How do I calculate the possible error at a certain RH? Does this mean that it has a lower error at 40% than at 90% ?


In theory, "+/- 5% in range of 30%-90%" means that...

  • if you set the humidistat dial to 30%, it might actually be set to anywhere from 25% to 35%
  • if you set the humidistat dial to 90%, it might actually be set to anywhere from 85% to 95%

In reality, consumer humidistats generally aren't very precise (e.g. relatively less precise than most thermostats). Unless you have an absolute need for a precise humidity level, I'd just set it to what feels good and not worry too much about the absolute humidity level.

  • All I want is to make sure I can compare the humidity in different rooms of my basement and that I am safely under the mold formation level – MiniMe May 28 '16 at 19:33
  • Measuring the humidity where the mold might form would probably be more accurate than trusting the humidistat. – Daniel Griscom May 28 '16 at 20:13
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    I have hygrometers in each of the rooms that I am monitoring but they don't seem really in line with each other. I had them in the same room with the DH and all 4 of them (the DH and the three hygrometers) indicated different things for the same test spot I guess the salt method to find the error margin for each of them is required – MiniMe May 28 '16 at 20:19
  • Yes @user2059078, calibrate your hygrometers with the salt method (the $10 digital ones I got at Amazon were spot on.) You could then calibrate your dehumidifier's humidistat by putting a hygrometer in the same room and adjust until it is stabilizing at the humidity level you'd like. By the way, I just read a study on the effectiveness of keeping down humidity for controlling dust mites. Keeping it consistently <51% eliminates almost all mites. – glenviewjeff Jun 1 '16 at 1:24

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