Hygrometer Accuracy

Almost all dehumidifiers are equipped with a built-in hygrometer that measures the ambient air’s relative humidity. This measured value is what is normally displayed on the dehumidifier’s control panel. The dehumidifier’s job is to attempt to achieve a room humidity level that matches your set desired humidity level. It can only do so if it can measure the room humidity level itself and it does so using its built-in hygrometer.

Most of the units we tested were equipped with a hygrometer that would read and display relative humidity in 1% increments. Some units only displayed the ambient air’s humidity level in 5% increments. Not surprisingly, those units equipped with hygrometers that read humidity levels in 1% increments were generally more accurate and precise than those units that could only display readings in 5% increments.

Why should you care about hygrometer accuracy? Let’s take a look at an example of why it’s important. Let’s say you set your dehumidifier to a desired humidity level of 50% RH (relative humidity). Your dehumidifier’s hygrometer isn’t very accurate reading humidity levels 5% below the actual room humidity. Thus it reads 50% RH when the actual room humidity is 55% RH. This means that if you set your dehumidifier to 50% RH it will never actually achieve 50% RH. Instead, it will automatically shut off when it reads 50% RH (the level at which you set the desired humidity level) but this reading is inaccurate. It may be reading 50% RH but the actual room humidity is 55% RH.

Test Results

The chart below shows the hygrometer accuracy of each of the dehumidifiers we tested. In this chart, the lower the number, the better. The chart shows how close the particular unit’s built-in hygrometer reading was to the actual room humidity. Thus, a result of “2%” indicates that the dehumidifier’s reading was within 2% of the actual room humidity. For example, at an actual room humidity level of 50% the dehumidifier would read either 52% or 48%.

70 Pint Dehumidifier Hygrometer Accuracy

Manufacturer and Model
Accurate To Within This %
Frigidaire FFAD7033R13 to 4
Keystone KSTAD70B2 to 3
Danby DDR70A2GP1, mostly on the dot
Honeywell DH70W1, mostly on the dot
RCA RDH7051 to 2
GE ADEL70LR5
Haier DE65EM5 to 6
Kenmore KM70NA
Whirlpool AD70GUSB4 to 6
Hisense DH-70KP1SLE1, mostly on the dot
Friedrich D70BP1, mostly on the dot
SPT SD-72PE1, sometimes on the dot
Haier HM70EP4 to 6
Delonghi DD70PE3 to 4

50 Pint Dehumidifier Hygrometer Accuracy

Manufacturer and Model
Accurate To Within This %
Frigidaire FFAD5033R13 to 5
Keystone KSTAD50B1, mostly on the dot
Friedrich D50BP5 to 6
Delonghi DD50PE1 to 3
SPT SD-52PE 1, sometimes on the dot

30 Pint Dehumidifier Hygrometer Accuracy

Manufacturer and Model
Accurate To Within This %
Frigidaire FFAD3033R13 to 4
Hisense DH-35K1SJE52 to 3
GE ADEL30LR2 to 7
Haier DM32M-LNA (manual hygrometer)

Important Note

All the dehumidifiers we tested except for the GE 70 and 30 pint units read the ambient room humidity in 1% increments. GE units only read humidity levels in 5% increments. Due to this limitation the GE units were not able to be as precise in their readings from the get-go. Keep this in mind as you evaluate the data above.

Comments

  1. Olivia Verde says

    Got the the FFAD30333R1 2 weeks ago. In your chart it reads 3-4% variability in the hygrometer. Let’s say set for 40, and the read-out reads 40, does that mean the actual could be anywhere from 36 to 44? that seems to be a pretty broad range. And is it more likely to be higher of or lower? or can go either way? When I have it set for 40, it seems to rarely go up or down from that. It reads 40 almost all the time if I have it set to 40, which I guess at least it shows it’s within the range in your chart. 15′ away from the unit, my humidistat reads 45. No big deal. It rarely goes off in here (1 bedroom apt, 650 SF). I admit I have been opening front door a few inches off and on, because it’s been 88-89 in here. We’re been in a mild heat wave here in L.A. (I didn’t get the 50 because I didn’t want the water bucket to be any heavier than 1.7 gallons (though it never seems that much when I pour it out. Perhaps the full 1.7 is to the very top of the bucket, which of course, it is set to not fill up to the top! :) Thank you. I am trying to get rid of mites, and it has indeed almost stopped them entirely from biting me. Yea! Thank you! (I actually like humidity, but so do the mites! :)

    • Admin says

      For all of the dehumidifiers we tested, if their humidity reading was off, it was always below the actual humidity in the room. This means that in your situation the dehumidifier’s read-out of 40% RH could be describing an actual range of 40 to 44% RH, not 36 to 44%.

  2. Robert carbone says

    I have the Freidrich D70BPA. I returned one for the same issue and this one is going back as well. I set it at 50. It removes moisture great and goes down to 45 and then shuts off. Great! BUT within 5 minutes the humidistat will shoot up to 55 and the unit will come back on. I have 2 individual humidistats in the room and both will still be reading 45 or maybe 46. Freidrich Sensor placed too close to the coils? This happened on two units. Think the best dehumidifiers are the ones that the fan stays on after the compresser kicks off.
    Opinions? Thanks

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