How to choose a humidifier — Here's our knowledge from years of testing

Most people have heard of a dehumidifier to remove the moisture from the air but have perhaps not heard of humidifiers that do the opposite. Rather than removing moisture from the air, humidifiers add moisture. A study published in the Building and Environment journal found that portable ultrasonic humidifiers decreased the Total Volatile Organic Compounds (TVOCs) in the air. TVOCs are harmful to health, acting like pollutants. Not only this, but the same study found that the use of a portable ultrasonic humidifier also reduced the air temperature. These findings indicate that having a humidifier in your home can help reduce pollutants in the air while also helping to reduce the air temperature on a warmer day.

However, our expert, Melanie Carver, Chief Mission Officer at the Asthma and Allergy Foundation of America, suggests finding out if your room needs humidifying before purchasing one of the best humidifiers. She said, "A device known as a hygrometer (humidity sensor) can help you make this determination. It measures the relative humidity (RH) in your space. Ideally, your indoor space should be between 30-50% RH. The climate where you live, your home’s air ventilation and your indoor activities all affect your humidity levels."

But what should you look for in a humidifier? There are so many options out there that understanding all the terminology and functions can feel overwhelming. When choosing a humidifier for your home, there will be certain things to consider such as the room size, the space you have available to place the humidifier in, the style you'd prefer and the room you're placing it in, as, for example, if you're placing it in the bedroom you will want a quieter option. These are just a few of the things to consider.

While some of the best humidifiers may tick many boxes, the likelihood is that you'll have to compromise on something. Our advice is to consider what's most important to you and go from there. We've provided some more guidance below to help you understand what to consider when purchasing a humidifier.

We have years of experience in testing various humidifiers so we know what to look for. We will share with you our knowledge so you feel empowered to find the best humidifier for you. We'll take you through what to look for, step-by-step, so the next time you're searching, you feel confident. Let's see if we can get your home humidified in time for the warmer summer months...

Consider the room size

Some people may think that any humidifier can handle any space but this isn't the case. It's important to consider your room size when deciding which humidifier to purchase. Our expert, Melanie Carver, Chief Mission Officer at the Asthma and Allergy Foundation of America, explained the impact low humidity can have, "Low humidity can cause your skin to dry out as well as your eyes, nose and lips. It can result in a dry, sore throat as well as worsen eczema and asthma. If your humidity levels are below 30%, you can add moisture to the air by using a humidifier." She added, "Using an appropriate humidifier in your space can help to keep the humidity in your home at a healthy level."

Humidifiers came in various sizes from small to large. Small humidifiers, you guessed it, can handle smaller spaces, while the larger ones can effectively humidify larger rooms. Ensuring you get the right-sized humidifier for your space is key. If you end up with one that's too small for your space, it won't be able to provide the optimum humidity levels. This means you won't be receiving the benefits of having a humidifier — the air pollutants won't be reduced and the added moisture won't be enough to sustain that ideal humidity level as previously discussed by our expert, Melanie Carver.

On the other hand, if you purchase a large humidifier for a small room, you may find that the room becomes too humid. Too much humidity in a room or house can be an issue, causing damp and mold spores. Melanie warns of this complication, "High humidity causes the air to feel warmer than it actually is. This can cause you to overheat. It also encourages the growth of dust mites and mold (both of which can trigger asthma and allergies). They thrive in high humidity above 50%. If your indoor space is above 50%, you can reduce the humidity levels by improving your ventilation, using air conditioning or using a dehumidifier to remove moisture from the air. You obviously want to avoid causing any further issues, so we argue that selecting the right-sized humidifier for your space is paramount in your purchasing decision."

In order to understand what size humidifier is appropriate for your space, check the specifications. Most manufacturers make it very clear what size room their humidifier can work most effectively in.

What noise level is appropriate for you?

Once you're clear which room you're placing your humidifier in and you've got the right-sized humidifier for that space, next you should consider the noise level of the humidifier itself. This may be particularly important if, for example, you are placing it in the bedroom and want it to run overnight.

There are a couple of ways to work out what the noise levels of a humidifier may be like, even if the manufacturer doesn't mention this specifically in their description. In our best humidifiers guide, we tested some models with a decibel meter but we don't expect you to go round shops and do this. Generally speaking, ultrasonic humidifiers tend to be the quietest. This is because they use a high-frequency vibration to create the mist that's released into the air. These are a good option if you're looking for a humidifier that won't distract you or keep you awake.

You can also consider whether you want to have a warm or cool mist humidifier. Melanie Carver, our expert, offers some advice on this front: "There are different types of humidifiers that release water vapor or steam or mist into the air. For people with young children in the home, opt for a cool mist or ultrasonic option rather than a steam vaporizer to reduce the risk of burns."

Cool mist humidifiers use a fan to disperse the water into the air and are known as evaporative humidifiers. Conversely, warm mist humidifiers use a heating element to create steam that evaporates into the air. As cool mist humidifiers use a fan, this may make them slightly louder than warm mist humidifiers, so this is worth keeping in mind.

Ultimately, it is about whether or not you are distracted by noises in your home or if you find background noise calming. No humidifier is so unbearingly loud you won't be able to deal with it, but saying that, we all have our own tolerances to noise. If you're sensitive to background noises or hums, we suggest going for an ultrasonic humidifier for minimal noise disturbance.

And what about maintenance?

Many people may not think that humidifiers require maintenance but they do and this is something to bear in mind if you're thinking of buying one. There are many ways you can ensure the smooth running and longevity of your humidifier. A regular cleaning will do wonders, while others suggest using only distilled or soft water. This is because the type of water in your home can impact the lifespan of your humidifier. For example, hard water can contribute to mineral buildup. This buildup can make your humidifier less effective due to blockages in water flow, with it even causing damage to the humidifier's components. On the other hand, soft water is much less likely to have these effects, with soft or distilled water being recommended over hard water. Of course, if you live in a hard water area, you will have to rely on distilled water if you want to keep your humidifier in top condition.

Our expert, Melanie Carver, offers further suggestions for an optimal clean: "Clean your device per the manufacturer’s instructions. If you don’t have the manufacturer’s recommendations, the Environmental Protection Agency (EPA) recommends a 3% hydrogen peroxide solution may be useful for cleaning humidifiers. A scrubbing brush can be helpful to reach small areas or corners." She added, "The Asthma and Allergy Foundation of America also recommends just plain soap and water for the collection tank/reservoir parts of the machines. Do a thorough rinse and dry whenever cleaning with soap or any other cleaning solution."

Furthermore, it is recommended that you change the water daily and keep on top of any mineral buildup by performing a thorough clean every few days. Our expert, Melanie Carver, explained there were signs to watch for that will help you identify when your humidifier is due a clean, "If you see build-up or discoloration on any part of the humidifier — water tank, reservoir, base, etc. that is a sign it needs cleaning and could indicate mold growth." Humidifiers also have filters that will need changing as per the manufacturer's guidance.

So, as you can see, having a humidifier working effectively in your home isn't a case of plugging it in, filling the tank and leaving it. To get the most out of these devices, it's important to consider how much time you can give towards cleaning and maintaining them to ensure their longevity.

Consider any extra features

Now we've covered selecting the right-sized humidifier for your space, the potential noise levels to be aware of and how to maintain your new investment, we move on to the features of humidifiers. While the basics of what they do are similar (adding moisture to the air through various means, be that ultrasonic, fan-based or through a heating element), there are differences in the extra features that they offer.

However, there are some key features to look for. Melanie Carver, our expert, explained, "The most important features include automatic shut-off and a humidity sensor that measures and displays your room’s relative humidity so you can keep the space within 30-50% RH."

The automatic shut-off feature is a good idea, especially if you want to leave the humidifier running while you've popped out. When the tank is running low, if a humidifier has this function, it will shut off. This is a safety feature that gives peace of mind. However, the runtimes on humidifiers vary dramatically, with some lasting only 60 minutes and others 50 hours or more. Runtimes may impact whether you think an automatic shut-off feature is essential, as if it only runs for a total of an hour, you may be around within that time to shut it off yourself. Automatic shut-offs can be more useful for those who go to work all day and would prefer to leave the humidifier running while they are out. There are other differences in features such as the addition of lights. You will need to consider the placement of your humidifier and whether, for example, lights will be a nice addition or just cause irritation as they may light the bedroom up at night.

This is not an exhaustive list of features, with some, such as the PureGuardian H950AR humidifier, having a separate oil tank to allow you to infuse the moisture with essential oils. However, our expert, Melanie Carver, advised that infusing the moisture with fragrances may not be a helpful feature for those with asthma: "Some humidifiers have a feature for you to add fragrances. Fragrances are a common asthma trigger, and so the Asthma and Allergy Foundation of America does not recommend adding fragrances to any air care device."

We recommend you look at the product details closely to get an understanding of what else the humidifier offers to see if it suits your needs.

How much do they cost to run?

One of the big considerations for you may be the cost of running a humidifier. Luckily, the cost of running a humidifier is generally low, with them costing less than running an air conditioning unit, for example. As with any electrical appliance, the running costs will depend on how often you use it and the rates of your electricity.

Our expert, Melanie Carver, offers further advice, "The power consumption of humidifiers is going to be dependent on the type of humidifier you are using and how often it runs. Ultrasonic humidifiers tend to consume less energy than cool mist or steam vaporizers. The EPA’s Energy Star certification has been a helpful resource for consumers to identify appliances that use less energy. But the Energy Star program does not certify humidifiers."

Our expert

Melanie Carver

Melanie Carver became Chief Mission Officer for Asthma and Allergy Foundation of America in 2020.  She leads the organization’s strategy, community services, marketing and communications, education, and grassroots advocacy. Under Carver’s leadership, the organization expanded its work in promoting health equity. She is co-author of the Foundation’s landmark Asthma Disparities in America report and provided strategic leadership in the launch of the organization’s Health Equity Advancement and Leadership program. Carver has also expanded the organization’s library of education programs for patients, caregivers, and allied health professionals. She is a staunch proponent for health literacy and health equity. Carver has raised greater awareness of AAFA’s joint venture, the asthma & allergy friendly® Certification Program, and how it addresses indoor air quality and allergen exposure. She leads the organization’s support of asthma home visits and assessments as well as climate readiness and resilience.