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What Size Dehumidifier Do I Need and What Other Factors Affect Relative Humidity?

Dehumidifiers are a home appliance that reduces the humidity and moisture in the air. This thing has become popular because of the recent drastic changes in the weather and the climate.

People have been getting different kinds of dehumidifiers, and have been ranting how they have not been effective. Before buying their units, they must have missed asking the question “what size dehumidifier do I need?”

There are a lot of sicknesses these days that are attributed to high humidity because it creates a damp environment where bacteria, molds, mildew, and even harmful insects thrive. A home dehumidifier will only be effective in creating healthier environment if it is the right size for the room or space that the user wants to dehumidify.

There are a lot of brands and models of dehumidifiers these days, so choosing the best one is quite a challenge. There are portable dehumidifiers, as well as big dehumidifiers with caster wheels.

There are those with removable water tank, whilst other dehumidifiers come with a hose and pump for continuous disposal of collected moisture from the air. Some have a compressor, while most have adapted the Peltier technology.

However, the most important thing to decide on is the size of the dehumidifier that will effectively keep the moisture in the home within the healthy range. Likewise, it is equally important to consider other factors that could affect the performance of the dehumidifier as will be discussed below.

AHAM Standards

The acronym AHAM stands for Association of Home Appliance Manufacturers. This organization has come up with a general guide on how to choose the dehumidifier based on the size that will work best within a specific area.

Dehumidifiers are categorized based on their capacity to reduce moisture in the air within a day, specifically within 24 hours, and not on their actual physical size. Bigger dehumidifiers do not always have greater capacity. The size of a dehumidifier does not always have a positive relationship with its capacity.

The sizing table from AHAM takes into consideration not only the space that the dehumidifier will cover but also the condition of the area with regard to dampness and odor. Below is a complete list:

  • 30-39 pints capacity – 300 sq. ft. area with slight to moderate dampness (50-70% relative humidity)
  • 40-49 pints capacity – 300 sq. ft. area that is very damp or wet (70-100% relative humidity), 500 sq. ft. with slight to moderate dampness (50-70% relative humidity)
  • 50-59 pints capacity – 500 sq. ft. area that is very damp or wet (70-100% relative humidity), 700 sq. ft. with slight to moderate dampness (50-70% relative humidity)
  • 60-69 pints capacity – 700 sq. ft. area that is very damp or wet (70-100% relative humidity), 1000 sq. ft. with slight to moderate dampness (50-70% relative humidity)
  • 70-89 pints capacity – 1000 sq. ft. area that is very damp or wet (70-100% relative humidity), 1500 sq. ft. with slight to moderate dampness (50-70% relative humidity)
  • 90+ pints capacity – 1500 sq. ft. area that is very damp or wet (70-100% relative humidity)

What is Relative Humidity or RH?

The term “relative humidity” is always used when talking about dehumidifiers. However, what really is relative humidity?

This term is what is usually used when weather reporters talk about the amount of moisture in the air relative to the amount of moisture the air can actually hold.

Generally, warm air can hold more water than cool air. Relative humidity increases when the warm air that holds the specific amount of moisture or water becomes cool.

For instance, the basement during a summer day could hold so much, so when night time comes, the relative humidity in the basement increases since the air that has become cooler cannot hold much of the moisture the hot air has retained. Learn more about how temperature affects humidity in your home.

Different Sizes of Dehumidifier

Relative humidity is the main basis for finding the perfect size of dehumidifier per section or area in the home. Before purchasing and deciding on the size of the dehumidifier to purchasethe buyer should not only measure the area but also observe its humidity and the pattern of it having warm or cool air.

For instance, a bathroom that uses hot water will have elevated relative humidity once a person finished taking a shower. If there are a lot of people using the same bathroom, the relative humidity of that bathroom changes from high to low frequencies. However, note that when no one is using the hot shower, then the relative humidity could be at normal levels.

Other Factors to Consider When Answering “What Size Dehumidifier Do I Need?”

After finding out the specific size of the area where the dehumidifier will be used, and after having identified how damp it is, and how often and how long it has relative humidity, it also pays to add five to 10 pints more in the capacity based on this guide:

Add five pints for each category—if more than one person will inhabit the area at one time, if there are relatively more than normal number of doors and windows in the area, and if there’s a washer or dryer close to the area
Add 10 pints if the home is located in a state or area that has a humid climate

What to Expect from a Dehumidifier?

When buying a home dehumidifier, users should never think that if it says it can gather up to 30 pints of moisture in 24 hours, it will really do that. What people can see in the advertisements are what the dehumidifier can do in perfect environments, usually when the relative humidity is 80% above and the room temperature is 86 degrees Fahrenheit.

A lot of buyers have been complaining that their dehumidifier is not doing its job since the tank has not been filled even though it has been on for more than three days in an area that “seems” to have high humidity, i.e., there’s moist in the glass windows, or it really smells musty.

They are also confident that they are using the right size based on the criteria aforementioned to answer the question what size dehumidifier do I need.

The moisture can appear although the RH is less than 80%. The molds and mildews could have already been causing the musty smell in the basement before the dehumidifier was put in its place. The bad odor does not necessarily mean that the relative humidity is higher than 80% while the dehumidifier was running.

Aside from making sure that the dehumidifier’s capacity will match the size of the area and its other characteristics, one way to make sure that the appliance is working properly is by monitoring the relative humidity and temperature in the room 24/7 and taking note if it is gathering moisture or not.

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