Understand your ideal relative humidity level

In most cases, the ideal relative humidity level for your home will be between 40% and 50%. 

In this range, you can expect a comfortable home, improved respiratory breathing, and also discourage bacteria and mold growth.

Step 1: The different types of humidifiers available

Type of humidifier by principle of operation

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Comparing evaporative, ultrasonic, and vaporizing humidifiers

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Type of humidifier by mist temperature

Some models, such as the Levoit LV600HH, offer the option to choose between cold and warm mist. This versatility is nice for those who use their humidifiers year-round to meet their specific needs. 

However, I find that dedicated devices perform much better for specific needs. Never purchase a dual mist machine for your children’s room, as curious hands could change the settings.

Step 2: Size the humidifier properly

Three different size categories

Related article: Furnace humidifiers reviewed

The coverage area is often mentioned

For all of the size categories, the manufacturer typically lists the square footage of the area in which the humidifier can cover.

It’s very important to match the coverage area with the right size humidifier. A humidifier too small for the space will fail to properly humidify the air. 

Keeping humidity levels between 40% and 50% helps avoid over-humidification, which can lead to condensation on windows, musty odors, or mold growth on walls and fabrics.

Proper placement is key to good performance

Where you place your humidifier matters just as much as which one you buy.

In smaller rooms, keep the unit at least one foot away from walls, curtains, and furniture so mist can circulate freely without causing damp spots. In larger spaces, aim for a central location to ensure even humidity levels throughout the room.

Ultrasonic humidifiers perform best on a raised, waterproof surface like a nightstand or table, which helps the fine mist spread evenly.

Evaporative humidifiers need good airflow, so keep them in an open area where the fan can draw in and release air efficiently.

What is the moisture output per day?

Moisture output per day is the amount of water a humidifier can disperse into the environment within a 24-hour period. Sometimes moisture output is listed as “capacity per day” and this can be displayed in gallons or liters. 

Here’s a quick look at how several top humidifiers compare in output. Keep in mind that smaller units may need to be refilled in order to achieve their maximum daily output.

Models with a built-in humidistat will turn on and off as required by the current relative humidity percentage, and therefore these models do not typically list the moisture output.

Whole house humidifiers that are connected to a water line will list the maximum moisture output available to the unit.

Step 3: Consider the fill type

All humidifiers require water to perform properly, and smaller units may need to be filled a couple of times per day to reach the desired output. Before purchasing, make note of whether your dehumidifier type requires distilled water or if it can use tap.

There are four ways of filling your humidifier:

ACLab Note:

Some humidifiers, such as evaporative console humidifiers and whole home units, can use regular water from your home tap. However, it’s very important to use only distilled water in ultrasonic units, as these have the highest potential to spew mineral particles into the air (known as white dust).

Step 4: Tank size and runtime

Furnace humidifiers are attached directly to a water line within your home, and therefore, you don’t have to think about refilling their tank to get the most out of them. 

The downside here is that you’ll need to ensure your water bills don’t skyrocket. AprilAire suggests that their whole home humidifiers use about 1-3 gallon of water per hour.

For all other portable humidifiers, the runtime will be directly proportional to the tank size and output. 

Models with a built-in humidistat will stop running as the desired relative humidity is reached, and start again as necessary. This can make it a bit tricky to estimate how often the tank will need to be filled. 

Most humidifier manufacturers note both a tank size and a runtime, assuming that the model would be running at 100% for the entire duration. 

Here’s an example of how some humidifiers match up:

You can see that the impact of tank size on runtime in humidifiers generally follows a direct relationship: a larger tank allows the humidifier to run longer without needing a refill, assuming the device operates at a constant output rate. 

However, the relationship isn’t always linear due to factors like:

Step 5: Keep the noise levels in mind

Noise level is a key factor, especially if you plan to use it in a bedroom, nursery, or workspace. 

Some humidifiers, particularly ultrasonic models, operate quietly, making them ideal for overnight use or quiet environments. Evaporative models, on the other hand, may produce a light fan noise that varies by brand and model.

Consider Your Environment

Noise Ratings

Many manufacturers list decibel (dB) ratings for their humidifiers, but they are not required to. As a quick guide:

Step 6: Important features to consider

A unit with an auto humidistat

It’s important to know whether the unit you are purchasing has a hygrometer or a humidistat. While a hygrometer can measure humidity levels and show you what they are, a model with a humidistat can control the humidity to the desired level.

Auto shut-off

Auto shut-off is an important feature to look for, but it can have one of two functions:

Smart WiFi controls

Some newer humidifier models, such as the Dyson PH03, have the option to be controlled remotely via an App. 

This feature's benefit is that it can help you understand your humidifier usage and even create a custom schedule to get the most out of your device.

Different operating speeds and modes

Look for models with various operating functions, such as:

Step 7: Consider how easy it is to clean

All humidifiers require ongoing care and maintenance to prevent them from becoming a petri dish of bacteria and disease.

ACLab Note:

When humidifier season ends, always empty the tank, let all parts dry completely, and store the unit in a cool, dry place to prevent mold and mineral buildup. Before storing, give it one final deep clean and replace any worn filters or pads so it’s ready to go next season.

Step 8: Do You Need a Combo Device? (Optional)

Some humidifiers are 2-in-1 devices, which can be especially useful if you live in a tight space, such as an apartment.

Humidifier with essential oil tray

Models like the PureGuardian H950AR have a special tray in which you can add a few drops of your favorite essential oils to diffuse. 

It’s important to never put essential oils into humidifier water unless the manufacturer specifically mentions its use.

Related article: Humidifier versus diffuser

Humidifier with air purifier combo

Though less common and more expensive, some humidifiers also have an air purifying function. This is particularly useful if your primary humidifier use is due to seasonal sickness. 

Related article: Humidifier versus air purifier

Step 9: How much do you want to spend?

When purchasing a humidifier, it’s important to think about both the upfront cost of the unit and the ongoing costs of water and maintenance needs. In general, the more features your humidifier has, the more expensive it will be. Here is a general guide to humidifier pricing: