Carbon Monoxide in Your Home

Furnaces, water heaters, gas stoves, fireplaces, attached garages — most rooms in a typical home are near something that can produce carbon monoxide if it malfunctions or vents improperly. Knowing the signs of carbon monoxide in your home is critical because CO has no smell and early symptoms mimic the flu. This guide walks through the most common household sources — from your furnace and water heater to your garage — explains the warning patterns that suggest a problem, and provides a practical carbon monoxide (CO) safety checklist you can act on today.

This is general safety information — not medical or legal advice. If you suspect active exposure or severe symptoms, move to fresh air and contact emergency services.

Quick Safety Summary

Top home sources: furnaces/boilers, water heaters, gas stoves/ovens, fireplaces, and attached garages.
Portable generators during outages are a leading cause of fatal CO poisoning — outdoors only, far from buildings.
Warning pattern: "flu-like" symptoms that improve outdoors and affect multiple people or pets at once.
If a CO alarm sounds: leave immediately, call for guidance/air testing, and don't re-enter until cleared.
Annual appliance inspection + working CO alarms on every level are your best defense.

Where CO Comes From at Home

CO is produced when carbon-based fuels burn incompletely. In a well-installed system, combustion gases are vented outdoors. Problems occur when venting is blocked, equipment is damaged or misadjusted, or a device is used in a confined space. Because CO mixes with air and has no smell, alarms and safe habits are critical layers of protection.

Understanding how to prevent carbon monoxide in home environments starts with understanding airflow. In a properly functioning home, combustion gases travel up through vents, flues, and chimneys and exit the building. But several factors can disrupt this process. Tight weatherization (sealed windows, insulation upgrades) can reduce the air supply that combustion appliances need, leading to incomplete burning. Running multiple exhaust fans — kitchen range hoods, bathroom fans, clothes dryers — at the same time can create negative air pressure inside the house, which can pull combustion gases backward through vents and into living spaces (a problem called back-drafting). Even something as simple as a strong wind from the wrong direction can temporarily overpower a chimney's draft. The lesson: ventilation isn't just about opening windows — it's about making sure the entire system of air supply, combustion, and exhaust works together.

Common Sources of Carbon Monoxide in the Home

The most common household CO sources are fuel-burning appliances and equipment. Risk is higher when maintenance is neglected, venting is blocked, or appliances are used in ways they were not designed for.

Furnaces, Boilers, and Water Heaters

Heating systems and water heaters can produce dangerous CO levels if burners are not operating correctly or if exhaust cannot vent outdoors. If you suspect a problem, stop using the appliance and arrange a professional inspection.

Stoves, Ovens, and Gas Ranges

Gas stoves and ovens can produce CO, especially with poor ventilation or abnormal combustion. Never use a gas oven to heat a room.

Fireplaces and Wood Stoves

Fireplaces can become CO sources if the chimney/flue is blocked, the damper is closed, or exhaust back-drafts into the room. Soot, staining, or persistent draft problems justify professional evaluation.

Other Fuel-Burning Appliances

Gas dryers and other fuel-burning equipment can also contribute if venting is incorrect.

The Garage Factor

An attached garage is a common "hidden" pathway for CO into a home. Vehicle exhaust can build up and seep through doors, walls, and ventilation paths — even with the garage door open. Never idle a vehicle in an attached garage, and avoid running gasoline-powered tools in enclosed garage spaces.

More on vehicle scenarios: Carbon monoxide in your car.

The risk from an attached garage deserves extra emphasis because it catches people off guard. Many homeowners don't realize that the wall between the garage and the house is rarely airtight — gaps around doors, electrical outlets, plumbing penetrations, and shared attic spaces all provide pathways for exhaust to migrate into living areas. Even after the car has been moved outside, residual CO can linger in the garage and continue seeping into the house. Running gasoline-powered lawn equipment, snow blowers, or pressure washers in the garage creates the same risk as idling a car. If your home has an attached garage, treat it as a zero-tolerance zone for engine exhaust: start vehicles and equipment outside, keep the connecting door closed and sealed, and ensure CO alarms are installed on the wall nearest the garage on the living side.

Generators, Grills, and Outage Scenarios

Portable generators produce large amounts of CO and are a leading cause of fatal poisonings during storms and power outages. Generators must be used outdoors only, far from buildings and openings. Never use a generator in a garage, basement, crawlspace, or near windows and doors.

Charcoal grills and camping stoves can also produce deadly CO. Never use them indoors, in garages, or in enclosed/semi-enclosed areas.

Apartments and Shared Buildings

In multi-unit buildings, CO can sometimes affect more than one apartment due to shared mechanical rooms, venting paths, or attached garages. If your alarm sounds or you suspect exposure, follow emergency steps first. Then notify building management so qualified inspection can include shared equipment and venting.

Ventilation failures in shared buildings deserve special attention. When a building's central exhaust system malfunctions or is undersized, combustion gases from one unit's appliances can spill into common hallways or adjacent apartments. In buildings with shared boiler rooms, a single venting problem can affect the entire structure. Negative pressure from rooftop exhaust fans or corridor pressurization systems can pull flue gases backward into individual units. If you notice recurring condensation on your windows during heating season, persistent stuffiness that doesn't improve with window ventilation, or if your CO alarm triggers without an obvious source in your unit, the problem may be building-wide. Report these patterns to management and request professional testing of shared mechanical equipment and ventilation systems.

Warning Patterns and Clues

CO exposure often announces itself through context rather than a smell. Warning patterns include:

Multiple people feel unwell at the same time indoors (headache, dizziness, nausea, unusual fatigue).
Symptoms improve when you leave the building and return when you come back.
Symptoms appear when heat, hot water, or a fireplace is running.
Pets appear unusually lethargic or unsteady at the same time.
Soot/staining around appliances or vents, recurring pilot issues, or poor draft signs.

These clues are not proof. The safe response is to leave to fresh air and get professional guidance/testing when exposure is possible.

What to Do If You Suspect Carbon Monoxide in Your Home

If your CO alarm sounds or the situation fits a high-risk pattern, get everyone out to fresh air without delay and call your fire department or emergency services for air testing. Do not go back inside until the building has been professionally cleared. Once safe, arrange inspection of fuel-burning appliances and venting before using them again, and verify your CO alarms are up to date.

Full emergency response steps: What to do if you suspect a carbon monoxide leak.

Protecting Your Home From CO

CO prevention is practical: use working alarms, maintain fuel-burning appliances, keep venting clear, never run generators or grills indoors, and never idle vehicles in attached garages.

Full checklist: Prevention of carbon monoxide poisoning.

Home CO Safety Checklist

CO alarms installed on every level and near sleeping areas.
CO alarms tested monthly; batteries replaced as needed; units replaced at end-of-life.
Furnace/boiler inspected and serviced annually by a qualified technician.
Water heater venting checked for proper connection and draft.
Fireplace chimney/flue inspected and cleaned annually.
Gas stove/oven: range hood used; never used for room heating.
Attached garage: vehicles never idled inside; door between garage and home kept closed.
Generator: used outdoors only, 20+ feet from building, exhaust directed away.
Vents and exhaust paths checked for blockages (snow, debris, nests) seasonally.
Space heaters: only models rated for indoor use; manufacturer instructions followed.

Sources & References

Frequently Asked Questions

How do I know if there is carbon monoxide in my home?

A CO alarm is the clearest warning. Other clues include flu-like symptoms that improve outdoors, multiple people feeling sick indoors, and symptoms linked to running fuel-burning appliances.

Can I smell carbon monoxide in my house?

No. CO is odorless. You cannot rely on smell to detect it.

How often should home fuel-burning appliances be inspected for CO safety?

At least once a year by a qualified technician. Annual inspections of furnaces, boilers, water heaters, and chimneys are a key prevention step.

Can a gas stove cause carbon monoxide problems?

It can contribute, especially with poor ventilation or abnormal combustion. Never use a gas oven to heat a room.

Is it safe to run a car in an attached garage with the door open?

No. CO can build up and seep into living spaces even with the garage door open.

Can carbon monoxide come from a neighbor's apartment?

In some buildings, shared venting or mechanical areas can affect multiple units. Follow emergency steps and notify management/responders.

Where does carbon monoxide most commonly come from at home?

Furnaces/boilers, water heaters, stoves/ovens, fireplaces, attached garages, and generators used improperly are common sources.

Last updated: February 15, 2026