This Simple Winter Habit Can Improve Your Indoor Air Quality in Just 5 Minutes

When winter is in full swing, many homeowners want to keep their homes sealed to avoid losing precious heat. But this seemingly simple desire to trap the warmth in can often do more harm than good. Leaving your home sealed during winter can lead to issues such as excess moisture, stale air, and trapped indoor allergens. Instead, briefly opening your windows (even for a few minutes each day) can make a big difference in your home's ventilation. Ahead, we consulted HVAC experts, who shared the reasons why opening a window daily during winter can be so beneficial.

Benefits of Opening Windows in Winter 

Cracking a window in winter is an easy task—and these reasons will convince you to make it a regular habit.

Decreased Carbon Dioxide Levels

Indoor carbon dioxide (CO2) levels naturally rise when a home is closed up for long periods, especially overnight or in households with multiple occupants. Elevated CO2 is linked to fatigue, headaches, and poor sleep quality, and can also make the air in your home feel or smell stale.

Cracking windows for even five minutes makes a real difference when it comes to controlling your home's CO2 levels, says Josh Mitchell, HVAC technician and owner of Air Conditioner Lab. "I've tested CO2 levels in homes after being shut for a few days. The readings increase from 600 ppm to more than 1,200 ppm. Opening two windows facing each other for five to 10 minutes quickly brings it back under 800 ppm."

Healthier Indoor Air Quality

Besides CO2, stale indoor air can accumulate allergens, VOCs from cleaning products and other synthetic chemicals, and odors from cooking or pets, says Neil Riddoch, HVAC expert and owner of Highlander Heating. While air purifiers can help, they don’t remove everything. That’s where opening a window comes in.

Fresh air helps clear out lingering smells, dust, and potentially irritating VOCs, says Mitchell. "I've had allergy-prone clients who saw less congestion and fewer headaches just from regularly airing out their places," he adds. 

Reduced Humidity

Indoor winter air becomes humid from activities such as cooking, showering, and even breathing. When that moisture has nowhere to go, it condenses on cold surfaces (especially windows and walls), creating the perfect conditions for mold growth.

"Four people in a family produce a lot of water vapor just by breathing and cooking," Riddoch explains. "That water will sit on cold surfaces if it has nowhere else to go. This will cause fog and then mold. The best and easiest way to get rid of that extra humidity in the air is to open the windows. This dries out the building, which helps your heating system do its job because dry air is easier to heat than wet air."

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When and How Long to Open Windows in Winter

When opening your windows for ventilation, doing short, intentional bursts is key. The goal isn’t to cool your home (obviously), but to replace stale indoor air with fresh outdoor air. "From what I've seen, five to 10 minutes twice a day is enough for most homes," Mitchell says. "Early morning and early evening work best. If it's windy, you don't need as long. Even once a day helps."

Riddoch recommends using cross-ventilation when possible. This method involves opening windows on opposite sides of the home to improve air circulation. "We use the stack effect or cross-ventilation when we open a window, even if it's only for five minutes," he says. "That old, warm, and muggy air is pushed out much faster than people think because winter air is thick and dry."

When Not to Open Windows in Winter 

There are some situations where opening windows may do more harm than good. And bad outdoor air quality is definitely one of them. "If you live next to a busy highway or in a neighborhood where people smoke a lot of wood, opening the windows might bring in more particles than they remove," Riddoch says.

Extreme temperatures are another time when opening a window might not be the best option. "One time I don't recommend opening windows is during extreme cold snaps, such as when it's under 15 degrees Fahrenheit outside, if your HVAC system isn't strong enough to recover quickly," Mitchell says. "It's also not a good idea in homes with older systems that struggle when exposed to sudden cold air."

In these cases, using filtered mechanical ventilation or exhaust fans to exchange indoor air is a better option. Riddoch adds that homes equipped with HRVs (heat recovery ventilators) or ERVs (energy recovery ventilators) should rely on those systems instead. "They filter the air and return the heat before bringing it in," he explains.

Other Ways to Improve Air Quality 

If you can’t always open your windows, here are a few other things to consider trying:

• Utilize your exhaust fans: The ones in your kitchen and bathrooms are there for a reason. Run them to remove moisture and smells after cooking or bathing.
  
• Keep your HVAC system maintained: Ensuring that filters are regularly changed and the system is working properly helps improve your system's airflow and filtration.
  
• Run a dehumidifier: This is helpful if your air humidity regularly exceeds 50 percent.
• Use products with low VOCs: Whenever possible, select cleaning or home products with fewer VOCs to reduce synthetic chemical buildup in the air.