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Every winter, homes become tightly sealed environments where carbon monoxide and smoke don't just linger — they travel. And the system responsible for moving them? Your HVAC.
Most safety guides stop at "install CO detectors and maintain your fireplace." That's important, but it misses a bigger picture. Your forced-air system controls how contaminants circulate, where they concentrate, and how fast they reach dangerous levels. A restricted filter or leaky ductwork doesn't just reduce comfort — it can turn your heating system into a distribution network for the very gases you're trying to avoid.
At Filterbuy, we've manufactured millions of air filters and heard directly from customers dealing with smoke odors, back-drafting fireplaces, and unexplained headaches during heating season. What we've learned is that airflow isn't just an efficiency issue — it's a safety issue. Here's how to make sure your HVAC system is protecting your family this winter, not working against it.
Carbon monoxide and smoke become significantly more dangerous in winter because sealed homes trap contaminants that would otherwise dissipate through open windows and natural ventilation. Your HVAC system plays a central role — it either dilutes and filters these threats or circulates them to every room in your house.
What every homeowner needs to know:
Three things to do right now:
After manufacturing millions of filters and hearing from customers every heating season about the same preventable issues, we can say this with confidence: most winter CO and smoke problems aren't caused by faulty equipment. They're caused by restricted airflow that nobody checked until symptoms appeared.
Carbon monoxide is odorless, colorless, and responsible for hundreds of deaths and thousands of emergency room visits every year in the United States, with the highest concentration of incidents occurring during winter months. Unlike smoke, which you can often see or smell, CO gives no warning until symptoms like headaches, dizziness, and fatigue set in.
During winter, the risk compounds. Furnaces run longer cycles, fireplaces burn more frequently, and homes stay buttoned up tight with minimal fresh air exchange. Smoke from wood-burning stoves, cooking, and even candles doesn't dissipate the way it does in warmer months when windows are open. Instead, it recirculates — and your HVAC system determines where it goes.
Your forced-air heating system is the lungs of your home. When it's working properly, it dilutes contaminants, promotes ventilation, and helps CO detectors pick up threats faster by moving air past sensors. When it's not, the opposite happens.
A clogged or restricted filter forces your system to pull air from wherever it can — including gaps around flue pipes, attached garages, and combustion appliance zones where CO concentrations are highest. This creates negative pressure that can actually draw carbon monoxide into your living spaces. Leaky ductwork compounds the problem by depositing contaminated air into rooms far from the original source, spreading smoke particles and gases throughout the house before anyone notices.
We see this pattern repeatedly in customer feedback during heating season: lingering smoke smells in rooms nowhere near the fireplace, persistent dust despite regular cleaning, and family members experiencing headaches that disappear when they leave the house. In many cases, the root cause isn't the heating appliance itself — it's how the HVAC system is handling the air around it.
Your home often tells you when airflow has become a safety concern. Here are the signals most homeowners miss:
If you notice any combination of these, don't wait. Address your airflow first — it's often the fastest path to resolving the underlying safety issue.
The good news is that most airflow problems have straightforward solutions. Based on what we've learned from over a decade of manufacturing filters and working with HVAC professionals, these are the highest-impact steps homeowners can take:
Change your filters on schedule — or more often in winter. Heating systems run harder and longer during cold months, which means filters load up faster. A filter that lasted 90 days in summer may need replacing in 60 days or less during peak heating season. A restricted filter is the single most common cause of airflow problems we hear about from customers.
Choose the right efficiency level for your system. Higher-MERV filters capture more smoke particles and fine contaminants, but they also require your system to work harder to push air through. The key is matching filter efficiency to what your HVAC system can handle. Most residential systems perform well with MERV 8 to MERV 13 filters — enough to capture smoke particles without starving the system of airflow.
Inspect and seal ductwork. Leaky ducts don't just waste energy — they create pathways for contaminated air to enter and spread. Even small gaps at duct joints can pull in CO from utility closets, attics, or crawl spaces and distribute it throughout your home.
Ensure proper ventilation in high-risk areas. Rooms with gas appliances, fireplaces, or wood stoves need adequate makeup air. If your HVAC system is competing with these appliances for air, negative pressure builds, and back-drafting becomes a real risk.
Schedule a professional HVAC inspection before winter. A technician can check for cracked heat exchangers — one of the most common sources of CO leaks in forced-air systems — along with duct integrity, proper venting, and overall system performance.
Proper airflow is one layer of protection, but it works best alongside these fundamentals:
Install CO detectors on every level of your home, especially near bedrooms and within 15 feet of any fuel-burning appliance. Test them monthly and replace batteries at least once a year. Ensure smoke alarms are positioned correctly and functioning — test those monthly as well. Practice safe fireplace and appliance use by never running unvented gas heaters indoors and always confirming flues are open before lighting a fire. Have an emergency ventilation plan that your household knows: if CO alarms sound, open windows and doors immediately, get everyone outside, and call 911 before re-entering.
Addressing airflow isn't just a winter safety measure — it pays dividends year-round. Properly flowing systems reduce respiratory irritant concentrations, lower the strain on your HVAC equipment (extending its lifespan and reducing repair costs), and maintain more consistent temperatures throughout your home.
From a safety perspective, good airflow means contaminants get diluted and moved past detection sensors faster, giving you an earlier warning when something is wrong. It means your system isn't creating the negative pressure zones that pull CO into living spaces. And it means your filters can actually do their job — capturing smoke particles, dust, and allergens instead of being bypassed by air finding the path of least resistance through gaps and leaks.
Customers tell us that once they get their airflow right, everything else improves: fewer odors, less dust, better comfort, and the peace of mind that comes from knowing their HVAC system is working with them — not against them.
"After manufacturing millions of filters and hearing from customers every winter about smoke odors they can't explain and headaches that disappear when they leave the house, we've learned that airflow isn't just a comfort issue — it's the most overlooked safety factor in winter home protection." — Filterbuy Team
At Filterbuy, we're obsessed with what's in your air — and during winter, that includes invisible threats like carbon monoxide and smoke that most homeowners don't think about until it's too late. After working with millions of customers and hearing firsthand how airflow problems contribute to CO and smoke issues during heating season, we know that good information is your first line of defense.
We've pulled together the most trusted resources from the agencies that set the standard for home safety. Use these to take control of your indoor air and protect what matters most — your family, your home, and the HVAC system that connects them.
Most people don't realize that CO poisoning symptoms look a lot like the flu — and by the time you notice, dangerous levels may already be in your home. The CDC's guide breaks down how carbon monoxide is produced, who's most at risk, and the detection and prevention steps every household should have in place before you turn on the heat.
Why this matters for your air: Carbon monoxide is the definition of an invisible threat. You can't see it, smell it, or taste it — but your HVAC system can move it to every room in your house if airflow isn't managed properly.
Source: Centers for Disease Control and Prevention (CDC) — Carbon Monoxide Poisoning Basics
The EPA explains how CO concentrations develop in indoor environments, with links to OSHA exposure guidelines, CPSC alarm recommendations, and published research on both short-term and prolonged health effects. This is the science behind why sealed-up winter homes are particularly vulnerable.
Why this matters for your air: When we tell customers that airflow is a safety issue and not just a comfort issue, this is the research that backs it up. Tight homes with poor ventilation trap exactly the contaminants this resource helps you identify.
Source: U.S. Environmental Protection Agency (EPA) — Carbon Monoxide's Impact on Indoor Air Quality
epa.gov/indoor-air-quality-iaq/carbon-monoxides-impact-indoor-air-quality
This EPA resource explains how source control, ventilation, and air filtration work together to reduce contaminant levels indoors. One key takeaway: most residential forced-air heating systems don't bring in fresh outdoor air on their own — which makes filter maintenance and duct integrity absolutely critical during winter months.
Why this matters for your air: This is the resource that connects directly to what we see every day at Filterbuy. A clean, properly rated filter is one of the most accessible ways homeowners can improve ventilation efficiency and keep pollutants from recirculating through their homes.
Source: U.S. Environmental Protection Agency (EPA) — Improving Indoor Air Quality
epa.gov/indoor-air-quality-iaq/improving-indoor-air-quality
The CPSC's winter safety guidance covers where CO alarms should be placed, how to maintain fuel-burning appliances, generator safety rules, and the emergency steps to take immediately if an alarm sounds. Think of this as your household's CO action plan.
Why this matters for your air: Detectors and filters work as a team. Your CO alarm tells you when something is wrong — but proper HVAC airflow helps move air past those sensors faster, giving you an earlier warning when contaminant levels rise.
Source: U.S. Consumer Product Safety Commission (CPSC) — Protect Your Family from Carbon Monoxide Poisoning
cpsc.gov/safety-education — Carbon Monoxide Information Center
Nearly half of all U.S. home heating fires occur between December and February. The NFPA provides data-backed safety recommendations for furnaces, fireplaces, wood stoves, and space heaters — along with chimney inspection and maintenance guidance that every homeowner should review before winter starts.
Why this matters for your air: Heating equipment fires produce massive amounts of smoke and toxic gases. Keeping your heating system properly maintained — including regular filter changes — reduces the strain that leads to malfunctions, overheating, and fire risk.
Source: National Fire Protection Association (NFPA) — Home Heating Safety
nfpa.org/education-and-research/home-fire-safety/heating
FEMA's CO prevention page provides free downloadable materials, alarm installation guidelines, and community awareness resources designed to help households detect carbon monoxide early and respond safely. Their guidance on alarm placement is especially valuable for multi-story homes.
Why this matters for your air: We always tell customers that protection works in layers. CO alarms are your detection layer. Proper HVAC airflow and clean filters are your prevention layer. Together, they give you the best chance of catching problems before they become emergencies.
Source: U.S. Fire Administration (FEMA) — Carbon Monoxide Poisoning Prevention
usfa.fema.gov/prevention/life-safety-hazards/carbon-monoxide
The ALA provides health-focused guidance on recognizing CO poisoning symptoms, understanding who is most vulnerable, and taking preventive action — with particular emphasis on protecting children, older adults, and people with existing respiratory conditions.
Why this matters for your air: The symptom patterns the ALA describes — headaches, fatigue, nausea that improve when you leave the house — are exactly what customers report to us when they have restricted airflow and undetected CO movement in their HVAC systems. Knowing these warning signs could save your family's life.
Source: American Lung Association — How to Stay Safe from Carbon Monoxide Poisoning This Winter
lung.org/blog/carbon-monoxide-poisoning-safety
We don't cite these numbers to alarm you — we cite them because after manufacturing millions of air filters and hearing from customers every heating season about the same preventable problems, we know the gap between awareness and action is where the real danger lives.
The CDC reports that each year, more than 400 Americans die from unintentional CO poisoning not linked to fires, over 100,000 visit an emergency department, and more than 14,000 are hospitalized.
What we see at Filterbuy:
This statistic isn't abstract. It's happening in real homes, often because of something as fixable as a dirty filter.
Source: Centers for Disease Control and Prevention — Carbon Monoxide Poisoning Basics
The NFPA reports that nearly half of all U.S. home heating equipment fires — 46 percent — occur during December, January, and February. Between 2020 and 2024, fire departments responded to an average of 37,365 heating fires per year, resulting in 417 deaths, 1,260 injuries, and $1.2 billion in property damage.
What our manufacturing experience tells us:
One filter change. Two minutes of effort. A measurable reduction in system strain and fire risk.
Source: National Fire Protection Association — U.S. Home Heating Fires Peak During Winter Months
nfpa.org/press-room/news-releases/2025
The EPA reports that Americans spend approximately 90 percent of their time indoors, where certain pollutant concentrations are often 2 to 5 times higher than typical outdoor levels.
Why does this change everything about how we make filters:
That shift — from seeing a filter as an HVAC part to understanding it as a frontline health defense — is something we witness with homeowners every day. It's exactly why we're obsessed with making this information accessible.
Source: U.S. Environmental Protection Agency — Indoor Air Quality
epa.gov/report-environment/indoor-air-quality
Most winter safety advice focuses on what to install — CO detectors, smoke alarms, and carbon monoxide monitors. That advice is correct. Those devices save lives every year, and every home should have them.
But after over a decade of manufacturing air filters and working with millions of homeowners, we've reached a conclusion most safety guides don't address: your HVAC system is either your strongest safety asset or your biggest blind spot, and the difference usually comes down to airflow.
A CO detector tells you when something has already gone wrong. Proper airflow helps prevent the conditions that trigger that alarm in the first place.
Detection is reactive. Airflow management is preventive. You need both — but the preventive layer is the one most homeowners overlook entirely.
The same patterns come up year after year:
Almost every time, the root cause isn't a broken appliance or a faulty detector. It's restricted airflow — a filter that should have been changed weeks ago, ductwork leaking into the attic, or blocked vents creating invisible pressure imbalances.
These aren't major renovations. They take minutes and cost a fraction of a single HVAC service call.
If you do one thing before winter hits full stride, make it an airflow check. Your CO detectors and smoke alarms are your last line of defense. Your HVAC airflow is your first. Make sure both are working for you — not against you.
You don't need to overhaul your HVAC system to make your home safer this winter. The most effective steps take minutes, and most cost less than a trip to the hardware store.
Not all filters perform the same during the heating season. Match the MERV rating to your household needs:
Pro Tip: Always confirm your system can handle the MERV rating you choose. A filter too restrictive for your equipment creates the same airflow problems you're trying to prevent. Check your owner's manual or ask your HVAC technician.
We manufacture over 600 filter sizes — including hard-to-find and custom dimensions — so you're never stuck waiting or settling for a fit that's not right. A properly sized, regularly replaced filter is the simplest step you can take to keep airflow working for your family's safety all winter.
Shop HVAC Air Filters at Filterbuy.com
A: This is one of the most common questions we get at Filterbuy. The short answer: no filter can capture CO — it's a gas, not a particle. But the filter's real safety role is maintaining the airflow that keeps CO from becoming dangerous.
Here's what we've learned after manufacturing millions of filters:
The filter doesn't stop CO directly. It prevents the airflow conditions that allow CO to spread.
A: Yes — and this is something we wish more homeowners understood before heating season. CO can enter your air supply through:
Once CO is in the system, your forced-air HVAC pushes it to every connected room. We hear from customers every winter who can't explain fumes or headaches in rooms far from the furnace. The answer is almost always the ductwork.
Two things reduce this risk most: sealed ducts and a properly maintained filter.
A: The standard 90-day schedule doesn't hold up during heating season. Based on millions of filter orders and direct customer feedback, most homes need replacement every 30–60 days in winter.
Why winter is different:
Our recommendation:
We see the pattern in our own order data — customers on a summer schedule are the ones calling about restricted airflow and strange odors in January.
A: After over a decade of manufacturing every MERV rating and working with HVAC professionals, our answer: MERV 11 to MERV 13 for most residential systems.
Here's the breakdown:
The mistake we see most often: customers upgrading to MERV 13 in a system designed for MERV 8, then experiencing worse airflow than before.
The rule we tell every customer:
A: After years of hearing from customers during heating season, we've found the earliest signs are the ones most easily dismissed. Here's what to watch for:
Our advice to every customer: don't ignore the combination.
These are the situations where minutes matter.
Your HVAC system's airflow is the difference between a home that's protected from CO and smoke hazards and one that's quietly circulating them. Find your filter size at Filterbuy.com and take the simplest, most effective step toward safer winter air today
