Carbon monoxide safety — sources detection and what to do

This article is for educational purposes only and is not a substitute for professional advice. Local codes, regulations, and best practices vary by region.

Carbon monoxide is an invisible, odorless gas created when fuel burns incompletely. Your furnace, water heater, and car all produce it as a byproduct. Normally it vents safely outside. If vents are blocked or equipment malfunctions, it accumulates inside your home. Breathing it prevents your blood from carrying oxygen. Enough exposure causes death. Smaller exposures cause flu-like symptoms (headache, nausea, dizziness) that worsen over hours.

The good news is detection and prevention are straightforward. CO detectors alert you before dangerous levels develop. Annual furnace maintenance and proper venting prevent most problems.

Common Sources

Gas furnaces are normal CO sources. When working properly, CO vents out the chimney. When the furnace is older, venting might be compromised, allowing CO to leak into your home.

Gas water heaters produce CO similarly. A venting problem means CO seeps indoors.

Gas stoves and ovens produce CO if you use them to heat your home (never do this). Even normal use produces some CO, which is why kitchens need ventilation.

Fireplaces and wood stoves need proper venting. A blocked or damaged chimney traps smoke (and any CO) inside.

Cars running in attached garages are a major risk. Exhaust is rich in CO. If the door from the garage to your home isn’t sealed or is open, CO seeps inside.

Generators running in basements, garages, or near windows are dangerous. Portable generators must run outside, far from windows and doors. Even the wind can carry exhaust toward an open window.

Blocked or damaged chimneys, vents clogged with snow or leaves, or drying clothes on a dryer vent can block venting pathways, causing CO to back up into the home.

Detection

CO detectors are inexpensive ($30 to $100 each). They should be placed in bedrooms (you’re at risk when you’re sleeping) and common living areas. At minimum, one near the garage if you have an attached garage, and one outside the bedroom area.

Detectors sound an alarm when CO levels exceed safe ranges. Most have a digital display showing current CO levels.

Testing: Press the test button monthly. Confirm the alarm sounds. If it doesn’t, replace the battery or the detector.

Batteries should be replaced annually (similar timing to smoke detectors). Detectors themselves typically last 5 to 7 years.

What to Do If An Alarm Sounds

Leave the house immediately. Don’t try to investigate or shut things off. Get everyone outside and call the fire department from outside.

The fire department can detect CO with specialized equipment and identify the source.

Never re-enter the house until professional firefighters have confirmed it’s safe and identified the problem.

Prevention and Maintenance

Annual furnace inspection (part of your routine HVAC maintenance) catches venting issues, corroded heat exchangers, and other problems before CO develops.

Annual water heater inspection for proper venting.

In winter, clear snow and debris from outdoor vents and chimney openings. A blocked vent forces CO inside.

Check that dryer vents aren’t clogged. A clogged vent backs up.

Keep your garage door closed as much as possible. If you must run your car in the garage (only briefly for pulling in/out), open the main garage door immediately.

Never use your gas oven or stove to heat your home. Besides CO risk, it’s inefficient and expensive.

Peace of Mind

A properly vented furnace and water heater, combined with working CO detectors, essentially eliminate CO risk. The combination is simple: annual professional furnace/water heater service ($150 to $300 annually) and detectors ($80 to $200 upfront).

CO poisoning is a real risk but rare in homes with basic prevention and detection. Don’t obsess, but don’t ignore it either.

© The Whole Home Guide