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Run a portable generator at least 20 feet from the house, outdoors in open air, with the exhaust pointed away from every door, window and vent. That figure comes from the US Consumer Product Safety Commission, and it is a minimum rather than a recommendation. Never run a generator in a garage, a basement, a crawlspace, a shed, or under a carport, an open porch or a deck — an open door does not make an enclosed space safe. Fit carbon monoxide alarms on every level of the home, and treat 25 to 30 feet as better if your lot allows it.
Why is the distance 20 feet?
Because a portable generator emits carbon monoxide at a rate most people badly underestimate. The CPSC states plainly that a single portable generator can produce as much carbon monoxide as hundreds of cars. In an enclosed or partly enclosed space that concentration becomes lethal within minutes, and even in open air it takes distance and moving air to dilute it below dangerous levels near the house.
Twenty feet is the point at which normal outdoor air movement reliably disperses exhaust before it can accumulate against a wall or find its way through a gap into the building envelope. Closer than that, exhaust can be drawn in through a window, a soffit vent, a dryer vent, a crawlspace opening, an air conditioning intake, or simply the gaps around a door — and a house under negative pressure from a running furnace fan pulls harder than most people imagine.
The reason this specific hazard kills so consistently is that carbon monoxide provides no warning of any kind. It is colorless, odorless and tasteless. The early symptoms — headache, dizziness, nausea, confusion — read as exhaustion or stress during the disruption of a storm, and people who lie down to rest frequently do not get up. More than 100 US deaths a year are linked to portable generator carbon monoxide, and the toll spikes in the days after major storms.
Where you must never put a generator
| Location | Safe? | Why |
|---|---|---|
| Attached garage, door open | No | Ceiling and walls hold exhaust; the door does not fix it |
| Detached garage or shed | No | Same enclosure problem, plus a fire risk from stored fuel |
| Carport or open porch | No | A roof is enough to trap exhaust against the house |
| Under a deck or stairs | No | Traps exhaust and heat directly beneath living space |
| Basement or crawlspace | No | Fatal within minutes |
| Inside an RV, van or tow vehicle | No | A leading cause of generator CO deaths |
| Against an exterior wall | No | Exhaust washes along the wall and into openings |
| Beside a window or dryer vent | No | Direct path into the building |
| Open yard, 20+ feet, exhaust pointed away | Yes | The only correct placement |
How much does exhaust direction matter?
As much as the distance, and sometimes more. A generator 20 feet away with its exhaust aimed at an open bedroom window is a worse placement than one 20 feet away pointing into open yard. Point the exhaust away from the house, away from any door, window, vent, soffit, dryer outlet or air conditioner intake, and away from your neighbor's openings too — carbon monoxide does not respect a property line, and neighbors have died from generators they did not own.
Check the wind on the day. A steady breeze pushing exhaust toward the building cancels a good part of the benefit of the distance, and the correct response is to move the generator further out or reposition it, not to accept the orientation. Point the exhaust away from anything combustible as well: a generator muffler runs hot enough to ignite dry leaves, mulch or long grass.
Do I still need carbon monoxide alarms?
Yes, and they are not optional if you own a generator. Correct placement reduces risk; alarms are what catch the situation where placement was not as good as you thought — a wind shift, a vent you did not know about, a neighbor's generator, or a family member who moved the machine closer because of rain.
Fit battery-operated or battery-backed CO alarms on every level of the home and outside each sleeping area, and test them before storm season rather than during it. Alarms have a service life, typically five to ten years depending on the sensor, and there is a date printed on the housing — an expired alarm is a decoration. If a CO alarm sounds, get everyone outside into fresh air immediately and call 911 from outside. Do not go back in to investigate or to open windows.
What about rain?
Generators must be kept dry — water in the alternator or the control panel is both a shock hazard and a machine-killer — but the way you do it matters enormously. Use a purpose-made generator running cover or an open-sided canopy designed for the job: these keep rain off the top while leaving every side completely open to airflow. What you must never do is drape a tarp over a running machine, put it in a tent, roll it into a shed, or tuck it under a deck. Every one of those turns a rain problem into a carbon monoxide problem.
Other wet-weather points: never operate a generator standing in water or touch it with wet hands, raise it on a pallet or blocks if the ground floods, and use only outdoor-rated extension cords with an intact ground pin.
The other rule that kills people
Distance protects you from carbon monoxide. Nothing about distance protects utility line workers from backfeeding. Never plug a generator into a wall outlet to power your house. Doing so energizes your home wiring and pushes power back through the transformer onto the neighborhood lines, where a line worker who has tested that circuit dead can be electrocuted. It can also destroy the generator and start a fire when grid power returns out of phase.
The only correct method is a manual transfer switch or an approved interlock kit, installed at the service panel by a licensed electrician with a permit. Our standby generator and transfer switch guide covers the options and realistic costs. Until that is installed, run appliances directly from the generator using outdoor-rated extension cords.
Where to go next
The full carbon monoxide picture, including which generators have automatic CO shutdown sensors, is in generator carbon monoxide safety. For run-time limits and refueling during a long outage see how long a generator can run continuously. Our ranked best portable generators flags which models carry CO shutdown as standard. Everything sits under the power tools and workshop hub.
Sources: US Consumer Product Safety Commission Carbon Monoxide Information Center; CDC, carbon monoxide poisoning basics; Ready.gov, power outages.
We never buy or physically handle the equipment we rank — our recommendations come from aggregated owner reviews and expert consensus, and the method is on how we rank.