How Long Should You Leave Your Window Open?

How Long Should You Leave Your Window Open?

There are few things better than the feeling of throwing open some windows after a long, stuffy winter. Fresh air has a way of rejuvenating people.

When the weather is nice, you may even want to have windows open every day for ventilation. 

How long should you leave your window open? You should leave your window open for about 15 minutes a day to thoroughly ventilate your home. The time will vary somewhat according to how well-sealed your home is, and local air pollution may cause you to aim for a shorter amount of time.

We will discuss these factors in detail so that you can make an informed decision on how long you should keep your window open.

A Brief Explanation of Indoor Ventilation

Ventilation is merely the process of replacing indoor air with outdoor air. It’s like your home is breathing. It exhales the stale indoor air and inhales the fresh outdoor air.

Just like a human needs to breathe, so do buildings and homes. Unfortunately, modern home design favors air-tight houses, making ventilation a challenge.

We don’t help the matter by spending the majority of our lives inside with the windows locked up.

There are different ways your home can “breathe,” and there are three basic types of home ventilation (source):

  1. Natural ventilation 
  2. Spot ventilation 
  3. Whole-house ventilation

The U.S. Department of Energy describes natural ventilation as an “uncontrolled air movement” from doors, windows, and even cracks in a home. 

Spot ventilation involves the use of specialized exhaust fans to ventilate the air in one area or room. The best example of this is a range hood over an oven.

Whole-house ventilation requires a fan-and-duct system to exchange the air inside a house. It is a uniform and controlled air movement.

When you open the windows in your home, you are utilizing natural ventilation. As with most “natural” things, this is usually the safest and quickest option. 

Both spot ventilation and whole-house ventilation require specialized equipment, and some of this equipment can be pricey. 

On the other hand, natural ventilation requires nothing except the ability to open a window. There isn’t any special equipment, and there isn’t a need to call a contractor.

Still, you might not be convinced. After all, you aren’t paying to heat the outdoors. 

While this concern is valid, what could be worse than a higher electric bill? The answer: air pollution.

If you’re thinking to yourself, “My home isn’t polluted,” read on because it actually is.

Should You Air Out Your Home?

Without a doubt, yes. According to the EPA, humans spend nearly 90% of their time indoors (source). With this statistic in mind, we should aim to keep the air in our homes clean.

Still, just how unclean can air inside a home be? Short of living next to a smokestack, you’d have to work to pollute the air inside, right?

As it turns out, indoor air is subpar and is 2 to 5 times more polluted than outdoor air (source). Indoor pollution comes from numerous sources, which makes it hard to combat. 

Tobacco use is an obvious source of indoor pollution, and smoking three cigarettes inside is worse for the air than having a running diesel engine in your living room (source). 

Moreover, the way a home is heated can result in low air quality. Coal or wood burners and fireplaces create smoke and soot which pollute the air. 

This smoke carries over 100 chemical compounds through the air of such homes.

Public health organizations consider most of these chemicals to be carcinogenic. Even if these chemicals don’t cause cancer, they can cause several dangerous respiratory illnesses (source). 

Another polluting offender is kitchen appliances, and ovens, in particular, are guilty. Air contamination is the main reason why cookers require ventilation air vents (source).

Depending on the type and install of the vent, it could suction up 100% of the contaminated air. Unfortunately, plenty of ovens can only remove 10% of these air pollutants (source). 

Benefits to Airing Out Your Home

It’s good to open the windows to let in fresh air and sunlight for your health. Vitamin D from the sun helps boost your immune system while circulating air removes pollutants that can make you sick.

Sick Building Syndrome, or SBS, is a well-documented phenomenon where occupants of a building all fall ill with the same symptoms with no apparent cause (source). 

SBS is more common in workplaces, especially older buildings, but residences are not immune to the problem. 

How can you know if an illness is related to being indoors? Simple. Step outside for a while and see if your symptoms improve. If you spend the night somewhere other than home, do your symptoms disappear? 

Air Changes Per Hour

SBS has a laundry list of causes, but the main one is related to ventilation issues. It’s a relatively new problem since before the 1970s, buildings and homes weren’t very energy-efficient. 

The 1970s saw an energy crisis, and a decade-long oil embargo led to skyrocketing gasoline prices. As a result, the economy took a nosedive (source).

After the crisis passed, government agencies and professional associations strengthened building guidelines to the point where buildings and homes became practically air-tight.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers, or ASHRAE, designs the current guidelines for residential ventilation. Per these standards, ventilation must be at a minimum of .35 air changes per hour (source).

If you’d like to calculate the air changes of your home, you will find that information under this article’s Air Exchange Rate section.

Following these new guidelines, home builders all over America made sure their structures were tightly sealed, and they filled in any leaks they discovered. They updated the windows and improved roofs.

These guidelines stopped natural air exchange in its tracks, and we became victims of our own success. 

Air-tight structures may be a good thing in some cases, but not when it comes to buildings human beings occupy. While energy efficiency increased, our air quality decreased. 

Without natural air exchange, we now need to monitor our health for things like SBS. We have to regularly open windows to ventilate.

SBS isn’t the only health concern. The World Health Organization, or WHO, recognizes the dangers of poor ventilation.

Poor air quality and ventilation can lead to the transmission and spread of respiratory diseases (source).

For example, healthcare facilities with low ventilation have higher rates of disease transmission for staff, patients, and visitors alike.

Signs that You Need to Air Out Your Home

The cue to air out your home comes from you. Take stock of your body and health. If the air quality in your house is low, you may have symptoms to show it.

The following symptoms and issues are associated with low indoor air quality:

  • Coughing
  • Sore throat 
  • Shortness of breath
  • Itchy eyes
  • Headaches
  • Asthma attacks

If you are experiencing several of the above symptoms with no reasonable explanation, it’s time to ventilate your home (source).

You might not have any of those symptoms, but that doesn’t mean your home’s air quality isn’t low. There are other signs that your home needs ventilated. 

Think back to the last meal you prepared with onions. Did its fragrance dissipate reasonably quickly, or did the odor linger?

Perhaps the smell traveled throughout your whole home, and suddenly you found yourself in a house seemingly made of onions.

A well-ventilated house can shuffle out odors, and a well-ventilated kitchen would keep any food odors from traveling to the rest of the house. 

Lingering odors are evidence of inadequate air exchange. Simply put, the old air indoors isn’t being exchanged with fresh air. 

Likewise, you need to check your home for excessive moisture. An obvious symptom of this is condensation or “weeping windows.” This is when condensation builds up on a window.

Everyday activities like showering and cooking add moisture to the air. Normal levels of humidity usually isn’t an issue for older homes since home builders used to design homes to withstand this.

The modern air-tight home, however, doesn’t let this air escape, preventing fresh, dry air from replacing it (source). All the moisture you create from your everyday routines is trapped and hanging heavy in the air.

If you see weeping windows, your house is probably lacking ventilation. It’s time to air out your home regularly. 

How To Air Out Your Home

If, by now, you’re concerned about the necessity of airing out your home, don’t worry. The remedies are fairly simple.

With most humans spending their lives indoors, we all could use some fresh air. For the best results, follow the procedures below.

When Should I Air Out My Home?

You should air out your house as much as possible; every day is ideal, and twice a day is even better no matter the season.

In fact, ventilation in the winter may even be even more important and should still be part of your daily routine.

Image by Toa Heftiba via Unsplash

This is especially true if you have a wood-burning or coal-burning stove. As I mentioned before, the smoke and soot from these stoves are full of harmful chemicals and pollutants.

If you are able, aim to air out your home once in the morning and once later in the day. You want to aim for times of lower outdoor pollution for the best results. 

The degree to which you have to factor in air pollution will depend heavily on your location.

For example, a large city is more likely to have heavy air pollution than in a rural area. On pollution lists, the large cities in California take the top spots (source).

If you’d like to know the air quality information for your area, you can visit AirNow. At the organization’s website, you can input your zip code and get a whole week’s forecast for the air quality in your area.

For most areas, your best bet is early in the morning or late at night, so you can avoid pollution from traffic.

Some outside factors can affect nighttime air quality, though. In winter, late evenings have been found to have more air pollution thanks to the use of fireplaces (source).

For the most consistent quality air, aim to open your windows between 5:00 AM and 10:00 AM. This is the timeframe when pollution is regularly the lowest in most areas.

If you are so inclined, you can even sleep with the bedroom windows open all night. Only leave them open a crack to avoid a scary electric bill. A study from the Netherlands did find an open window can improve sleep quality (source).

What is the Best Way to Air Out My Home?

You may think your home is well-ventilated. After all, you have ceiling fans and an oven exhaust vent, and your laundry’s exhaust goes straight outside. 

While these measures are helpful, they aren’t enough. Fans, for one, don’t ventilate. They simply circulate the existing and possibly polluted air that’s already there.

Likewise, there’s a strong probability that you aren’t using that oven vent.

The Ernest Orlando Lawrence Berkeley National Laboratory performed a study on kitchen ventilation, where the researchers surveyed people to find out if they use their oven’s ventilation system (source).

Only 13% of gas stove owners use their ventilation system frequently. 10% never use their ventilation hood, and 21% didn’t even have a vent.

Of those who never use the ventilation system, 48% believed it wasn’t necessary, and 21% didn’t use it due to the noise it created. 

Long story short, your house needs ventilation, no matter how many extra measures you are taking. It’s better to have clean air than to be sorry.

For maximum ventilation, you should open everything. Every window and every door should be open to the fresh air at least once a day.

If you are concerned about insects making their way indoors or letting in outdoor pollutants, you can utilize screen doors and screen windows.

You can even use trickle vents. Trickle vents are small openings in windows that allow air to exchange without actually opening the window. They allow fresh air to come in but don’t allow heat to escape (source). 

With trickle vents in most of the windows, you won’t need to open windows daily because these vents provide background ventilation 24/7.

Trickle vents are worth the price in the long run, but upfront costs may lead you to decide in favor of just opening your windows instead.

How Long Should I Air Out My Home?

Believe it or not, 15 minutes with the windows open should be enough time to exchange the air in your household. Fifteen minutes sounds like a short amount of time, but it’s just enough time to refresh your whole home.

Of course, you don’t have to limit yourself to 15 minutes; that’s just the minimum amount of time it takes.

Understanding the air exchange rate of your home will give you a more precise measure of the time it will take to air out your house. The air exchange rate measures the number of times a room’s air gets replaced in an hour.

Air Exchange Rate

The formula for the air exchange rate is n = 60 q / V  standard or  n = 3600 q / V metric.

In this equation:

n= air changes per hour.

q = fresh air flow through the room in cubic feet per minute or cubic meters per second.

V = the volume of the room in cubic feet for standard or cubic meters for metric.

For example, if you had a room that was 700,000 cubic feet with an airflow of 6000 cubic feet per minute, you would have about 0.51 air changes per hour.

60 (6000 f3/m)/(700,000 f3)=0.51

If you’d like to know an air exchange rate for a particular area without so much math, you can just use these averages (source):

  • Without windows or exterior doors – 0.33 changes per hour
  • With windows or exterior doors a single side – 0.67 changes per hour
  • With windows or exterior doors on two sides – 1 change per hour
  • With window or exterior doors on three sides – 1.33 changes per hour

These numbers are based on a very well-insulated and tightly sealed home. However, 15 minutes at 4 air changes per hour is usually enough time for a single cycle of air exchange for an average home. 

If you don’t mind keeping some windows and doors open longer, nothing is stopping you from getting a few more exchanges of fresh air in!

Is There Anything Else I Can Do?

Yes! Beyond just regularly ventilating your home, there are other things you can do to improve the air quality (source).

  • Invest in a heat recovery ventilator (HRV)
  • Get an air purifier
  • Have some plants around your house
  • Quit the cigarettes
  • Stop using spray air fresheners
  • Have oven gas jets serviced

A heat recovery ventilator (HRV) pulls in stale air and replaces it with fresh air. The one-time cost of an HRV is pricey, but it will help with your energy bills in the long run.

Air purifiers are handy appliances that pull in air and remove things like dust, pollen, and germs. Plants can help clean indoor air and remove toxins. Just take care of them, and they’ll take care of you.

If you are a smoker, this is just one of the hundreds of reasons to throw out the cigarettes.

The chemicals (VOCs, specifically) in spray air fresheners contribute to low indoor air quality, so freshen up your house with open windows instead.

Serviced gas jets on ovens burn gas more evenly and prevent adding chemicals to indoor air.

Final Thoughts

We may be able to live without a lot of things, but fresh air just isn’t one of them. If you don’t ventilate your home regularly, you could be endangering your health.

Fortunately, airing out your home isn’t hard to do. With every door and window open, your house can get a whole home refresh in as little as 15 minutes.

For the best times to throw open the windows, check the air quality forecast for your particular area. In general, mornings between 5:00 AM and 10:00 AM have the lowest levels of air pollution. 

After getting through this article, surely you’ve come to appreciate the need to ventilate your home. Still, it isn’t just about health. Some fresh air flowing through your place can be the most refreshing feeling!  


I'm a Pharmacist and a passionate researcher into clean air and pure water for the home. I believe these 2 elements play a significant role in our health and overall wellbeing.

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