Health Experts Explain Why You Should Avoid Window AC Units When Air Quality Is Bad

• Due to wildfires in Canada, millions of Americans across the Northeast, Southeast and parts of the Midwest are experiencing extremely poor air quality.

• Staying indoors and turning on your air conditioning can minimize some of the health risks associated with outdoor smoke pollution, but experts agree the benefits depend on which type of AC unit you own.

• Specifically, recirculating indoor air when possible — as opposed to using fresh air intake from your home's exterior — is better advised.
  

With a majority of the Eastern seaboard of the United States dealing with extremely poor air quality, it's understandable if you're having trouble breathing — in fact, you're far from alone.

Per CNN, more than 75 million people across the Northeast, Southeast and portions of the Midwest have faced widespread outdoor smoke pollution this week stemming from wildfires in Canada, resulting in air quality alerts from multiple weather authorities. Smoke from wildfires is known to contain toxins and other byproducts that can make most anyone feel sick, but especially those with pre-existing respiratory conditions and other health issues.

But simply heading inside may not provide immediate relief, either; and if you don't have access to an effective air purifier, you may be wondering if turning on your air conditioner might help protect against the harmful airborne pollutants currently affecting countless communities.

The truth is that air conditioning may be an effective way to minimize some of the risks presented by deteriorating air quality inside your home — but it all hinges on which kind of air conditioning system you use, as AC isn't enough on its own to eliminate all risks to your health.

Primarily, air conditioning systems can prove useful in keeping you comfortable while your home's windows and doors are firmly sealed off from pollution outside. Our home engineering professionals in the Good Housekeeping Institute have long established that almost any well-made air conditioning unit improves indoor air quality by ensuring that humidity doesn't go unchecked. But for homes equipped with central air conditioning or split air conditioning systems (wall units that don't require window access), AC may provide an extra edge when it comes to air purification efforts in your home — whereas the opposite can be said for in-window AC units that may potentially pull in polluted air.

Can I use air conditioning when air quality is bad?

It's true that almost all mechanical air conditioning units are made with filtration systems, but some are inherently much more effective than others, explains Dan DiClerico, the director of the Home Improvement and Outdoor Lab at the Good Housekeeping Institute.

Ensuring your air conditioner's filter is up to date is crucial when you use AC during any poor air quality events in your area. If you have central air conditioning units, running your AC system when there's wildfire smoke or other widespread air pollution outside won't put you at greater risk for breathing issues — in fact, if your filter is up to date or has been replaced with a HEPA filter that has a greater Minimum Efficiency Reporting Values (MERV) rating, central air conditioning can be one tool, among others, to improve air purification.

"Central air conditioning systems treat virtually all the air in the house as it circulates through the system," DiClerico says. "A four-inch pleated filter has more surface area than one-inch cardboard filters, so they're going to remove many more particulates from the air."

Ronald Grifka, M.D., chief medical officer and clinical cardiologist with the University of Michigan Health-West, says that an effective air conditioning filter may effectively process more air in your home in a shorter amount of time compared to room air purifiers — upwards of 100 cubic feet per minute, though both solutions should be used for best results, Dr. Grifka adds.

"So you can really just clean and purify more air with an air conditioning system than a single, small, corner air purifier; from that perspective, air conditioning may be helpful," he says. "The average house built with proper air conditioning systems keeps too much air from the outside getting in; and any air that does creep in, a good filter can be quite helpful to keep the air inside the house as clean and safe as possible."

In short, air conditioners that are centralized (as well as split units that are anchored on walls) work to circulate air indoors without pulling in polluted air from the outdoors. Circulating this air removes heat and humidity, but it also puts air through filters that may capture potentially harmful particulates floating around inside, all on a repeated process that improves indoor air quality in the end.

Changing your air conditioner's filter as often as possible, and keeping them up to date, will ensure they are working at peak performance.

"The typical window unit, on the other hand, doesn't have much of a filter," Dr. Grifka adds. "If they do, they're plastic washable filters that catch flies and mosquitos, or larger airborne matter. But as far as particulate matter, it doesn't do much at all, unfortunately."

Is it a good idea to use AC when the air is smoky outside?

Again, it all depends on which kind of air conditioning you have in your home.

Those with centralized air conditioning and split units, which are designed to recirculate indoor air, may be able to marginally boost the efforts of air purifiers inside their home by running air conditioning simultaneously. Meanwhile, window units don't always provide the same benefits, as these air conditioners can pull air directly from outside into your home.

Vinny Lobdell, an industrial air quality expert with 20+ years of experience and former president of HealthWay and Pure Wellness, adds that window units make use of filters that are far less efficient in processing wildfire smoke, which contain small airborne toxins that are easily ingested in the lungs.

"Window units actually take the outdoor air inside, bringing it through the AC system and its condensing coil, pushing it through 'butterfly-catcher' filters that aren't really capturing small particles," he says. "If you choose to bring air in through one of those window air conditioning systems, you should definitely have an in-room air purifier to ensure you're cleaning the air very well."

Because window units may directly pull air from outside your home, they could introduce wildfire smoke into your spaces with very little filtering capability compared to centralized AC systems. DiClerico explains that some window units are equipped with an outdoor damper, which may be closed to reduce the amount of exterior air that is pulled into your home. In this case, these units should additionally be set to recirculation mode to ensure exterior air isn't seeping inside.

Ultimately, choosing to not use a window unit (or portable AC units that make use of window hoses) and ensuring its seal is as tight as possible is a cautious approach to ensuring exterior smoke doesn't end up inside your home.

Both Dr. Grifka and Lobdell agree: Those with preexisting respiratory issues and other health concerns, as well as those with young children living in the home, should not use window AC units that do not have air recirculation features when wildfire smoke is a concern.

"If you live with elderly people, people with emphysema or COPD, those with asthma, anyone with heart failure, young children; these people are most at-risk for developing symptoms stemming from exposure to smoke and poor air," Dr. Grifka adds. "Those are the people that need to be more careful… and may even consider wearing a mask until the air quality issue is resolved."

How to know when smoky, polluted air is a risk to your health

Unfortunately, there is no easy or affordable way to gauge or test the air quality inside your home. If you're worried about whether or not it may be safe to use air conditioning, the simplest, most straightforward way to determine risk is to consider your area's air quality index and monitor your own health symptoms.

Per materials published by the Centers for Disease Control and Prevention, breathing in wildfire smoke can worsen lung conditions, but may trigger breathing issues for most anyone. If you are coughing, have stinging eyes or an irritated throat, a runny nose, irritated sinuses, wheezing and shortness of breath, chest pain or are experiencing asthma symptoms, it may be a sign that your indoor air quality is compromised by wildfire smoke or other airborne pollutants. Working to reduce the airflow of outside air into your space (including limiting the use of window AC units) may be necessary at this point.

Normally, the published air quality index for your area will be a good indicator of how careful you should be in exposing yourself to polluted air. Anything above an index of 101 (officially known as "unhealthy for sensitive groups") may prompt you to exercise caution — and should indicate whether or not you should begin to use air purifiers, close doors and windows as well as other measures to keep exterior air out.

"You'll be able to compare every new day to previous days, see how this week compares to the next; the air quality index can help you determine whether you need to keep the air outside of your house," Dr. Grifka explains.

How to keep indoor air safe while air quality is poor

It's important to note that air conditioning alone — even those centralized systems that do not rely on processing external air only — is not the best tool for purifying the air inside your home. It's most effective when used in conjunction with other known, proven tactics that can help maintain good indoor air quality when there's a poor air quality index in effect for your area.

Here are some ways to improve indoor air quality alongside air conditioning, according to our Good Housekeeping Institute experts and leading organizations like the American Lung Association:

• Close all windows and doors. Place damp towels around window frames that are not snug in order to reduce the likelihood of polluted air leaking inside.

• Consider replacing AC filters that may be impacted by excessive wildfire smoke or other local air pollution events

• For those with a central HVAC that uses fresh air intake, close it and be sure set your system to recirculate indoors.

• Use a portable air purifier or high-efficiency filter to target fine particles.

• Avoid activities like smoking, burning candles and using a gas stove.

• Pause on vacuuming, as Dr. Grifka says it can stir up dust that is already inside your home.

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