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%.

Current Models

Discontinued 50 Pint (70 pint 2012 DOE) Dehumidifiers

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
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

Discontinued 35 Pint (50 pint 2012 DOE) Dehumidifiers

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

Discontinued 22 Pint (30 pint 2012 DOE) Dehumidifiers

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)


  1. INGE BLEVENS says

    I got a Keystone. The Hygrometer is off by 20%. It reads 35 when it is 55% and I cannot get it to lower the humidity beyond that, which really stinks since mold grows at 40% and up.

  2. Ricky says

    Hi, I have 2 large household de-humidifiers at £120 each with 5 litre water tanks and 2 cheap £5 Chinese digital humidifiers. The expensive ones have always been about 10 to 15% apart than the cheap ones. So when the cheap handheld ones say 55 the big ones will say 45. Taking the average of these readings means I’m fairly happy were keeping the humidity around 50.

    Now many months later, and in Summer the gap has widened considerably. The little ones say 60 the big ones say 35. When switched on there is no water being pulled out of the big ones so I’m thinking the little ones are at fault. Surely £120 vs £5 is no competition. It’s just that both sets of humidifiers back each others readings up.

    Am I right to believe the big ones at 35% and how can I calibrate them to all read the same?

    Thank you.

  3. Debbie says

    I am on my 2nd Hisense #1151938 we have had one in the past and it worked great then the fan broke so we went to Lowe’s and bought another one brought it home ran it for 3 days and it never registered humidity below 66 I said it to 70 and it never shuts off and if it does shut off it only shuts off for a couple minutes and restarts I bought a hygrometer which is registering 46% humidity in the same room where the dehumidifier is and the dehumidifier is measuring 68% humidity we’re ready to take this one back to Lowe’s too very frustrating

  4. Peter says

    Question – I have a RPD-702WP Whynter 70 Pint Dehumidifier I just got. The temperature and relative humidity sensors seem way off to me. The dehumidifier unit is reading temperature of 56F and RH of 60-65%. When the unit turns on RH drops pretty quick(like 5% in 5 or so minutes) and strangely I see the temperature climb fast in those 5 minutes, by the time the unit turns off, temperature reading is at 62F, RH is at 55%.

    Then the cycle begins again in the next 15 minutes(give or take 10 minutes). temperature reading on the unit in that about 15 minutes goes back down to 56-57F, RH goes back up to 60-65% and unit turns back on.

    The unit has done these cycles all day long and I worry that isn’t right… At this rate the unit is turning its self on and off 72 times in a 24 hour period.

    Note: I have two different AcuRite – Thermometer & Hygrometer Gauge which I left next to the dehumidifier unit all day. Both gauges showed temperature range of 61-63F and RH 49-52% for the whole day. So they both barely moved while this dehumidifier went all over the place in a 20 minute span. Any advise on the matter? Also I have the dehumidifier in open space as I know that can cause issues.

    • Admin says

      The dehumidifier may be defective but you won’t know for sure until you use it in an enclosed space. We recommend moving it to an enclosed space (a room with a closed door will do just fine) and seeing if it exhibits the same behavior. If it does, we recommend calling the manufacturer for further troubleshooting.

      • Javier Hoyos says

        Hello: I just bought a toshiba 70 pints. and it does the same thing: I set it to 45… the humidistat goes up to 49 and then the unit will turn on. then in about 3 minutes maybe 4 the reading goes to 44 and at that point the compressor will shut off. and the fan will continue for another 3 minutes before the fan shots off. by that time, the humidistat is reading 46 or 47. it will remain off for about 3 or 4 minutes and then the humidistat goes to 49 and back again to the same … this is the second unit. it does the same…. also on the instructions say to run the unit in continuos operation for 24 hours.. I did and by hour 21 the back of the unit started to ice up… not frost, but ice… I turn the continuos operation to manual… my basement is air conditioned 72 and heated… why a unit will ice up at 72 degree? call toshiba and they gave me the usual run around… thinking about returning this unit back to home depot…. what you guys think? a unit that turns on an off every 10 minutes is not so good on my electric bill…… and by the way I have a hygrometer and reads 44 % and it does not goes up and down…like on the unit……. please advise me……. thanks…..

        • Duncan says

          IMO, your problem is a design flaw in many units. Manufacturers place the sensor INSIDE the unit. Unit runs, pulls in ‘dry’ air, unit shuts off. As the unit is full of condensate just created, humidity inside the unit is very high, within a minute, unit thinks it needs to turn on again (rinse and repeat). I moved the sensor external to the unit, problem solved. Instead of two minutes on, two off. It now runs for say five on, ten off. I think it is an industry dirty secret. No wonder some complain of units only lasting a year or two.

  5. 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%.

  6. 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

Have a question or comment? Let us know below.

Your email address will not be published.