Top 5 Things That Can Worsen Indoor Air Quality in Winter (and How to Fix Them)

When temperatures drop, our cozy homes become our sanctuaries. But as windows close and heating systems kick into high gear, indoor air becomes trapped, stale, and often more polluted than the air outside.

From hidden mold spores to gases like radon, winter creates the perfect storm for poor indoor air quality. The result? Headaches, allergies, fatigue, or that “stuffy” feeling you can’t quite shake.

Before you hunker down for the season, here are five common culprits that could be affecting your air and what you can do to fix them.

1. Poor Ventilation Trapping Indoor Pollutants  

When homes are sealed tight to conserve heat, air has nowhere to go and neither do pollutants. Everyday activities like cooking, cleaning, and even breathing release moisture and microscopic particles (VOCs – link) that linger in the air. Add in radon gas seeping through foundations or off-gassing from building materials, and your home’s air can quickly become stagnant and unhealthy.

How to fix it?

• Open windows for a few minutes each day, even in winter, to refresh your indoor air.

• Use an HRV (Heat Recovery Ventilator) or ERV (Energy Recovery Ventilator) to continuously circulate fresh air without losing heat.

• Have an indoor air quality inspection to identify lingering issues like high VOC levels, radon buildup, or even mold spores.

2. Humidity That Encourages Mold Growth

Humidity might make the air feel cozy, but too much of it creates the perfect breeding ground for mold. Everyday activities such as showers, cooking, and even drying clothes indoors, can quickly raise indoor humidity. When that moisture clings to cold surfaces like windows and walls, mold spores thrive.

How to fix it?

• Keep indoor humidity between 30–50% (a simple hygrometer can help).

• Use bathroom and kitchen exhaust fans while cooking or showering.

• Run a dehumidifier in damp areas like basements or laundry rooms.

• Inspect for condensation or damp spots (they’re early warning signs of hidden moisture problems)

3. Heating Systems Circulating Dust and Allergens  

When furnaces fire up after months of sitting idle, they can push dust, pet dander, and other allergens through your home’s ducts. If filters are clogged or ducts are dirty, your heating system could be recirculating more than just warm air.

How to fix it?

• Replace furnace filters every 1–3 months.

• Have your ducts cleaned or inspected at least once a year.

• Schedule annual HVAC maintenance to ensure systems are running safely and efficiently.

• Consider using HEPA filters to trap smaller particles and improve overall air quality.

4.  Combustion Byproducts Form Fireplaces and Space Heaters

There’s nothing like a crackling fire on a cold night to warm you up, but fireplaces, gas stoves, and space heaters can release combustion byproducts (like carbon monoxide and nitrogen dioxide) and fine particulate matter that can irritate lungs and cause long-term health issues.

How to fix it?

• Install carbon monoxide detectors on every level of your home.

• Keep chimneys clean and professionally inspected before each winter.

• Make sure all fuel-burning appliances are properly vented.

• Avoid using unvented space heaters indoors

5. Hidden Hazards Lurking on Your Home

Winters closed-up environment can trap gases and fibres that would otherwise disperse. Radon, a common and dangerous naturally occurring radioactive gas, is one of these hazards you should be aware of. Meanwhile, older materials can release asbestos fibres if disturbed, and hidden mold behind walls can continue to grow unnoticed.

How to fix it?

• Test for radon every 2–3 years, especially during winter when levels can spike.

• Inspect and test aging materials like insulation, tiles, and drywall for potential asbestos risks.

• If you suspect hidden mold, call a certified remediation or air quality professional (like the experts at got mold?™) for proper testing and remediation services.

Winter is when we spend the most time indoors, and when our air quality matters most. Between heating systems, lack of ventilation, and increased humidity, small problems can compound quickly. Taking a few proactive steps now can help protect your health, improve comfort, and even extend the life of your home systems.

If you’ve noticed musty smells, persistent dust, or unexplained headaches this season, it might be time to look closer at your indoor air. Start with reaching out to our team of indoor air quality professionals to get an accurate assessment to start your journey towards breathing in cleaner air this season.

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