops significantly. The operations team considers adding humidifiers, while the real solution should be higher supply temperatures or better air distribution.
High Humidity and Real Risk
High humidity becomes a serious issue when it exceeds acceptable limits for extended periods. It increases the risk of mold growth, material degradation, and indoor air quality problems. In such cases, humidity control is no longer a comfort preference—it is a health requirement.
Example 3 – Mold Complaints
A space feels “okay” temperature-wise, but occupants notice musty odors and health complaints increase. Relative humidity regularly exceeds 60%. The problem is not comfort—it is biological growth caused by poor moisture control and insufficient dehumidification.
Winter Humidity Expectations
In cold climates, maintaining high indoor humidity during winter can cause condensation on windows and within the building envelope. Lower humidity levels may be necessary to protect the building, even if occupants perceive the air as dry.
Key Insight
Humidity is rarely the primary cause of comfort complaints, but it is a major factor in health, air quality, and building durability.
Key Takeaway
Do not chase comfort complaints by adjusting humidity blindly.
First, identify whether the issue is comfort perception, air movement, or a real moisture-related health risk.
Reflection
In your projects, how often is humidity blamed—
and how often is it truly the root cause?