Winter Indoor Air Quality: Preparing for the Cold Months Ahead

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November 18, 2020

We know. It's difficult to believe the winter solstice and the holiday season are already here.  Unfortunately, the cold season is one of the worst times of year for indoor air quality, either at home or at work. People huddle inside tightly-sealed buildings and trade ventilation for heating. This traps pollutants and moisture in, which is a recipe for bad air.

And that’s in normal times. COVID-19 numbers are staying stubbornly high, and second waves are occurring. People spend 90% of their time indoors as standard. This winter, people will be cooped up indoors even more than usual – and the risk of spreading the coronavirus is raised in enclosed environments

All the more reason to be as prepared as possible.

What Makes Winter Indoor Air Quality Worse?

Safeguarding Against COVID-19 During Winter

With the winter season looming and COVID-19 still a threat, it's crucial for people to know how to optimize their indoor air in a way that minimizes the risk of infection.

In an  "Ask An Expert" column in Colorado University Boulder Today, Shelly Miller, a professor of mechanical engineering and expert in indoor air quality, urges people to adhere to state and county and city guidelines and public health orders. Households that plan to have gatherings during the winter season are encouraged to limit the frequency and the size of their gatherings. Social distancing and wearing of masks must be strictly observed when homeowners plan to have people over.

"If you’re having people over at your own home and talking, you’re going to be generating a ton of aerosol," Miller points out. "The only way to keep yourself safe in that space is to wear a mask. You have to wear a mask if you want to hang out and talk with other people and share their air."

Miller also advises to periodically open the window for 10 to 15 minutes to keep indoor air clean. "Yes, it will get cold, but you've now brought fresh air in and you've exhausted warm air," she adds.

You may also want to consider implementing added measures to keep indoor air clean. These measures could include adding air purifiers or upgrading air filters to a higher MERV rating. Incorporating these into a building's existing HVAC system increases the quality of air by removing particles, germs, viruses, and chemical gasses.

Why Tracking Indoor Air Quality Matters

Knowledge is power. Until you know what issues you are having with your air, you can’t correct them. The most common driver of winter indoor air quality issues is too much moisture. However, before you can be sure that this is your issue, and decide how to improve indoor air quality in winter, you need the data. You need to be aware of what is affecting your IAQ. This is where tracking comes in.

Having a smart device that tracks the main factors of poor indoor air quality is a crucial first step. An effective IAQ monitoring system should at least (1) indicate if the level of moisture or other metrics reach unacceptable levels, (2) share insights as to which part of the house is contributing to this rise, and (3) offer recommendations to fix the issue.

A good IAQ monitoring system can track the factors that contribute to poor indoor air quality: Not only humidity, but temperature, levels of dust, VOCs, and CO2.

How to Improve Indoor Air Quality in Winter

Once you start tracking your winter IAQ, you will know what your problems are. From here, you can start implementing solutions.

Before you know exactly what these solutions should be, you need to know your unique situation. However, the road to remediating your winter indoor air quality may well be easy and inexpensive. Some frequent actions that help include:

It may seem surprising that winter is almost here in full. However, the cold season is the worst season for indoor air, and it’s never too early to start getting prepared.


  • Sealing in the pollution – When it’s cold, everyone shuts up all their windows and doors. However, this traps in VOCs, dust, and other harmful airborne molecules. The EPA is very clear that inadequate ventilation in homes and buildings increases air pollution levels.
  • Smoke from fireplaces – Wood fireplaces are often the go-to choice for warming up homes without increasing the heating bill. However, when the air gets cold and dense during the winter, smoke experiences more air resistance. This causes more of it to be trapped within your home, which can cause health problems. Wood smoke, if left unchecked, raises exposure of residents to hazardous amounts of PM2.5, which can cause a range of ill effects.
  • Over-humidifying – Cold outdoor air is “dry”, so people often compensate by turning on their humidifiers. However, not tracking the right level of humidity in your home can lead to mold growth and dust mites. Mold can cause serious problems for both buildings and people’s health.
  • Prolonged presence indoors – Human beings give off a lot of water vapor every day. Tiny water droplets floating in the air are trapped inside your house. As water vapor level increases, air temperature gets warmer. This translates to a spike in humidity. And when humidity rises in an indoor setting, the environment becomes less hygienic and more conducive to bacteria, mold, and viruses.