Measurements · Meteorology
Dew Point
Also known as dewpoint temperature, sample dewpoint
Dew-point temperature; the temperature at which air becomes saturated.
What it is
What is dew point?
Dew point is the temperature to which air must be cooled, at constant pressure, for the water vapor in it to begin condensing into liquid; in other words, the temperature at which the air becomes saturated. Unlike relative humidity, which changes with temperature, dew point is an absolute measure of how much moisture the air actually contains: a dew point of 15 °C means the same water-vapor content whether the surrounding air is warm or cool. It is derived from temperature and relative humidity, or measured directly with a chilled-mirror hygrometer. Dew point, temperature, and RH are three views of the same moisture state.
Health and operational effects
Dew point is the most reliable single guide to muggy discomfort. Because it is independent of temperature, a high dew point (roughly above 16–18 °C) feels oppressive whatever the thermometer says, since the humid air limits sweat evaporation. That makes it a better outdoor comfort indicator than relative humidity alone, and it is an input to the heat index.
Operationally, dew point is the parameter that governs condensation. Whenever a surface (a window, a wall, a chilled pipe, a freshly machined part) falls to or below the air's dew point, moisture condenses on it, bringing mold, corrosion, electrical faults, and product spoilage. Compressed-air systems, refrigeration, drying processes, and building envelopes are all managed against dew point.
How it is measured
How Dew Point Is Measured
In most monitors dew point is calculated from a co-located temperature and relative-humidity measurement using a standard psychrometric relationship, so its accuracy inherits that of the capacitive RH sensor and the temperature element feeding it. For demanding applications the reference method is the chilled-mirror hygrometer, which actively cools a small mirror until condensation forms and optically detects the onset, reading dew point directly and very accurately. Chilled-mirror instruments are used in laboratories and industrial process control; calculated dew point is standard in building, meteorological, and indoor-air-quality monitoring.
Built into Aethair PRO and Aethair IAQ2
Measured by the monitor's own sensors, calibrated before it ships: nothing to add.
An instrument on Thiamis5
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing dew point monitoring
Because dew point is derived from temperature and humidity, the sensor is sited by the same rules: in the occupied or monitored zone, away from direct moisture sources, supply air, and heat sources that would bias the underlying readings. For condensation-risk assessment the informative comparison is between the air's dew point and the temperature of the coldest nearby surface, so pairing an air dew-point reading with surface-temperature information around cold spots, glazing, and thermal bridges is far more useful than a single room value.
Every device and option that measures Dew Point 7
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
Aethair PRO built-in sensors | Built-in sensors | Aethair PRO | |
 Aethair IAQ built-in sensors | Built-in sensors | Aethair IAQ | |
 Airmar · 110WX, 110WXS, 120WX… | Weather Stations | Thiamis | |
 Davis · Davis Wizard III, Davis Wizard II, Davis Monitor… | Weather Stations | Thiamis | |
 Lufft · WS100, WS200, WS300… | Weather Stations | Thiamis | |
 Gill Instruments · MaxiMet-GMX100, MaxiMet-GMX200, MaxiMet-GMX240… | Weather Stations | Thiamis | |
 AethLabs · MA200, MA300, MA350… | Specialty Air Analyzers | Thiamis |
Where it is monitored
Solutions That Monitor Dew Point
Each one links to the solution page showing what that industry measures it for.
HVAC & Building Management
Often addedMonitor ventilation and filtration, with data for your BMS
Weather Stations & Meteorology
Often addedProfessional multi-parameter weather monitoring
Article Library
Reading on Dew Point
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Questions
Dew Point FAQ
What is the difference between dew point and relative humidity?
Relative humidity is a percentage of the air's current capacity and therefore changes as the air warms or cools, while dew point is an absolute temperature that reflects the actual water-vapor content. Two rooms can share the same RH but very different dew points, which is why dew point is preferred when comparing moisture across different temperatures.
What dew point feels humid?
As a rough guide, dew points below the low teens feel comfortable, the high teens feel noticeably muggy, and values above about 20 °C feel oppressive, regardless of the air temperature. Because it is temperature-independent, dew point is a more consistent comfort cue outdoors than relative humidity.
Why does dew point predict condensation?
Condensation forms wherever a surface is at or below the dew point of the air touching it. So the dew point tells you the temperature at which windows, pipes, and walls will start to get wet. Keep every surface above it and no condensation occurs; that is the basis of managing mold and corrosion.
How do I monitor dew point?
The Aethair family (Aethair PRO and Aethair IAQ) derives dew point continuously from its built-in temperature and humidity sensors, so no separate instrument is needed for indoor condensation and comfort monitoring. Use the configurator to combine dew point with temperature, humidity, and, for surface-condensation studies, additional sensors connected through Thiamis.
Monitor Dew Point on the Record
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A 30-minute call: you tell us about your application, then we demo the solution for it.