Temperature And Humidity

Being aware of the ambient air temperature of the room you’re trying to dehumidify is another tool in your toolbox of combating any humidity problem. The relationship between temperature and humidity is more complicated than you might expect. Instead of showing you charts and graphs and having an extensive discussion explaining this relationship we’ll simply highlight its end result – the lower the air temperature, the less amount of moisture needs to be in the air for the same humidity reading. You might have heard before that “the lower the temperature, the less moisture the air can hold”. While this isn’t technically true (air can’t actually “hold” moisture) what it implies is correct. You see this phenomenon in action every day when you take a shower. You’ve probably noticed that the warm moist air created by your shower condenses onto cold surfaces in your bathroom such as your bathroom mirror. The cold air surrounding the cold surface can’t “hold” nearly as much moisture as the warm moist air surrounding it. What it cannot “hold” condenses as liquid water on the mirror.

Relative to the current discussion, the important point here is that a block of air at 50% relative humidity and 50° F “holds” much less moisture than that same size block of air at 50% relative humidity and 90° F. To further explain this phenomenon let’s imagine two different scenarios. In one scenario you have a moisture problem in which the ambient air is at 80% RH and the ambient air temperature is 90° F. You turn your dehumidifier on and set it to a desired humidity level of 40% RH which it reaches after a few hours of operation. In another scenario the initial ambient air temperature is 50° F. The starting RH is again 80% and again you set your dehumidifier to a desired humidity level of 40% RH. Again it achieves this desired humidity level in a few hours. Which scenario results in more moisture removal?

The answer here is that much more moisture is going to be removed in the first scenario because the warm air at 80% RH “holds” much more moisture (that can be removed) than the colder air at 80% RH. Thus, you can expect the dehumidifier’s condensate collection bucket to fill up with much more moisture in going from one extreme humidity level to another at higher temperatures than you can at lower temperatures.


  1. Tommy says

    Currently running my dehumidify in my uninsulated garage. It’s sealed up pretty well, but right now it is about 55F and the humidity is 47%. The dehumidifier is set to 60%, but it keeps rising above that and turning on. I can’t figure why it’s turning on so frequently with the outside being 47%. It did rain all day yesterday and a little today.

    • Admin says

      The unit’s humidistat may be poorly calibrated. Otherwise, the area immediately surrounding the dehumidifier may simply be at a higher humidity level.

    • Anonymous says

      Please check dehumidifier sensor , is that they are not open or got block by some object not able to get air from area

  2. M Thurston says

    I close my house in the winter and drain the pipes. I am not there between November and May, and in the winter months, the house temperature goes well below freezing. In the fall and spring, the humidity is high, however. Is there a dehumidifier I can leave running which will shut off at a set temperature (@ 40 degrees F) and then turn back on at that temperature? I don’t want it to get frost on the coils or to have any water or condensation freeze the unit in the winter. Thank you.

    • Admin says

      Most compressor based units have an auto-defrost feature that will shut off the unit automatically when frost builds up on its evaporator coils.

  3. Abullock says

    We have finished basement. If I am running dehumidifier should I shut off ac vents or keep them open. Without dehumidifier the RH ranges from 60-65% on dry outside days with room temp at about 68F. (AC vents open). Running dehumidifier raises room temp to about 70. Should I use both ac and dehum. At same time???

    • Admin says

      We would recommend first trying to adjust/troubleshoot your AC system to see if it can reduce humidity more. It should be able to get RH to comfortable levels running by itself. If that proves unsuccessful you can certainly run both the AC and dehumidifier at the same time. Yes, running the dehumidifier will increase temperatures slightly but the AC will cool things right back down again.

  4. John IL says

    Our home has a full basement but unfinished. Its cold in Winter average temp 59 degree’s but humidity is low. But in Spring and Summer humidity rises faster then temp so we have trouble addressing humidity with a standard de-humidifier. Were at end of May and temp down there is 62 degree’s and I know from experience de-humidifier coils will freeze up. I tried opening the two windows in wells of one wall to get air flow and even ran a fan. It helps but we have had a lot of rain and humidity and our floors have always shown marks where stuff sits. Cardboard always get’s damp and we know others have similar issues in neighborhood. Our sump pump runs every minute when it has rained. So we know sub floor water issue are a problem.

  5. ProDigit says

    I believe there is somewhat of a sweet spot in terms of temperature.
    When the air gets too hot, and the cold side heatsink can’t keep the water cool enough…

  6. Jason says

    We are looking for a unit that would bring a ~250 sq ft room that normally sits between 40-60% humidity down to 20% humidity. Have you come across anything that would accomplish this? Thanks!

  7. Theo says

    I am trying to compare to dehumidifiers that are said to extract both 20L/24h of moisture.

    However the first one, branded Singer, states 20L/24h capacity at 30 degrees Celcius at 80% RH, with max voltage consuption of 380W and the second one, branded Inventor, states 20L/24h capacity at 26,7 degrees Celcius at 60% RH, with voltage consumption 260W measured at this conditions (26,7 degrees Celcius at 60% RH).

    As I do not have the knowledge and the expertise could you please advise me which of the of two (Singer or Inventor) is more capable and more energy efficient?

    Thank you

  8. Hugh says

    I understand that colder air holds less moisture but how does that apply to mold formation? I regularly read that a relative humidity level of 50% or higher is conducive to mold formation but at what temperature. It seems to me that the actual amount of moisture in the air is the key to mold formation and therefore it is insufficient to say just 50% relative humidity will cause mold. If you know, at what room temperature is 50% conducive to mold? 60 degrees, 65, 70, 75, 80, or ? My dehumidifier recommends keeping the relative humidity at 50% but goes on to say “dehumidification is not usually needed during conditions of low room temperature” but doesn’t define “low room temperature”. My basement is at 65 degrees and 52% relative humidity. Should I be concerned about mold formation? I don’t want to run my dehumidifier if it isn’t really needed. Thanks for any help you are able to offer.

    • Anonymous says

      Mold generally does not grow in cold environments. Warm, humid conditions are ideal for mold growth. Most molds need temperature of 70 degrees Fahrenheit (20 degrees Celsius) or more to grow. Air conditioners to regulate the temperature of your house can help prevent mold growth. Thus, if its below 70 degrees, theres no need to worry about the humidity whether its 50% or 80%.

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