If you live in an area prone to high humidity or if you just have too much dampness in your basement, a dehumidifier can help reduce the risk of mold and mildew and even protect the structure of your home when moisture threatens to damage the foundation. Any owner of a newer home should consider purchasing a dehumidifier—as homes become more energy efficient and airtight, they’re getting too good at keeping moisture in and can develop mold quickly if humidity levels aren’t controlled. What should you look for when you buy yours? Pronto’s Dehumidifier Buying Guide takes you through everything you need to consider before making your purchase.
A rule of thumb when considering dehumidifier capacity in square footage: factor 75% of the manufacturer’s rating for square footage as a truer means of calculating what you need. Capacity is also measured in pints per day. For residential use, 70 pints or less is what most need.
Storage tanks range in size from as small as 10 ounces to over 40 pints. If you’re running a high capacity dehumidifier with a small tank, get a drainage hose for convenience. If your drain is located far from the dehumidifier, be sure to shop for a model that has built in pump convenience.
While these dehumidifiers are best for high-humidity environments, be keenly aware of the low end of your dehumidifier’s temperature range and shop for models that can handle your temperature range to prevent freezing that disables or damages the unit.
These humidifiers are most useful in low-humidity situations and may be more effective at lower temperatures than refrigerative dehumidifiers, but work best in concert with refrigerative dehumidifiers to reduce humidity quickly, or combat a high humidity situation.
Features you don’t want to go without are anti-freeze functions and hose hookups to extend the life of the unit and make it easy to use. Other features that are nice to have include adjustable humidistat, auto-shutoff functions, and auto-restart if service should be interrupted. Electrical controls are easier to use than mechanical.
Relative humidity is the term for the ratio of the amount of water currently in the air to the amount of water that the air is capable of holding. The desired relative humidity for indoor air is between 30-50%.
A hygrometer is an instrument that can measure the amount of relative humidity in the air. Mechanical models can be purchased for as low as $10, while digital models generally range in price from $30-50.
A humidistat is a hygrometer that is built into a dehumidifier. The humidistat can measure the relative humidity, and many models can be programmed to turn on or off automatically when a desired humidity level is reached.
A dessicant is a material that naturally attracts water vapor. Often calcium oxide or silica gel, it functions as a drying agent by soaking up water vapor, which is then evaporated.
Mechanical or Refrigerative Dehumidifiers operate on the principal of trapping the air, cooling it, and then dripping the condensation into the storage tank. This is the more common style of dehumidifier, and is most useful in high-humidity situation, but it’s best suited to warmer climates or seasonal use in other climates. Mechanical dehumidifiers lose prime function capability as the air temperature drops and if the cooled air nears the freezing point, it can disable or even break the dehumidifier. Check the manufacturer specs to determine the functional temperature range for your dehumidifier. Some dehumidifiers will only function down to 65 degrees Fahrenheit, whereas other dehumidifiers advertise that they may work all the way down to 38 degrees Fahrenheit.
Less common than refrigerative dehumidifiers, dessicant dehumidifiers use a chemical agent to reduce moisture in the air. They work well in low-humidity situations, but they are not as useful as refrigerant dehumidifiers in high-humidity applications. A benefit of a dessicant dehumidifier is that it is less prone to freezing problems than a refrigerant dehumidifier. If you need a dehumidifier to function well in low humidity levels or low temperatures, a dessicant dehumidifier is the better choice. However, due to the high energy costs of running this type of dehumidifier, it is really only useful in those circumstances, or in tandem with a refrigerative dehumidifier if you need to lower humidity levels drastically or quickly.
The larger a dehumidifier’s capacity, the more quickly it does its job. Unlike other small appliances, you won’t suffer if you buy ‘too much’ dehumidifier. In fact, if your dehumidifier isn’t large enough for the area you’re trying to treat, it may run constantly without ever actually reaching your target relative humidity level. And you won’t notice a significant increase in energy cost with a larger dehumidifier either. Better models allow you to set the desired humidity level and feature an auto-shutoff when the relative humidity reaches the desired level.
How do you evaluate capacity when shopping? There are two capacity measurements you’ll run into when looking at dehumidifiers. Some manufacturers loosely determine capacity merely by square foot rating or the dehumidifier’s ability to lower the relative humidity level. Unfortunately, this method of measurement doesn’t accurately measure the ability to achieve target humidity levels within a certain square footage. Instead, follow this rule: factor in 75% of the manufacturer’s square foot rating when deciding on your unit. So if you’re looking at a dehumidifier that says it can treat 1000 sq ft, it’s better to assume that it can reasonably handle around 750 sq ft.
The other, more accurate way the capacity of a dehumidifier can be measured is in the number of pints of moisture that it can remove from the air within 24 hours. Dehumidifier capacities typically range from 25-120 pints per day. Most portable dehumidifiers have a capacity of 70 pints or less, whereas industrial dehumidifiers can remove up to 125 pints in a 24-hour period. A 25-pint dehumidifier is most effective in small areas like storage spaces or an RV. A 50-pint dehumidifier can handle most spaces with above average relative humidity levels, but for maximum moisture removal in high-humidity basements (or tropical climates), 70-pint dehumidifies prove to be the most efficient.
In addition to figuring the capacity of the dehumidifier, you have to consider the storage tank or drainage hose. Depending on the size of the dehumidifier, storage tanks can range from 10 ounces to over 40 pints. But if you have a 40 pint tank in a 75 pint dehumidifier, the tank will get full and the dehumidifier will shut off automatically without reaching its full dehumidifying capacity. If your relative humidity levels are high, or if your dehumidifier is in a basement or crawl space, changing a storage tank daily is not a good solution. This is when it’s useful to have a dehumidifier with a drainage hose, and possibly even a pump. A drainage hose uses gravity to allow water to empty from the lowest point of the dehumidifier tank, while a pump can be utilized to force the water through the hose.
The simple hose by itself, relying on gravity to drain the tank, is fine if your dehumidifier is elevated above a drainage outlet. If you need to carry the water some distance from the dehumidifier to drain, such as out of a crawl space or into a basement sump pump, you may need a pump to physically force the water through the house and out to your drainage outlet. Most dehumidifiers come with the option of using either a storage tank or a hose. If your needs require a pump, be sure to look for a model that offers this convenience.
There are many things that can cause a dehumidifier to stop working properly, so it’s important to look for standard features that address these common problems. Most important, look for a dehumidifier with defrost or anti-freeze functions. If your dehumidifier freezes, it can actually damage or break the dehumidifier and will stop the dehumidifying process. For added convenience and energy conservation, look for adjustable humidity controls with an auto-shutoff. In the event of removing and changing the storage tank, or in case of electrical failure, some models feature an auto-restart option which will resume interrupted service automatically. Electrical controls are often easier to use than mechanical controls, so make sure you’re comfortable with the controls available when considering what model to buy.