Generator Carbon Monoxide Safety

Every storm season, people die running generators. Almost always from carbon monoxide, and almost always because the generator was somewhere that seemed ventilated enough.

Generator CO safety

Carbon monoxide is odourless and gives no warning. An attached garage with the door up is still an enclosed space — CO accumulates and migrates into the house. The combination that saves lives is distance plus working CO alarms inside.

What makes it dangerous

Carbon monoxide is colourless and odourless. There is no sensory warning. You don't smell it, you don't taste it, and the first symptoms resemble tiredness.

A generator produces a great deal of it. A portable generator's engine emits far more CO than a car — the CDC has described a single generator's output as comparable to hundreds of idling cars. It accumulates fast in any confined space.

It incapacitates before it kills. High concentrations cause confusion and unconsciousness quickly. People often can't act on symptoms once they notice them, which is why "I'd move it if I felt unwell" isn't a plan.

The rules

Outdoors only. Never inside a house, garage, basement, crawl space, shed, carport, breezeway, or any enclosed or partially enclosed space.

At least 20 feet from the building, per common manufacturer and safety-agency guidance. Further is better.

Exhaust directed away from doors, windows, and vents — including your neighbour's.

Not under an overhang, deck, or awning, where exhaust collects rather than dispersing.

Not near a window air conditioner, which will draw exhaust straight into the room.

Never in a partially enclosed space — this includes a garage with the door open, a carport, and an alcove.

Why isn't an open garage door enough?

This is the specific misconception that kills people, so it's worth being direct.

A garage with the door open is still a partially enclosed space. Air doesn't sweep through it — CO accumulates, especially near the back and near the ceiling, and it migrates into the house through the connecting door, gaps around it, and shared ductwork.

Adding a fan doesn't fix it. Opening a second door doesn't fix it. The generator does not belong in the garage under any configuration.

The same applies to sheds, carports, covered patios, and "just inside the door out of the rain".

Rain and weather

The reason people move generators into garages is weather. The correct answer is a generator cover or canopy designed for running operation — an open-sided structure that keeps rain off while allowing full airflow and exhaust dispersal.

Never a tarp draped over a running generator, and never an enclosed structure.

See running a generator in rain and snow.

CO alarms

Install working CO alarms on every level of the home and near sleeping areas. Battery-powered or with battery backup — a hardwired-only alarm is useless in exactly the situation you need it.

Test them before storm season, not during.

Replace them on schedule. CO alarm sensors have a finite life, commonly 5 to 10 years depending on the model, and expired units may not detect anything. Check the date on the back.

Many newer portable generators include CO shutoff sensors that stop the engine when CO builds up nearby. This is a genuinely valuable feature and worth prioritizing when buying — but it is a backstop, not permission to place the generator badly.

Symptoms

CO poisoning resembles flu, which is part of why it's missed:

• Headache
• Dizziness, weakness
• Nausea, vomiting
• Confusion, poor coordination
• Shortness of breath
• Loss of consciousness

The tell: several people, or people and pets, feeling unwell at the same time — and improving when they go outside.

If you suspect it: get everyone outside immediately, into fresh air. Call emergency services from outside. Do not go back in to open windows or switch anything off. Do not re-enter until responders say it's safe.

Other generator hazards worth naming

Electrocution. Never operate a generator in wet conditions without protection, never touch it with wet hands, and never run cords through standing water. Portable generators should have GFCI-protected receptacles for cord-connected loads.

Backfeed. Connecting a generator to house wiring through a receptacle energizes the utility line and can kill line workers. See backfeeding dangers.

Fire. Never refuel a running or hot generator — spilled gasoline on a hot exhaust ignites. Shut it down and let it cool. Store fuel in approved containers, away from the house and any ignition source. See gasoline storage and stabilizer.

Burns. The exhaust and muffler stay hot long after shutdown.

A pre-storm checklist

• CO alarms tested, batteries fresh, within service life
• Generator placement planned — 20+ feet, exhaust direction, not under anything
• Running cover or canopy available if weather is expected
• Cords outdoor-rated and correctly sized
• Fuel stored safely, stabilized, in approved containers
• Everyone in the household knows where the generator goes and where it doesn't

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• IRC R315 — carbon monoxide alarm requirements in dwellings
• UL 2034 — residential CO alarm standard
• ANSI/PGMA G300 — portable generator safety, including CO shutoff

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.

Where to go next

• Running a generator in rain and snow
• How to connect a generator to your house
• Generator maintenance schedule
• Size it properly: generator sizing calculator

More in our generator and backup power guides.