Relative Humidity (RH) and Actual Humidity (AH) Explained

  • Absolute humidity is the measure of water vapor (moisture) in the air, regardless of temperature. It can be expressed several ways: grams of moisture per cubic meter of air (g/m3), grains of moisture per pound of air (gpp), or dew point (°F or °C). It is recommended to maintain a continuous absolute humidity level where the dew point is 55°F or less.
  • Relative humidity also measures water vapor but RELATIVE to the temperature of the air. It is expressed as the amount of water vapor in the air as a percentage of the total amount that could be held at its current temperature. Relative humidity has frequently been used to describe indoor air quality, with a target of 40-60% humidity as the window to minimize growth of microbes, spores, and mold.
  • Warm air can hold far more moisture than cold air meaning that the relative humidity of cold air would be far higher than warm air if their absolute humidity levels were equal.
  • Humidity levels impact both comfort and health of building occupants.
  • Dehumidifiers are the most common mechanical way to manage humidity. They help reduce indoor moisture, especially in regions with high outdoor humidity levels. Northern regions tend to suffer from very low humidity levels during the winter season, which can be uncomfortable for building occupants.
poor indoor air quality can trigger asthma

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