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What Size Dehumidifier Do I Need?

Last updated November 25, 2021

This post may contain affiliate links.

Author avatar Danny Ashton

Danny as been writing about air purifiers for 10+ years. He is a major fan of home technology, which makes him the perfect person to test and evaluate products for HouseFresh

Homeowners know that water is enemy number one when it comes to protecting the house. Whether it’s a full-blown flood or everyday basement humidity, unmanaged moisture of all kinds will damage personal items, allow mold to grow, and eventually ruin your foundation.

Of all the ways to control moisture, a dehumidifier is by far the most practical. But if you haven’t bought a portable unit before, or if your needs have changed recently, you’re probably wondering, “What size dehumidifier do I need?”

The last thing anyone wants is a machine that uses too much power or, even worse, isn’t strong enough. If you want to make sure you get the right fit, we’ll show you the sizing factors to consider for your next dehumidifier.

Understanding Removal Capacity

Let’s start with the basics of finding the right portable dehumidifier. One of the most crucial specs is the capacity.

The capacity refers to how much moisture a dehumidifier will extract from the air every 24 hours. For example, if someone’s selling a “30-pint dehumidifier“, that means that it will cycle 30 pints of water a day.

Or at least it should be that simple but recently they changed the way this amount of water is calculated.

Changing Testing Standards

If you’re replacing a dehumidifier that you have had for at least a few years, it’s all too easy to accidentally buy one that’s too big for your space. Testing standards changed in 2020, and the capacity no longer reflects the same dehumidifying power.

So how is the capacity measured?

The U.S. Department of Energy sets the performance standards for dehumidifiers, which rate the capacity and energy efficiency of each model.

The capacity is set according to how much moisture a dehumidifier will remove over 24 hours under specific testing conditions. The DOE updated those conditions in 2020 along with their energy-testing metrics to provide more accurate information.

Under the old standard, which had been in use since 2012, dehumidifiers were tested at a room temperature of 80F with 60% humidity. The new standard tests machines at 65F, as this is closer to the average basement environment.

That temperature change is crucial to consider when looking at new dehumidifier capacities vs. old capacities. When measured in the same size room with similar humidity levels, a dehumidifier can extract more moisture as the temperature goes up.

With the change in testing conditions, the capacities of portable dehumidifiers dropped anywhere from 10-45 pints/day. On the small end of the spectrum, a model like the Honeywell 30-pint dehumidifier is now rated as a 20-pint dehumidifier. If you have a 90-pint unit, the new rating for the same model drops down to 55 pints/day.

What Size Dehumidifier Do I Need?

Now that we know what capacity means, it’s time to find the right one for your room. There are two essential variables of your space that will affect which dehumidifier to choose — the room size and the relative humidity.

The room size is the square footage of the total area you need to dehumidify. All things being equal, as your room gets bigger, your dehumidifier’s capacity needs to increase.

The same is true of the humidity levels in your space. The ideal relative humidity in the home is 30-50%. As the moisture levels increase, you’ll need a more powerful unit to bring the humidity down to a reasonable level that won’t allow mold to grow.

The Association of Home Appliance Manufacturers (AHAM) sets the recommended capacity based on size and humidity levels. Major manufacturers generally follow their standards, and they’ll tell you the optimal room size and dampness level that each of their models can manage.

Humidity Levels

The AHAM has several levels of relative humidity that will affect the capacity. On the low end, they have “moderate dampness,” where the relative humidity is around 50-60%. On the high end is “extremely wet,” meaning the room’s relative humidity is over 80%.

If you want the perfect dehumidifier for your space, it’s crucial to gauge the humidity as accurately as possible.

The best way to test the relative humidity levels of your space is with a humidity meter or hygrometer. These are small gauges you can set up in your room to monitor moisture levels and get notified when you need to turn on the dehumidifier. Many dehumidifiers have these gauges built-in, allowing them to cycle on and off automatically based on your humidity preferences.

If you don’t have a meter, you can feel out the conditions and make the best guess possible. There are four different levels of dampness:

  • A room is moderately damp if it only takes on a musty odor when it’s humid outside
  • A very damp room has a consistent mustiness, and small damp spots start to show up on the walls
  • A room is wet when it feels wet, and condensation sometimes forms on surfaces
  • A room is extremely wet when there is always water seepage in the walls or pooling on the floor

Once you know your room size and at least a rough idea of the humidity in your space, you can choose the right dehumidifier.

Adjusting for Different Conditions

Following the AHAM guidelines will tell you the correct capacity to effectively dehumidify your room, but other factors can determine the best model for you. 

If you live in a consistently humid climate, you may want to size up your dehumidifier. For example, if you have a 500 sq. ft. space with about 60% humidity, you want a 30-pint dehumidifier. But in a humid climate, it’s best to invest in a 40-pint unit.

Adding an extra 10 pints is a good rule of thumb for more humid spaces. In general, if you’re unsure of the right size or if the recommended size falls in a range, opt for a larger capacity. You can often run them on low, and with a built-in hygrometer, you can ensure it doesn’t overwork itself.

Find the Right Dehumidifier for You

It’s easy to buy the wrong size dehumidifier, but it’s also easy to buy the right size if you know what to look for. When you have to ask, “What size dehumidifier do I need?” follow the tips laid out here, and you’ll be sure to find the perfect unit for your needs every time.

Sizing is complicated enough, but there’s still more to think about when you need to find the best dehumidifiers available. Check out our dehumidifier page for more helpful insights, news, reviews, and advice.