Carbon Monoxide Safety at Home

Carbon monoxide is an invisible, odorless gas produced whenever fuel burns incompletely, and at high levels it can be deadly within minutes. You cannot see it, smell it, or taste it, so working CO alarms are the only reliable warning you will get. Washington requires them in nearly all homes. This guide covers where CO comes from, where alarms belong, what the symptoms look like, and exactly what to do when an alarm sounds.

What is carbon monoxide and where does it come from?

Carbon monoxide, or CO, forms when any fuel burns without enough oxygen: natural gas, propane, wood, gasoline, charcoal, or oil. A properly installed and properly vented appliance produces very little and sends it outside. Problems start when combustion goes wrong or venting fails. In a typical Puget Sound home, the sources to know are:

• Gas furnaces: a cracked heat exchanger, blocked flue, or poor combustion can push CO into the ductwork that feeds every room.
• Gas water heaters: a blocked or disconnected vent, or backdrafting caused by strong exhaust fans depressurizing the house, can spill flue gases indoors.
• Gas ranges and ovens: these vent into the kitchen, so a poorly tuned burner or an oven used for space heating raises indoor CO directly.
• Attached garages: a car idling in the garage, even briefly with the door open, can drive CO into the house through the shared wall and door. Never warm up a vehicle in an attached garage.
• Fireplaces, generators, and grills: wood stoves with poor draft, portable generators run too close to the house, and any charcoal or gas grill used indoors are recurring causes of CO deaths reported by the CPSC. Generators belong far from doors, windows, and vents, and grills never come inside.

What does Washington require for CO alarms?

Washington state law requires carbon monoxide alarms in virtually all residences. They are required in new construction, in all rentals, and in existing owner-occupied homes at the point of sale. The standard is alarms outside each sleeping area and on every level of the home, including basements. Combination smoke and CO units are allowed and are a practical way to meet both requirements at once. If your home predates these rules and has never been updated, you are likely under-protected, particularly if you have any gas appliance or an attached garage. Our overview of smoke and CO detectors covers the options, including hardwired and interconnected units that all sound together.

Where should alarms go, and how long do they last?

Placement rules are simple. Put a CO alarm in the hallway outside every bedroom cluster, at least one on every level, and follow the manufacturer's height guidance. Keep alarms at least 10 to 15 feet from fuel-burning appliances and away from bathrooms, so normal humidity and brief combustion at startup do not trigger nuisance alarms that tempt you to pull batteries.

CO sensors wear out. Most CO alarms last 5 to 7 years, and newer models up to 10; the replacement date is printed on the back of the unit. An expired alarm can look and chirp like a healthy one while its sensor is dead. Check the dates on every alarm in your house this week. If any lack a date, they are old enough to replace. Test buttons monthly, and replace batteries when you change your clocks unless the unit has a sealed 10 year battery.

What are the symptoms of CO exposure?

Low-level CO poisoning feels like the flu without the fever: headache, fatigue, dizziness, nausea, and shortness of breath. Higher levels bring confusion, blurred vision, and loss of consciousness. Two patterns should raise your suspicion. First, symptoms that improve when you leave the house and return when you come back. Second, multiple people, including pets, feeling ill at the same time in the same building. Infants, older adults, pregnant women, and anyone with heart or breathing problems are affected at lower levels. If you notice either pattern, treat it as a CO event even if no alarm has sounded, and get the home tested.

What should you do when a CO alarm goes off?

1. Take it seriously every time. Do not assume a false alarm and do not just open a window and silence it.
2. Get everyone outside to fresh air immediately, including pets. Count heads.
3. Call 911 from outside. The fire department can meter the actual CO level in the house.
4. Do not re-enter until responders say the home is clear.
5. If anyone has symptoms, say so clearly and get medical attention. CO poisoning is confirmed with a blood test, not a guess.
6. Before using the fuel-burning appliances again, have them inspected and the source identified. An alarm that fired had a reason, even if the level dropped by the time responders arrived.

Why do venting and combustion testing matter?

Alarms are the last line of defense. The first line is making sure your appliances burn cleanly and vent completely outdoors. That is why a proper furnace tune-up includes checking the heat exchanger, verifying draft, and testing combustion rather than just swapping a filter. Our seasonal tune-up visits do this on every gas furnace we service, and our heating team treats any measurable CO spillage as a stop-work safety issue, not a note on an invoice. The same logic applies to gas piping itself: leaks, corrosion, and amateur connections create both fire and CO risks, which is covered in our guide to gas line safety basics. If your water heater is gas-fired, its vent deserves the same annual attention as the furnace flue.

Common questions

Do I need CO alarms if my home is all electric?

Washington's requirements apply broadly, and there are good reasons to keep alarms even without gas service: an attached garage, a wood stove or fireplace, or a portable generator during an outage can all produce CO. If your home has none of these and no fuel-burning anything, your risk is much lower, but alarms are cheap insurance and required at sale in any case.

Why does my CO alarm chirp once every minute?

A single repeating chirp usually means a low battery or an expired unit, while a repeating four-beep pattern typically means CO is detected. Patterns vary by brand, so check the label on the back. If there is any doubt about whether it is a fault or a detection, leave and call 911 rather than guessing.

Where should I not put a CO alarm?

Avoid mounting alarms directly beside fuel-burning appliances, inside bathrooms, next to windows or supply registers, or in dead-air corners. All of these spots either trigger nuisance alarms or delay real ones. Follow the manufacturer's placement instructions that come with the unit.

Can my HVAC system spread CO through the house?

Yes. A furnace with a compromised heat exchanger or a backdrafting appliance near a return duct can distribute CO to every room quickly. That is exactly why alarms belong on every level and outside every sleeping area, and why combustion testing is part of responsible furnace service.

What to do next

This week: check the manufacture date on every smoke and CO alarm in your home, test each one, and make sure there is an alarm outside every sleeping area and on every level. This season: if you have any gas appliance and it has not been inspected in over a year, schedule a combustion safety check. Eco's licensed team handles detector installation and heating system safety inspections across the Puget Sound area. Book online or call (206) 970-1031, 6 AM to 6 PM every day.