Energy Efficiency

How We Tested For Power Usage

To determine each dehumidifier’s energy efficiency we first made sure that the exact same conditions applied to each of our tests. First and foremost we made sure that the relative humidity of the ambient air remained consistent throughout all tests. We set the relative humidity to 50% because it was easy to do and allowed us to maintain a consistent humidity level throughout the test procedure. It would have been much harder for us to test at a greater humidity level because the dehumidifier would dehumidify so quickly that it wouldn’t keep the room at a consistent humidity level throughout the duration of the test.

A consistent humidity level was important for the following reason – how much power any particular dehumidifier draws directly correlates with the ambient air’s relative humidity. In the simplest terms, think of the dehumidifier’s internals “working harder” at higher humidity levels. Thus the dehumidifier draws more power at 90% RH (or any other relative humidity percentage greater than 50%) than it does at 50% RH. The Danby DDR70A2GP, for example, would draw 750 watts of power at 90% RH and only 590 watts of power at 50% RH. It was therefore of utmost importance that we maintained a steady and consistent room humidity level while testing each dehumidifier for power usage.

Other than keeping the environment consistent throughout each test we also set each unit to high fan speed and waited until the compressor would cycle on prior to measuring power usage. Thus, each unit’s power usage was measured at 50% RH, on high fan speed, and with the compressor cycled on. Initially, we also tested power usage on low fan speed but soon noticed that the difference between power draw on high and low fan speed was negligible (only a few watts). Thus, we didn’t feel like it was worth our time to test each individual unit for its power usage on the low fan speed setting.

Test Results

Below you’ll find the results of our testing. You can sort the tables below by clicking on the up/down arrows next to each column heading. Clicking on the down arrow will sort the dehumidifiers we tested from most energy efficient to least energy efficient. Clicking on the up arrow will reverse the list from least energy efficient (most energy usage) to most energy efficient (least energy usage). Note that we’ve also included the manufacturer’s specification for each model’s power usage (advertised wattage) in the tables below. All power usage numbers are in watts.

70 Pint Dehumidifier Power Usage

Manufacturer and Model
Real World Wattage
Advertised Wattage
Frigidaire FFAD7033R1632745
Keystone KSTAD70B590720
Danby DDR70A2GP590770
Honeywell DH70W642820
RCA RDH705571720
GE ADEL70LR632745
Haier DE65EM590690
Kenmore KM70590NA
Whirlpool AD70GUSB590746
Hisense DH-70KP1SLE610746
Friedrich D70BP620746
SPT SD-72PE600720
Haier HM70EP667750
Delonghi DD70PE655680

50 Pint Dehumidifier Power Usage

Manufacturer and Model
Real World Wattage
Advertised Wattage
Frigidaire FFAD5033R1493530
Keystone KSTAD50B439520
Friedrich D50BP462533
Delonghi DD50PE439NA
SPT SD-52PE 450520

30 Pint Dehumidifier Power Usage

Manufacturer and Model
Real World Wattage
Advertised Wattage
Frigidaire FFAD3033R1319320
Hisense DH-35K1SJE5352NA
GE ADEL30LR356405
Haier DM32M-L404465

It’s very important that you realize that even though smaller capacity units draw less power per unit time than large capacity units, they will be operating for a much longer time to remove the same amount of moisture.

Here’s what we mean. Let’s say you have a 1000 square foot space that you need to dehumidify. That space contains a set volume of air that is “holding” a set amount of moisture that needs to be removed from the air before the desired humidity level in the space is achieved. Let’s just pick an arbitrary number for the volume of moisture in the air – let’s say it’s 50 pints of moisture in the air. That 50 pints of moisture (that will eventually drip down into the dehumidifier’s condensate collection bucket) needs to be removed from the air by the dehumidifier. Let’s say, hypothetically, that it takes 24 hours for a 30 pint dehumidifier to remove this set amount of moisture from the air within this imaginary 1000 sq ft space.

Our moisture removal tests showed that 70 pint units take about 30% as long as 30 pint units to dehumidify a 50 sq ft space from 90% down to 40% relative humidity. 50 pint units take about 50% as long as 30 pint units to dehumidify the same space “holding” the same amount of moisture from 90% down to 40% relative humidity. The bottom line – 70 pint units take 30% as long as 30 pint units and 50 pint units take 50% as long as 30 pint units to dehumidify the same space at the same initial humidity level.

Now let’s go back to our imaginary scenario of a 1000 square foot space “holding” 50 pints of moisture which takes a 30 pint dehumidifier 24 hours to dehumidify. By extrapolating our moisture removal test results we can now estimate that a 70 pint unit will take 70% as long as a 50 pint unit and 50% as long as a 30 pint unit to dehumidify the space from high humidity down to an acceptable level of humidity. This means that in the current example after applying the ratios we obtained from our moisture removal tests, a 30 pint unit takes 24 hours, a 50 pint unit takes 12 hours, and a 70 pint unit takes 7.2 hours to dehumidify our imaginary 1000 sq ft space.

Now let’s apply what we’ve learned to the real world where you’re going to have to pay a certain amount of money for the energy your dehumidifier uses to do its job and dehumidify the space you need to dehumidify.

Real World Costs Of Dehumidifier Ownership

Your monthly power usage is billed by your utility company by the KWH or kilowatt hour – “kilowatt” refers to power usage and “hour” refers to time. Thus, what matters is not just how much power the appliance draws, but for how long it draws that power.

Let’s apply our imaginary scenario to a real world power bill. We’ll use the national average price for electricity – 12 cents per KWH – in all of our calculations. We’ll use three different sized dehumidifiers to demonstrate our point. Instead of using specific models, we’ll apply average data (average power usage and moisture removal rate for given size class) to three “archetypes”. We’ll also convert watts to kilowatts (371 watts = 0.371 kilowatts, for example) for these calculations to work.

Note: The average values used below were obtained from 2014 data. Since then we’ve tested and reviewed six more 70 pint dehumidifiers, two more 50 pint dehumidifiers, etc. Rest assured, the average data is still very similar. We just want to note here that the average power draw for dehumidifiers in the 70 pint size class is no longer exactly 612 watts. The average for the 50 pint size class is no longer exactly 454 watts, and so on and so forth.

Dehumidifier 1 >> 30 pint capacity

Power Draw >> 371 watts
Time Taken >> 24 hours

30pintenergycost

Dehumidifier 1 >> 50 pint capacity

Power Draw >> 454 watts
Time Taken >> 12 hours

50pintenergycost

Dehumidifier 1 >> 70 pint capacity

Power Draw >> 612 watts
Time Taken >> 7.2 hours

70pintenergycost
The calculations above speak for themselves. Yes, power draw is greater for larger capacity units. But larger capacity units draw that maximum power for a smaller amount of time. It should now be clear to you that 70 pint dehumidifiers are the most energy efficient. 50 pint dehumidifiers are slightly less efficient. And 30 pint units are the least energy efficient. Thus, we recommend that you stay within the 70 pint size class if energy efficiency is important to you.

As one final nail in the 30 and 50 pint dehumidifiers’ proverbial coffins, consider the fact that the calculations above are only for one hypothetical 24 hour period. If you plan on using your dehumidifier for weeks, months, even years, multiply the above differences in cost by 7, 31, 365, etc. Think about this difference in energy cost when you’re evaluating the retail price differences between 70 pint and 50 pint units or between 70 pint and 30 pint units.

Additional Important Note (added recently)

We want to add a special note about a detail that we didn’t consider as carefully as we should have in reviews for dehumidifiers we reviewed in earlier years. That is that moisture removal rate is also very important in assessing a particular dehumidifier’s overall energy efficiency. Why? It’s actually quite simple: Just as a 70 pint dehumidifier can be more energy efficient than a 50 pint dehumidifier because it needs to run for less time than a 50 pint dehumidifier, so also a particular 70 pint dehumidifier can be more energy efficient than another 70 pint dehumidifier because it takes less time to dehumidify a particular space (it has a faster moisture removal rate). It’s really that simple.

We made the mistake in reviews preceding this current year of making energy efficiency synonymous with power draw. Thus, 70 pint dehumidifiers which tested for lower power draw received higher energy efficiency ratings (scored out of 5) while those dehumidifiers which we tested for higher power draw were rated lower. We didn’t take into account moisture removal rate in evaluating a particular dehumidifier’s energy efficiency.

Rest assured, this mistake was corrected for all ratings and reviews since. We now assess a particular dehumidifier’s moisture removal rate in addition to its power draw in rating its energy efficiency. We suggest that you do the same: evaluate each dehumidifier’s power draw in the tables above IN ADDITION TO each dehumidifier’s moisture removal rate in the tables we made available here.

Comments

  1. Dan says

    If properly sized, how often should a dehumidifier be cycling/running? I have a 50pint unit in my basement, and it is almost always running. The basement does not have any standing water or dampness, just a little bit of moistness during the summer months (upstate NY).

    Would getting a second dehumidifier in the space allow them to cycle a bit more and not run 100% of the time?

    • Admin says

      If the dehumidifier is constantly running and never turning off then it is very likely undersized for the space you need to dehumidify. A second dehumidifier will definitely help but before you consider buying one, check that the current unit isn’t set to continuous mode. If it’s set to this mode it will constantly run no matter the humidity level in the space.

    • John says

      You might want to invest in a temperature and humidity gauge. Your space may be adequately dry but the humidistat on the unit may not be accurate or working. You may be perfectly fine at 60% while your unit is trying to get it down to 40/25/ or 0%!

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