Dehumidifier Buyer's Guide

Dehumidifier Buying Guide

Overview

Indoor humidity ranging from 30% to 50% is ideal for most home and offices (source: epa.gov). Activities like showering, bathing, cooking, dishwashing, and laundry contribute to increased humidity, especially when there is insufficient ventilation. Other sources include gas appliances such as water heaters, clothes dryers, stoves, ovens, and gas fireplaces. Moisture that condenses on water pipes may affect surrounding surfaces. Natural dampness in the soil beneath crawl spaces and basements will also add to interior moisture levels.

How can we tell if humidity is too high? Signs of excess humidity would be damp or musty smells, mold, mildew, peeling paint, moisture on the interior of windows during cold weather, and water stains on walls, ceilings or floors. Some smart thermostats display real-time humidity levels on the thermostat display or through the app. Humidity can also be measured with a hygrometer (available through many hardware stores). When humidity levels are too high, especially over 60%, both the occupants' health and the structure can be affected. Excess moisture may damage wood, sheetrock, and cabinetry, while warping around windows and doors can make them more difficult to open and close. Further, the likeihood of mold spores, mildew, and duct mites are greater, contributing to increased asthma, allergies, and respiratory issues.

Reducing indoor humidity can be accomplished in multiple ways. One is to ensure there is adequate exhaust ventilation in bathrooms, such as running a bathroom fan for at least 20 minutes after a shower has concluded. Some newer ENERGY STAR® bathroom exhaust fans have a built-in humidity sensor to ensure that the moisture is removed. Insulating water pipes will prevent condensation from forming on the pipes and dripping onto nearby surfaces.  Keeping roof gutters and downspouts clear, and landscaping in a way that directs water away from the foundation, will help as well. 

In many instances, however, even with comprehensive steps, dehumidification is needed. Portable dehumidifiers can be a highly effective way to remove excess moisture, using a fan to draw surrounding air across coils filled with refrigerant. Moisture in the air will condense on the refrigerant coils and then drain into a collection bucket or out through a hose, with the dry air exhausted into the surrounding space.  Some dehumidifiers only support gravity draining from an attached hose, while others have a pump to allow the water to be expelled upwards, or further away to the outside, into a sink or set tub, or to a floor drain. 

When selecting a portable dehumidifier, important factors to consider will be the moisture removal capacity of the dehumidifier, the type of refrigerant used in the dehumidifier, and the amount of electricity required to operate the dehumidifier.

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Moisture Removal Capacity

The moisture removal capacity is the amount of moisture that the dehumidifier can remove over the course of 24 hours. Typical capacities range from 20 pints per day to 50 pints per day, though there are models with higher daily capacities. In spaces with high humidity levels, a dehumidifier with a high daily capacity will perform better. If the location for the dehumidifier is not appropriate for use of a drain hose, meaning a collection bucket will be used, recognize that all dehumidifiers do not have the same size collection bucket. The larger the bucket, of course, the less often the bucket will need to be emptied. This is important, as when the bucket is full of water, the dehumidifier turns off. 

The table below offers general guidance relating to dehumidifier sizes and features.

Humidity Level	Suggested Dehumidifier Capacity	Comments
Low Excess Humidity: 55% to 75% (space feels slightly damp or has a musty odor)	20 to 30 pints per day	Selecting a model with a larger bucket will require less frequent emptying.
Moderate Excess Humidity 75% to 85% (intermittent dampness appears on surfaces)	30 to 50 pints per day	Selecting a model with a pump may be more convenient if there is a location to which water can be drained.
High Excess Humidity 85% or more (seasonal dampness is often present and/or wet areas form)	50 (or more) pints per day	Selecting a model with a pump is recommended to allow for continuous operation when needed.

 

When unsure, or in large spaces, select a model with a higher daily capacity. With some appliances oversizing can lead to increased energy consumption, but with a dehumidifier oversizing is less of an issue, because an energy efficient model with a higher daily capacity will run less often, while a model with low daily capacity could run continuously, and still not be able to keep up. 

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Refrigerant

When released into the atmosphere, the refrigerants used in appliances such as air conditioners, heat pumps, refrigerators, freezers, and dehumidifiers can be damaging to the environment. The refrigerant R-22, known as Freon, was commonly used through 2009. R-22 is a hydrochlorofluorocarbon (HCFC) chemical that contains chlorine, which was highly destructive to the ozone layer. In 2010 the United States Environmental Protection Agency banned manufacturers from using R-22 in certain new appliances, including dehumidifiers, necessitating the switch to different refrigerants. 

In many products the new refrigerant was R-410A, which is a hydrofluorocarbon (HFC) that does not contain chlorine and is, therefore, less impactful than R-22. R-410A is still, however, a greenhouse gas (GHG), which means its release into the environment contributes to global warming. The Intergovernmental Panel on Climate Change (IPCC) developed an index called Global Warming Potential (GWP) to allow the global warming impacts from various GHGs to be compared. As described by EPA "it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO₂). The larger the GWP, the more that a given gas warms the Earth compared to CO₂ over that time period" (source: epa.gov). The refrigerant R-410A has a 100-year GWP of 2,088.

Improvements are on the horizon once again. Some products are now beginning to use a new refrigerant, R-32, which has a 100-year GWP of 675. For a dehumidifier with 65 grams of refrigerant, this would mean that, if released into the atmosphere, the R-410A refrigerant would have a global warming impact equivalent to 299 pounds of carbon dioxide emissions, while the R-32 refrigerant would have an impact that was equivalent to 97 pounds of carbon dioxide emissions. Appliances with the R-32 refrigerant are not yet common, but as they become increasingly available, this will be an important feature to consider. 

This is a good opportunity to reinforce the importance of recycling appliances to avoid the impacts of the refrierants, regardless of which they may be. Only about 10% of the refrigerant used in an appliance is released into the environment through normal operation. The more substantial impact is at end of an appliance's life if the refrigerant escapes. When the refrigerant is collected properly, the contribution of the refrigerant to global warming is lessened as refrigerants can be converted into chemicals that do not contribute to warming (source: drawdown.org).

The Responsible Appliance Disposal (RAD) Web Site, managed by EPA, lists the refrigerant appliance recycling programs available in each state..

•  https://www.epa.gov/rad/find-rad-partner-programs

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Electricity Use

Because dehumidifiers often run for long periods of time it is important to select a dehumidifier designed to use electricity efficiently. A dehumidifier that has earned ENERGY STAR certification uses more efficient refrigeration coils, compressors, and fans to remove the same amount of moisture as a similarly sized conventional unit, but requires at least 13% less energy. The amount of electricity saved by using an ENERGY STAR certified dehumidifier instead of a conventional dehumidifier could power an ENERGY STAR certified refrigerator for nearly two months (source: epa.gov).

There are two metrics to consider when calculating the electricity that a dehumidifier will use to dehumidify a space. One is the dehumidifier's electricity consumption (wattage), and the other is the dehumidifier's efficiency (liters / kWh). The formula below will allow the electricity use to be calculated. 

• (liters to be removed / liters per kWh capacity) * (wattage / 1,000) = electricity consumption

We can use this formula to compare the electricity use of a conventional model to an ENERGY STAR certified model. In the United States, dehumidifiers with a 50-pint per day capacity must be able to extract 1.6 liters of water per kilowatt hour of electricity used (source: ecfr.gov). ENERGY STAR certified models must be able to extract at least 1.8 liters per kilowatt hour of electricity (source: epa.gov). If the dehumidfier were operating at full capacity for one week, 350 pints of water would have been removed, which is 118 liters. Therefore, to remove 118 liters of water....

CONVENTIONAL MODEL: wattage of 520 watts, removal capacity of 1.6 liters per kWh

• (118 / 1.6) * (520 / 1,000) = 38.3 kWh of electricity

ENERGY STAR MODEL: wattage of 520 watts, removal capacity of 1.8 liters per kWh

• (118 / 1.9) * (520 / 1,000) = 32.3 kWh of electricity

In this example, the ENERGY STAR dehumidifier will require 15.7% less electricity than would have been consumed by a conventional dehumidifier to extract the same amount of water. 

In November, 2023, the U.S. Department of Energy issued a proposed rulemaking update to the dehumidifier energy efficiency standards, increasing the minimum acceptable efficacy to 2.01 liters per kWh, delivering a net societal benefit of $3.75 billion factoring in lower operating costs, climate benefits, and health benefits (more info: federalregister.gov). 

POTENTIAL FUTURE STANDARD: wattage of 520 watts, removal capacity of 2.01 liters per kWh

• (118 / 2.01) * (520 / 1,000) = 30.5 kWh of electricity

If adopted, this improvement would represent a 20% reduction in electricity use relative to current conventional dehumidifiers. 

Actual annual electricity savings will vary based on numerous factors, but some energy-savings estimates are reflected in the Technical Resource Manuals listed below.

50 Pint Capacity

• 2023 Massachusetts TRM: 82.3 kWh annual savings (source: masssavedata.com)
• 2020 Mid-Atlantic TRM (ADM Associates): 90.0 kWh annual savings (source: cdn.entergy-neworleans.com)
• 2020 New Orleans TRM (Shelter Analytics): 92.0 kWh annual savings (source: neep.org)

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Summary

Excess indoor humidity can adversely impact both buildings and people. There are multiple ways to reduce excess moisture, including the use of a portable dehumidifier. When comparing dehumidifiers, choose a model that has a high enough moisture removal capacity to dry the space, if the dehumidifiers use different refrigerants select the model with the lower GWP, select the most energy efficient ENERGY STAR certified model available to minimize electricity use, and always recycle the exisiting dehumidifer if one is being replaced.

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Contributor: Philip Scarbro, March 22, 2024

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