Dehumidifier vs humidifier

Two opposite jobs

A dehumidifier pulls moisture out of the air. Room air crosses a cold coil, and the vapor in it condenses into a bucket or a drain. A humidifier does the reverse: it adds moisture, as vapor or mist.

The EPA gives both machines the same target. Indoors, it advises keeping humidity below 60%, and ideally between 30 and 50%. For humidifiers, it adds a ceiling: don’t go above 50%, since higher levels may encourage the growth of biological organisms in the home.

Which one you need

Measure first. A hygrometer, which the EPA notes you can buy at a hardware store, gives the relative humidity of the room.

• Above 50%

  A dehumidifier

  Also with condensation on the windows, or a musty basement.

• 30 to 50%

  Neither

  The room is in the EPA’s range.

• Below 30%

  A humidifier

  Set no higher than 50%.

For a dehumidifier, size comes from the ENERGY STAR® table, by floor area and dampness. The EPA lists 482 certified models sold in the United States, from small room units to whole-house systems.

Both in one home

It happens, at different times or in different rooms.

In winter, keep the target lower. ENERGY STAR says that in colder climates, during the heating season, humidity should stay between 30 and 40% to keep condensation off the windows. Two machines aimed at the same room would only work against each other.

Looking after each one

Both have a tank or a bucket, so both need cleaning. For portable humidifiers, the EPA’s advice is specific: empty the tank, wipe the surfaces dry, and refill it daily. Clean it every third day, and use water low in minerals, such as distilled water.

For a dehumidifier, the bucket is the part to watch: empty it often, and clean it with detergent and water if spots appear. A hose to a floor drain keeps the bucket empty.

Sources

Every figure and quote on this page comes from these, each with the date we read it.