Generator safety: carbon monoxide, placement, and wet weather
Updated · Reviewed against the current BackupAtlas dataset
Short answer: run a generator outdoors only, at least 20 feet from any door, window, or vent, with the exhaust pointed away from the house — never in a garage, shed, basement, porch, or crawl space, even with doors and windows open or fans running. A built-in CO shutoff sensor is a valuable backstop, not a substitute for correct outdoor placement. Treat every one of these rules as non-negotiable; carbon monoxide from a generator can incapacitate and kill in minutes, and it has no smell to warn you.
Why generator CO is especially dangerous
A gasoline or propane engine produces carbon monoxide as a normal combustion byproduct, and a portable generator's small, unregulated engine produces it in far higher concentrations than a car or furnace. CO is colorless and odorless, binds to blood far more readily than oxygen, and in an enclosed or partially enclosed space can reach lethal concentrations within minutes — long before anyone would notice a symptom like headache or dizziness. According to the CDC, generator-related CO poisoning is a leading cause of non-fire carbon monoxide deaths in the United States, concentrated heavily around storms and outages.
The placement rule, in full
- Outdoors, always. Never run a generator inside a home, garage, shed, basement, crawl space, or other enclosed or partially enclosed structure — a garage door standing open does not make it safe.
- At least 20 feet from the house. This is the widely cited minimum distance from doors, windows, and vents; check your specific generator's manual, since some manufacturers specify more. CO can enter through an open window even from outside that distance if the wind carries it that way — position the exhaust pointing away from the house and away from neighboring homes.
- Never near intakes. Keep the generator clear of HVAC intakes, dryer vents, and anywhere exhaust could be drawn back into the building's air supply.
- Install CO alarms. Battery-backed carbon monoxide alarms on every level of the home are a second line of defense that works regardless of what's happening outside.
What a CO shutoff sensor does — and doesn't — do
Many current-generation portable generators include a CO safety shutoff: a sensor that measures ambient carbon monoxide near the unit and cuts the engine automatically if concentrations rise to a dangerous level, sold under names like CO-MINDER, CO Shield, CO Guard, and CO Sense. These sensors followed CPSC and industry safety pushes and have measurably reduced deaths in enclosed spaces where a generator was run against the rules.
The sensor is a backstop for a mistake already in progress — it does not make it safe to run a generator indoors, in a garage, or close to the house on the assumption that it will shut down before harm occurs. Treat it exactly like a smoke detector: valuable if something goes wrong, never a reason to take the risk in the first place. Models with this feature are listed under generators with CO safety shutoff.
Running a generator in wet weather
Generators are electrical equipment and must stay dry to operate safely — water intrusion into the outlets or control panel creates shock and short-circuit hazards on top of the CO risk. Manufacturers sell listed generator tents and canopies designed for ventilation while shedding rain; an improvised tarp draped over a running generator can trap exhaust and heat instead of venting it, which defeats the purpose. If you don't have a purpose-built enclosure, the safer choice in sustained rain is to place the generator under a carport-style open structure well away from the house, or to accept a pause in generator use, rather than sealing it under a tarp. Keep the unit on dry ground, use a ground-fault-protected cord where required, and never handle the generator, cords, or outlets with wet hands.
The rest of the safety picture
CO placement is the most acute risk, but it isn't the only one. Never refuel a hot generator — gasoline vapor near a hot engine or exhaust is a fire hazard, so let it cool first. Never backfeed a house through a wall outlet; use a transfer switch or interlock installed by a licensed electrician. Use cords rated for the generator's full amperage (see generator cord gauge), and keep the unit clear of flammable materials. When any of this is uncertain for your situation, a licensed electrician and your local fire code are the authorities to check with — this guide is general information, not a substitute for that judgment.