Humidifiers and dehumidifiers are useful appliances that help maintain optimal humidity in your home. For most people, a relative humidity level between 40–50% in the summer and 30–50% in the winter is ideal. If the humidity drops below that level, the dry air can irritate your nose and throat, and dry out your skin, eyes and lips. Dry air may also shrink wood, damaging furniture, floors, and walls. Additionally, low humidity can make your home feel colder, especially in the winter. A humidifier counteracts these effects, adding moisture to the air to boost the humidity back to comfortable levels.

A dehumidifier extracts moisture from the air to reduce the humidity level. High humidity may spur mold and mildew growth, which can exacerbate allergies and rot your walls. High humidity can also make the air feel much warmer, especially during the summer. Substantial condensation inside your windows is a good indication humidity levels in your house are too high. 

This buying guide explains the factors to consider when selecting a humidifier or dehumidifier so you can feel confident you’re selecting the right model for your needs.

Tabletop Humidifiers – Also called portable humidifiers, tabletop units are ideal for humidifying a single room. The typical design plugs directly into a wall and pulls water from a refillable tank. Tabletop units are lightweight, making it very simple to move them between rooms. Small tabletop units are sometimes called compact humidifiers.

Tower Humidifiers – If you prefer to set a humidifier on the floor instead of a table, consider a tower design. These are perfect for humidifying a medium-size room. Some tower models need refilling less frequently than tabletop units.

Console Humidifiers – Like tabletop and tower humidifiers, console units are self-contained systems with refillable tanks, but they offer considerably more power. Console units are designed to humidify several rooms at a time, and they generally have larger tanks, which you don’t have to refill as often. Consoles are bigger and heavier than tabletop and tower models, but can still be moved between rooms.

Whole-House Humidifiers – Also known as in-duct or online humidifiers, whole-house units introduce moisture directly into a forced air heating system. In the typical design, air blows through a wet wick, into a duct leading from the furnace. When the forced air system is running, it carries the moist air to every room in the house. Most whole-house humidifiers connect directly to the household water supply, which means you never need to refill them. They also have the lowest energy demands of the three humidifier sizes. Whole-house units require professional installation and will only work with a forced air heating system.

Humidifier Designs 
There are four common humidifier designs, each with their own distinct benefits:

Warm Mist Humidifiers – Also known as steam humidifiers, these models work like a tea kettle. A heating element boils water from a refillable tank or the household water supply, generating steam that humidifies the surrounding air. Like evaporative humidifiers, warm mist humidifiers remove impurities from the water, producing clean saturated air. One key benefit of this design, especially during the winter, is the steam helps keep rooms warm. Since they don’t include a fan, warm mist humidifiers are very quiet. Tabletop and console models require you to refill the water tank periodically, but there’s no wick to replace. However, it may be necessary to clean the unit regularly, as impurities from the water can build up in the tank.  

Vaporizers – Small, low-output warm mist humidifiers are called vaporizers. These units have a built-in water reservoir, rather than a removable tank.

Cool Mist Impeller – In this tabletop design, a spinning disc generates a fine mist of cool water. Like ultrasonic humidifiers, impeller models are quiet and don’t use much power. They do need to be refilled, but there aren’t any filters to replace. Since impeller models don’t remove water impurities, it’s best to fill them with distilled water and clean the tanks regularly.

Humidifier Ratings
When comparing humidifier models, consider these common power and performance ratings:    

• Bucket size – The size of the water collection bucket. A dehumidifier with a larger bucket can run for a longer period of time before you need to empty it.
  
  

• Adjustable Humidistat – A system that turns the dehumidifier on and off automatically to maintain a preset humidity level

• Digital Display – A display of current relative humidity levels and settings

• Automatic Shut-Off – A standard feature that shuts off the dehumidifier when the tank is full

• Drain Hose Connection – A connection that allows you to bypass the bucket in a portable dehumidifier and empty water into a hose leading to a drain

• Automatic Defrost – A system that saves energy by automatically shutting off the unit if frost forms on the coils, preventing proper operation

• Multi-Speed Fan – A type of fan that runs at slower speeds in less humid conditions, reducing noise and energy consumption

• Wheels or casters – A standard feature that makes it easier to move portable dehumidifiers from room to room

• Built-in Pump – A system that allows you to run the drain hose up to a window, sink or elevated drain

• Safety Listing: A guarantee that an independent testing agency, such as Underwriters Laboratories (UL mark), Intertek (ETL mark) or the Canadian Standards Association (CSA mark) has ensured the humidifier is safe for its rated use

• ENERGY STAR ® – A label indicating the product meets stringent energy efficiency guidelines outlined by the U.S. Department of Energy and the Environmental Protection Agency