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Friday, April 19, 2024

When to Use an Air Purifier, a Humidifier, or a Dehumidifier

Our homes are our sanctuaries—a fact that became clear to a lot of people this past year when they suddenly had to spend all their time there. But your indoor air might be dirtier than you think, and that could be making it uncomfortable at home, and potentially even make you sick.

There are a few things you can do to help and devices you can buy, like an air purifier, a dehumidifier, and a humidifier. But they aren't cheap, so you don't need to spend the money on anything if you aren't already struggling with your indoor air quality. These are potential tools, not necessities. While their names are self-explanatory, it's not as easy to figure out when each one is actually needed in your home. We talked to experts, read research reports, and tested some products. Below is what we found, and what we advise.

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What’s the Problem With Indoor Air?

The air, unfortunately, is filthy. Generally it's full of dust; pet dander; outdoor pollutants, which could include wildfire smoke depending on where you live; formaldehyde, which can come from wood furniture; and particulate matter. Your indoor air can also include a number of volatile organic compounds. However, VOCs overall aren't a health issue, only specific ones, and those will vary from house to house.

The World Health Organization estimates that nine out of 10 people are exposed to air pollution that increases their risk for several diseases, including stroke, heart disease, and cancer.

dust particles floating in a living room with plants, couch and a brick wall

Room to Breathe: My Quest to Clean Up My Home's Filthy Air

Poor indoor air quality causes serious health issues. Things can be improved with determination to sniff out the cause of the problem—and some pricey hardware.

By Lisa Wood Shapiro

“There are many pollutants that can be found in someone's home depending on many factors such as geographic location, or the age of the home and the building materials used,” says Joe Heaney, president of Lotus Biosecurity, a company in the indoor-air-quality-improvement business. “If you have a home with a wood-burning stove or fireplace, those are likely to introduce particulate matter into your indoor air, which can cause a range of respiratory symptoms and illnesses. Mold, dust, or pet hair can be a source of allergies, and pathogens (while not pollutants) introduced to the house by friends and neighbors may cause illness.”

On a basic level, when the air inside is stuffy, too dry, or too humid, it affects the way you feel, worsening cold and allergy symptoms, drying out your sinuses and skin, and even attributing to mold growth. But it can get much worse than that.

“Poor indoor air quality can affect even the healthiest lungs,” says Kenneth Mendez, president of the Asthma and Allergy Foundation of America. “Pollutants can irritate the eyes, nose, and throat, and cause headaches, dizziness, and fatigue. This can trigger allergy symptoms including chest tightness, coughing, wheezing, sneezing, shortness of breath, and even asthma attacks.”

See the testing section below on how to monitor the air in your home, but before testing your air or purchasing anything, try to first tackle some of the biggest causes of dirty air. “We like to focus on the technologies, but the process is much more important," says Jeffrey Siegel, a researcher at the University of Toronto who studies indoor air quality, filtration, and air cleaning. These are the steps he recommends:

  1. Source control: Understand the sources of polluted air and try to correct them. Some things we can't control, but others we can, like using a range hood fan while cooking, smoking outside, opening windows while vacuuming, and avoiding being in freshly painted areas.
  2. Proper ventilation: Older houses typically have poor ventilation, so you'll need fans or open windows to get air flowing. The CDC has useful tips on improving ventilation.
  3. Air cleaning: We can't keep pollutant sources down completely—we have pets, dust is inevitable, and not all landlords are created equally in terms of providing proper home equipment. This is when adding an air purifier, or multiple depending on the size of your space, will come in handy.
  4. Keep it dry: Indoor moisture problems can cause many issues, including mold. If you notice leaks or mildewy basements, fix the root of the problem as soon as possible. If you can't, consider a dehumidifier (but that's a Band-aid, not a fix).

How to Test Your Air

Air quality testers offer an easy way to learn about your home's air. Siegel says these devices are helpful for users to see relative responses to their actions. For example, the number of particles in the air goes up while you're vacuuming, but if you open the window while you clean, it should go down. The same goes for cooking with a range hood on or off. An indoor air quality device should show you this in real time, which can teach you better habits. None are perfect, and none can tell you everything lurking in the air. ("It’s actually a very long list," Siegel says of the number of pollutants around us. “We don't actually know all of them.”) But such devices are a good first step.

For tracking levels of formaldehyde (CH2O), total volatile organic compounds (TVOC), and the general air quality index, you can try the Temtop M10 ($90). This measures particulate matter that is 2.5 micrometers or smaller, like wildfire smoke.1 Unfortunately, the M10 doesn't measure CO2 or humidity. The inexpensive ThermoPro TP55 ($15) gives you just humidity info. 

We haven't tried the Awair AQM8002A ($149), but we've liked this brand's other products in the past, and this particular model measures a few important factors that the above monitors don't, including CO2. If budget is of no concern and you want to measure everything, I loved using the uHoo smart air sensor ($329). Its app is simple and informative, measuring nine different factors like humidity, CO2, and the virus index (the chance of virus survival). Unfortunately, it's too pricey to recommend to everyone, but if you really feel like something is amiss in your house, the cost may be worth it.

Start With an Air Purifier

We've already established that all our air is dirty, so the one thing all homes could benefit from is an air purifier. Every expert I spoke to agrees. “A good air purifier can only help,” Siegel says. “It will never make things worse.”

Quality purifiers eliminate things like dust, pet dander, and pollen from the air, which should alleviate coughing and sneezing. They can also be extremely helpful during wildfires, and if you live in a particularly polluted city.

“In general, these air purifiers have a small fan and some type of filter,” says Joe Heaney. “They continually bring air across that filter, removing, catching, or destroying pollutants and pathogens that might be in it, and dispersing the clean air back into the space.”

Adding a purifier to my apartment helped cut my cat-allergy-induced sniffles and stuffiness, but no air purifier can do all the work alone. You'll still need to regularly vacuum and disinfect, as well as keep the actual purifier clean and replace the filters as necessary.

“Unfortunately there is no silver bullet solution regarding indoor air quality," Heaney says. "Air purifiers do not eliminate the cause of pollution, nor are they able to capture it all at once. They simply clean it little by little. They can mitigate risk, but as outdoor air and people enter a space, the risk of pathogens and pollution will still exist in your home.” 

While high price doesn't equal quality, good air purifiers are not cheap. We have a full air purifier guide with several different options and price points after several years of testing models in different cities and home sizes.

Coway makes our favorite for small and large rooms. The Airmega 200M ($230) is our favorite for spaces up to 361 square feet. It's compact and nice-looking, plus it will kick on when its air-quality monitor detects higher pollution. The Airmega 400 ($500) is our favorite for rooms up to 1,560 square feet, where it cycles the air twice per hour. It's intuitive to use, with touch controls and a nice color-coded air quality light ring. 

If you have multiple issues to address and can spend $800, we love Dyson's Pure Humidify + Cool (9/10, WIRED Recommends). As the name suggests, it purifies, humidifies, and cools the air (but read about humidifiers below first).

Do You Need a Dehumidifier?

According to the EPA, indoor humidity levels should be around 30 to 60 percent—this is where an air quality tester will help. When it gets higher than that, it can feel muggy and damp. Too much humidity inside can cause problems like mold and worsening allergies. Paint can peel and crack in high humidity too. Siegel says it's much better to fix the moisture problem at its source, like targeting pipe leaks or basements with condensation issues. However we don't all have the freedom to know what's happening inside our walls, especially if we're renting, and such problems are expensive to fix. In that case, a dehumidifier can help if used correctly and cleaned diligently. 

“Dehumidifiers are fine in general,” Siegel says. “The challenge is that they’re energy-intensive and they don't fix the root of the problem. They’re a stopgap. They have their role, but people shouldn't use a dehumidifier and think ‘problem solved.’"

You probably don't need to run a dehumidifier all year, and you want to be careful not to remove too much moisture in drier months. Depending on where you live, summer is typically when you'll need to break it out. WIRED senior writer Scott Gilbertson recommends the Midea 35-Pint Smart Dehumidifier ($249). It has a clever, compact design that fits the actual dehumidifier into the water storage tank, so it takes up less space when you aren't using it. Plus, it can be controlled using its accompanying smartphone app—useful for when you're running it in a basement or garage. The pint number refers to the amount of moisture it can remove from the air per day. There are also 20-pint and 50-pint versions.

It's important to empty humidifiers frequently and to keep them clean. A dirty humidifier will cause more harm than good. Dehumidifiers draw out moisture and if left to sit, as Siegel explains, they accumulate a biofilm that can release mold spores and potentially harmful microbial VOCs.

Read the included booklet for the best instructions, but generally you should give it a good rinse every time you dump the tank, which you should probably do every day. Thoroughly clean the entire machine once a month with a white vinegar solution. Keep tabs on the filter too, and replace it as necessary.

Are Humidifiers a Good Option?

It sounds a little crazy to want to add humidity to your home—when I think of humidity, I think of frizzy hair and a permanent sweat mustache—but indoor air can get too dry, especially during the winter months. When humidity levels drop in your house, your skin and hair can dry out. Your nose dries out as well, causing stuffiness and potentially even snoring. Last winter, WIRED wrote about how dry environments make it easier for Covid-19 to spread, and this has been proven true with standard influenza too. Your wood furniture can suffer from drying and cracking too, as can your houseplants.

Humidifiers pump moisture into the air, hopefully getting it back to that healthy 30 to 60 percent window. I like to use one when I'm sick, and I have started using the Hey Dewy Portable Humidifier ($39) on my bedside table or desk when my skin is starting to look particularly flakey.

The devices are not without potential risk though. “Humidifiers are more complicated,” Siegel says. “In fact, I almost never recommend them unless you can maintain them.” They can emit a lot of particles into the air—“On the danger of the particles, we don’t really know, but we know enough to be concerned about it.”

In order for a humidifier to get moisture into your air, you have to fill the tank with water. But water isn't perfect. If you live somewhere with hard water, you may notice a white dusting on the furniture around your humidifier. Using distilled water is better, Siegel says, but still not a perfect solution. “In our experiments, we saw a reduction of about a factor of five between Toronto tap water and ultrapure laboratory distilled water,” he says. “But even distilled water becomes undistilled when it is exposed to air. It is definitely better than nothing, but only a partial solution.”

Even with a perfect water scenario, you have to be dedicated to keeping the device clean. Like dehumidifiers, they can do more harm than good if left unchecked. “Humidifier lung,” which is caused by breathing in air that's been contaminated by microorganisms, can feel like an asthma attack, where it's hard to catch your breath. To keep this from happening, you should rinse and dry the tank every day and scrub it completely once a week, using the same white vinegar and water solution you'd use for a dehumidifier. 

If you're sure you really need a humidifier, and are dedicated to cleaning it and changing the filters frequently, it could help during dry months. We have yet to try a ton of models, but the Dyson Pure Himidify + Cool ($800) mentioned above is a great multifunctional device that even self-cleans and alerts you when it's time to deep clean. That's great for keeping you from forgetting about it, but it's a huge investment.

We wish keeping our air quality safe and clean was as easy as buying a few products, plugging them in, and forgetting them, but it isn't. All of these devices are pricey, and they require proper use and upkeep to work effectively. However, what we've listed here are things you can still do to stay ahead of indoor pollution, and breathe a little easier.

1Update, August 2 at 11:45 am: This story was updated to correct an error. The maximum size of fine inhalable particles is 2.5 micrometers.

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