“Blow, Blow Thou Winter Wind”: Indoor Air Quality in Winter

Woman sitting on bad in front of window with snow covering forest landscape

Ah, winter. It doesn’t matter how fierce it gusts outside, we’ll be cocooning cozily by the wood fire in our well-insulated homes. As William Shakespeare once wrote:

“Blow, blow, thou winter wind,

Thou art not so unkind

As volatile organic compounds”

Or that’s what Shakespeare would have written if he had known just how poor air quality can get when we are trying to keep warm. 

Indoor air quality (IAQ) is vitally important because—this may come as a shock—people spend a lot of their time breathing. On top of that, most of these breaths happen indoors. Thus, whatever lurks indoors enters the lungs and sometimes the bloodstream. Symptoms of bad air quality can include anything from itchy eyes to death, with everything in between. 

What causes indoor air pollution?

We will detail the many different varieties of indoor contaminants in an upcoming article. For now, though, here is a brief overview:

Viruses & Bacteria: Let’s assume you are already very familiar with the work of viruses & bacteria. Let’s also assume that when they infect your respiratory tract, you’re not a huge fan.

Particulate Matter: This is a catch-all phrase for a mix of solid and liquid particles suspended in the air, often small enough to be inhaled. Particulate matter comes from hundreds of different sources including dust, ashes, smoke, pollen, construction, and combustion. PM2.5 (that is, particles smaller than 2.5 microns) are considered particularly dangerous. They exacerbate asthma and heart disease, and can decrease lung function. Another type of particulate matter, PM10, is larger but still small enough to be inhaled. It also poses a health risk, albeit likely a lesser one than PM2.5

Allergens: Allergens such as dust, pollen, and pet dander often occur in the form of particulate matter (though their sizes vary greatly). Even when they aren’t small enough to cause long term health problems, no one wants a runny nose from inhaling Muffin’s skin flakes.

Mold: If things get too humid, you may see this guy starting to grow in the dark corners of the bathroom. Mold sends out spores which can exacerbate respiratory conditions. Some species even release volatile organic compounds.

Carbon Dioxide: Human beings expel this gas from their lungs constantly. Poor ventilation can lead to unhealthy levels of carbon dioxide indoors. In high enough concentrations, carbon dioxide can impair cognition and increase anxiety.

Carbon Monoxide & Other Combustion Gasses: When you burn fuel (whether that fuel is wood, gas, oil, or kerosene) many gases are produced as a byproduct. Carbon Monoxide, being as efficient of a killer as it is, gets all the press. However, other gasses such as nitrogen dioxide and nitric oxide may be produced as well; all are unhealthy at high levels. Nitrogen dioxide might even be a cause of asthma in children.

Volatile Organic Compounds (VOCs): As defined by the EPA, “Volatile organic compounds are compounds that have a high vapor pressure and low water solubility.” Confused yet? Basically, VOCs are carbon-based gasses that generally smell funny and aren’t particularly healthy to inhale. They tend to bleed into the air (“offgas”) from paints, carpets, pesticides, furniture, craft materials, and pretty much anything that was made in a factory.

Radon & Asbestos: These two contaminants usually only occur where something has gone wrong, but “wrong” in this case could mean simply poor ventilation or ongoing renovation.

Radon is an odorless, radioactive gas that results from the breakdown of uranium in the soil. The concentration is usually too low to worry about, but in areas of a house with poor ventilation, natural radon can build to unsafe levels. The EPA recommends that every American have their house tested for unsafe levels of radon, as it is the second leading cause of lung cancer.

Asbestos is a common but extremely dangerous building material found in everything from insulation to painting to flooring. Most uses are carefully controlled to ensure it cannot normally enter into the air. However, once asbestos gets in the lungs (say during renovation, construction, or damage), it never leaves. Asbestos fibers damage the lungs more and more over time until serious and often deadly health complications develop. 

Radon and asbestos both require special handling and mitigation by experts. The suggestions in this article do not necessarily apply to radon and asbestos mitigation. If you have concerns about radon or asbestos, please consult a trained professional.

How to measure air quality

Unfortunately there is no one indoor air quality test for all these contaminants, although certain home air quality monitors can cover many at once. For something as deadly as carbon monoxide, you’ll want to install a detector in your home 24/7. For others like radon, you’ll need to call a professional. We’ll explore the many facets of air quality testing in an upcoming article. ActivePure’s partner Aerus also offers a free home air testing service to customers; contact your local dealer to learn more.

Why is indoor air quality particularly important in winter?

“Out of the bosom of the Air,

Out of the cloud-folds of her garments shaken,

Over the woodlands brown and bare,

Over the harvest-fields forsaken,

Silent, and soft, and slow

Descends the snow.”

— Henry Wadsworth Longfellow, “Snow-flakes”

Air quality is worse in winter

Cold air can stagnate, forcing warm air to flow over it. This means a cap of cold can form outdoors, trapping in smog and pollution closer to the ground. Basins with large cities are particularly susceptible to this effect. If air quality gets worse outdoors in winter, is indoor air quality better

Unfortunately, no. Because of reduced ventilation, indoor air quality often has concentrations of contaminants which would be illegal outdoors; some contaminants exist indoors at two to five times the level of outdoor air! This phenomenon is not exclusive to the winter, but we shall see, winter does not improve it.

People spend more time indoors.

We spend 90% of our lives indoors, according to the EPA. If you live in a colder climate, you will be breathing indoor pollutants in the winter even more than you did in the summer (which was already quite a lot).

More Indoor Gatherings

Regardless of what winter holidays you celebrate, you will almost certainly be celebrating them indoors (Polar Bear Plunge excepted). And that’s wonderful. We’re not saying you shouldn’t invite Great Aunt Maybel to Thanksgiving. Just be aware that she is adding one more source of humidity and carbon dioxide to your indoor climate. When Uncle Omar decides to repay your hospitality by re-calking the tub, he’s putting plenty of VOCs into the air. And when Grandma starts frying up Latkes, she’s adding some extra particulate matter and nitrogen dioxide. Don’t forget about cousin Renaldo’s covert smoking habit or the fact that little Chioma has an asymptomatic flu.

Cold and Flu Season

Speaking of the flu, the increased spread of respiratory illnesses during the winter is another reason to be aware of indoor air quality. Human beings shed a lot of viruses into the air. For instance, one sampling of 1400 tourists in NYC found that one out of fourteen were shedding respiratory viruses. If people out-and-about on their summer vacation (and thus presumably feeling okay) shed this many viruses, it is a safe assumption that the situation is even worse in the colder months.

Infection rates are higher during the colder months because of lower moisture in the air (at least, this is one theory). When a sick person exhales, they expel droplets containing viruses into their environment. In the winter, these droplets dry out before they can drop to the ground, allowing the viruses to travel further. 

Heating System Hassles

Your heating system can reduce your internal air quality. Wood fires are cozy, but they increase the particulate matter both indoors and outdoors. As a reminder, PM2.5 irritates the lungs and can cause bronchitis. Over time, particulate matter can worsen asthma, lung cancer, and heart disease. Even if your fireplace is properly vented, residential heating’s contribution to the country’s outdoor air quality still kills 10,000 Americans per year, and one study suggests most of this pollution comes from wood fires.

Almost any form of combustion can release unsafe levels of carbon monoxide into a home. 50,000 Americans head to the ER each year due to carbon monoxide poisoning, though most cases result from improperly installed, improperly maintained, or improperly operated heat sources. To avoid this fate yourself, make sure your heating system is properly inspected, maintained, and installed. Also, buy a CO detector.

Most Homes are Built to be Airtight

With all these dangers from winter heating systems, a seemingly obvious solution would be to make buildings more energy efficient. After all, more energy efficiency means less fuel used means better air quality, right? Well, not quite. 

Air exchange (the process by which a building vents indoor air and brings in outdoor air) occurs intentionally through vents, fans, and HVAC systems, and unintentionally through cracks in windows, doors, and joints; this latter method is called infiltration. Making a building more energy efficient usually involves reducing infiltration. However, if this infiltration is not replaced with additional intentional air exchange, anything which gets into the building’s air has a good chance of staying there, from cigar smoke to sneezes. Thus, hazardous air quality could be the unintentional result of energy efficiency.

How to Improve Indoor Air Quality in Winter

“Winter under cultivation

Is as arable as Spring.”

—Emily Dickinson, “Winter under cultivation (1707)”

According to the EPA, there are three strategies for improving internal air quality in winter: source control, improved ventilation, and air cleaners.

Source Control

The simplest way to improve internal air quality is to reduce contaminants at their source. Source control is obvious, if not always easy, for a clear and present danger like cigarette smoke. Other sources take less self control, but more investment. Repairs to chimneys, wood stoves, oil burners, and other heat sources might be expensive, but breathing in the particulate matter exuded by improperly maintained heat sources will be far more costly to your health.

Switching from a gas to an electric stove can reduce indoor pollutants in your home. Gas stoves release Nitrogen Dioxide as a byproduct, which can irritate chronic lung ailments, and perhaps even cause them in children. The World Health Organization recommends keeping indoor Nitrogen Dioxide level at five parts per billion (ppb), but cooking with a gas stove can spike these levels to 168 ppb (or more) if you have a poorly ventilated kitchen. Gas stoves also release other harmful compounds and particulates at a higher rate than electric stoves. If you cannot afford to swap out your gas stove for an electric, make sure you have as much ventilation as possible when cooking.

Another fix is to change how foods are cooked and what foods are cooked. A University of California compilation of various cooking studies found that meat and foods with low water retention released more emissions than vegetables and foods with high water retention. This same paper found that emissions were 2.5 times higher when cooking on high heat, rather than on medium heat (though the definition of “high” and “medium” here may not be the same as those on your stove dial). 

You may have heard about emissions and oil smoke points. Oils with a low smoke point start releasing emissions at lower temperatures. However, before you change your favorite cooking oil, keep in mind that there are multiple variables when looking at emissions from cooking oils (not to mention a host of contradictory advice on which oils are best). Some oils with a very low smoke point  also have low emissions because they have a high oxidative stability. Rather than changing your oil, try heating the oil more slowly instead. And, as always when cooking, ventilate. Speaking of ventilation...

Improve Ventilation

Source control is of limited use when you can’t remove the source. And sometimes you just have to paint your walls (or your nails). That’s why there’s ventilation.

The simplest way to ventilate is to open the windows. If you live in a warmer climate (or an old building with an overly-aggressive radiator), this won’t be a problem. However, this isn’t practical year-round for most.

https://pixabay.com/photos/winter-sky-snow-outside-chimney-3285527/Fortunately, homes already have certain built-in methods of ventilation:  bathroom vents, attic fans, and kitchen range hoods. The first two of these are almost always designed to blow contaminated air outdoors, which draws in new outdoor air automatically. Kitchen range hoods are either ducted or unducted. Ducted hoods vent air outside, while non-ducted hoods recirculate the air through a filter. Whenever you are cooking, painting, sanding, welding, smoking, installing new carpets, or performing any other activity which releases contaminants into the air, please turn on one or more of these ventilation options. Or per the EPA, “You might also choose to do some of these activities outdoors, if you can and if weather permits.”

Another method of ventilation is to install a heat recovery system in your existing HVAC system. These may be referred to as MHRVs, HRVs, or ERVs, but they all work on the same basic principle. Fresh air is drawn from outside the house into a chamber containing a heat exchange (and sometimes also a moisture exchange). At the same time, stale air from inside the house is drawn into the same chamber. The air streams are kept separate, but the heat exchange is able to distribute energy, preserving much of the indoor heat. Air from inside the house is then vented outdoors, while the outdoor air (now the correct temperature) is pumped in. This is an energy efficient way to draw fresh air constantly into the house, but it does require an initial investment

Air Cleaners

You may require a supplement to ventilation and source control. This is where air cleaners come in. Air cleaners can take the form of portable units, or they may be built into an existing HVAC system.

Two common types of air cleaners are HEPA filters and activated carbon filters. HEPA filters draw air through densely woven fibers, and are excellent at removing particulate matter and allergens. Activated carbon filters draw air through carbon tubes, absorbing odors and certain harmful gasses. 

When selecting a HEPA-based or carbon-based cleaner for your home, consider your room size. Most cleaners should tell you how large of a room they clean. This is based on a filter's CADR (Clear Air Delivery Rate), which determines how quickly it removes particles. Also, the EPA recommends using a filter with a MERV (Minimum Efficiency Reporting Value) rating of at least 13. MERV measures how efficient the filter is at removing the most harmful particulates.

Air Purifiers

The problem with air cleaners is twofold: First, they only remove certain types of contaminants. HEPA is great for particulate matter but not so great for gases, viruses, or mold. Carbon filters are effective at removing odors and certain gases but nothing else. 

The second problem with cleaners is that they are passive. That is, they wait for the contaminants to be drawn through their mechanism. 

The solution to this problem is active air purification. Active purifiers create scrubbing molecules from water vapor, distributing them throughout a space. These molecules actively take apart viruses, bacteria, mold spores, and volatile organic compounds. In fact, ActivePure’s own technology has been proven to reduce 99.9% of many pathogens in minutes, not just in the air but on surfaces. An ActivePure purifier plus a HEPA cleaner to remove particulates (some of our units have both) is an incredibly powerful combination for improving internal air quality in winter.

A Few Final Words

“Mistletoe hung from the gas brackets in all the front parlors; there was sherry and walnuts and bottled beer and crackers by the dessertspoons; and cats in their fur-abouts watched the fires; and the high-heaped fire spat, all ready for the chestnuts and the mulling pokers.”

—Dylan Thomas “A Child’s Christmas in Wales”

With as much time as human beings spend indoors, we ought to be doing all we can to ensure that those indoors are healthy. However, indoor air can become riddled with contaminants from cooking, heating, renovating, or just breathing. Proper source control, ventilation, and air purification can go a long way towards making our homes as healthy as they are cozy.

Scroll to Top