Clearing the Air on Low Temperature Operation of Dehumidifiers

There seems to be a lot of confusion on the need for dehumidification when temperatures are low and the relative humidity is high. The real number we need to be concerned about is dew point, which is often overlooked and is confusing.  Dew point is the most accurate measurement of moisture in the air; it is the combination of temp and RH.  A low or dry dew point is anything below a 50-degree dew point.  This can fool a lot of people into thinking their dehumidifier should be running at temperatures of 40, 50 or even 60 degrees.

As temps get colder outside the conditions become dryer.  Air shrinks when it cools down, meaning that its’ ability to hold water decreases as well; this will drive your relative humidity up making you think that it’s moist in your home.  Warm air expands allowing for more water to be held; this will drive your relative humidity down.  When the temperature changes a single degree, your relative humidity (RH) will change an average of 2% – increase if the air is colder and decrease if the air is warmer.

Here are some more numbers for you – the following conditions all have a 45-degree dew point and are considered to be very dry conditions:

  • 95 degrees & 18%RH = 45 degree dew point
  • 80 degrees & 29%RH = 45 degree dew point
  • 70 degrees & 41%RH = 45 degree dew point
  • 65 degrees & 48%RH = 45 degree dew point
  • 60 degrees & 57%RH = 45 degree dew point (This is where there is confusion – no need to worry, the conditions are already dry enough!)
  • 55 degrees & 68%RH = 45 degree dew point
  • 50 degrees & 82%RH = 45 degree dew point
  • 45 degrees & 100%RH = 45 degree dew point

This chart tells you that dehumidification in not even needed when it’s raining out at 45 degrees and 100% RH – this air could easily dry your home.

These numbers are important when it comes to purchasing a dehumidifier based on strictly on low temperature operation – you most likely do not need dehumidification when it is below 60 degrees.  Santa Fe offers a full line of dehumidifiers that operate from 49 degrees min – 95 degrees max.

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