Air-quality numbers are objective. Air-quality experience is not. Two rooms with identical PM2.5 readings can feel very different if their temperature, humidity, dew point, VOC content, and air velocity diverge. Comfort comes from the combination, which is why this article looks at the readings together rather than one at a time.
The single strongest factor is the combination of temperature and humidity, captured by dew point (see dew point) and apparent temperature (see apparent temperature). At 22 °C and 30% RH a room feels crisp; at 22 °C and 75% RH the same room feels muggy. Terrestream shows humidity alongside temperature, so the two rooms read differently even when the temperature is identical. Fanger's PMV model is the canonical reference for thermal-comfort integration.
Temperature and humidity are not the whole story. The ASHRAE 55 comfort standard also counts radiant heat, such as the warmth of a sunny window or the chill of a cold wall, along with air movement, clothing, and activity, and notes that comfort varies from one person to another; the Terrestream sensor measures air temperature and humidity, not radiant heat or air movement. VOCs can matter too: EPA lists eye, nose, and throat irritation and headaches among the possible effects of VOC exposure, and notes that many VOCs are consistently more concentrated indoors than outdoors. The VOC index on Terrestream is relative, with 100 meaning "the same as recently," so a rise tells you something new is emitting, not how the room will feel.
Terrestream does not report that "the air feels off," and it has no model that folds all of these inputs into one comfort score. It shows the readings side by side, with temperature next to humidity, and it flags specific conditions the data support, such as a room that stays damp or CO2 that keeps building. When a room feels wrong and no single number stands out, look at the combination, starting with temperature and humidity together: readings that are each within range can still add up to discomfort, which is why comfort standards such as ASHRAE 55 treat thermal comfort as a combination of factors rather than a single threshold.
References
- ASHRAE Standard 55 - Thermal Environmental Conditions www.ashrae.org
- NOAA NWS - Dew point vs relative humidity www.weather.gov
- Fanger - Assessment of thermal comfort in practice (PMV) doi.org
- EPA - Volatile organic compounds and indoor air www.epa.gov
