Generator Safety Checklist: 9 Rules That Prevent CO Poisoning
UHBy UsefulHow Editorial Team·Published Jul 23, 2026·Updated Jul 23, 2026·6 min read
Quick AnswerRun a portable generator outside only, at least 20 feet from the house, with the exhaust pointed away from windows and doors. Never in a garage — even with the door open. Let it cool before refueling, never backfeed power into your walls, and keep working CO alarms on every level. Those habits prevent nearly every generator death.
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Carbon monoxide is why generators kill. The gas has no smell and no color, a running generator puts out enough of it to fill an enclosed space with lethal air in minutes, and the first symptoms — headache, dizziness, nausea — feel like the flu, so people lie down instead of going outside. Nearly all of it happens during outages, at night, with the unit in a garage or sitting just outside an open window. The nine rules below are the whole defense, and none of them are hard.
Where It Runs — Rules 1–3
- Rule 1: Outdoors only. Never a garage, basement, crawl space, shed, or screened porch. Not "just while it rains," not "just for a few minutes."
- Rule 2: At least 20 feet from the house. Exhaust pointed away from windows, doors, and intake vents. Twenty feet is a floor, not a target — if a breeze is blowing toward the house, give it more.
- Rule 3: A rain plan that stays outside. Use a canopy made for generators or an open-sided cover, on dry ground. Never touch the unit with wet hands or while standing in water.
Fuel and Fire — Rules 4–5
- Rule 4: Let it cool completely before refueling. Gasoline vapor and a hot engine are a fire waiting for a spark. Shut it down, wait, then fill. Store fuel in approved containers, away from the generator and out of the living space.
- Rule 5: Keep the area around it clear. The muffler gets hot enough to ignite dry leaves, cardboard, and grass. Give it a few feet of nothing on every side.
Power and Cords — Rules 6–7
- Rule 6: Never backfeed. No homemade double-ended cord plugged into a dryer or range outlet. Backfeeding can send power out onto utility lines and kill a line worker trying to restore your street — and it's against code everywhere. Either plug appliances directly into the generator, or have an electrician install a transfer switch. Those are the only two safe ways to use one.
- Rule 7: Use cords that match the load. Outdoor-rated, heavy-gauge, undamaged. A frayed or light-duty indoor cord overheats quietly under a real load. And count your watts: motors like a fridge, furnace blower, or well pump can briefly draw two to three times their running watts when they start.
Alarms and People — Rules 8–9
- Rule 8: Working CO alarms on every level and outside each sleeping area, with battery backup. Your nose cannot detect this gas; an alarm is the only sense that can. Our guide to where CO detectors go and how many you need covers placement. Test them before storm season, not during the outage.
- Rule 9: At the first alarm — or the first headache or dizziness — everyone goes outside. Call 911 from out there. Don't go back in to shut the generator off or throw open windows. Firefighters carry the breathing gear for that job.
The garage myth kills people every storm season"Door open, just a few feet inside" is the setup investigators find again and again. An open garage door does not vent CO fast enough; the gas pours through the door into the house and lingers for hours. If theft or noise is why the generator keeps creeping closer to the house, solve that problem instead — chain the unit to something solid, out at its 20 feet. Outside and 20 feet away has no weather exceptions.
Mistakes That Show Up in the Reports
Running it on the porch "because it's covered." A porch is a few feet from windows and often half-enclosed. It's the garage mistake with better scenery.
Refueling hot, at midnight, by flashlight. The outage has hours to run and so does your patience. Shut it down, let it cool, then fill it.
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Treating a CO alarm as permission. The alarm is the backup system for when a rule already failed. It is not a license to run the generator closer.
Plugging everything in at once. Bring loads on one at a time, biggest motor first. Slamming the unit with everything at once stalls the engine and can damage the appliances you're trying to protect.
The Bottom Line
Generators don't kill through defects. They kill through placement and habits — and both are entirely in your control. Outside only, 20 feet away, exhaust pointed off into the yard, cool before fuel, no backfeeding, alarms that work. Print the checklist and keep it with the machine; pair it with our power outage checklist for the rest of the outage routine, and run through the generator rules again each time you do your winter storm prep — before the power goes out, not after.
Frequently Asked Questions
Can I run a generator in the garage with the door open?No. An open door doesn't move air fast enough, and CO migrates from the garage into the living space and stays there. This exact setup is behind a large share of generator deaths. Outside, at least 20 feet away, is the only safe placement.
Do inverter generators produce carbon monoxide?Yes. They're quieter and sip fuel, but the engine still burns gasoline and the exhaust still carries CO. Some newer models add a sensor that shuts the unit down if CO builds up nearby — treat that as a last-resort backup, never as permission to move it closer to the house.
How long can a portable generator run continuously?It has to stop for refueling, and most manufacturers want the oil checked regularly — read your manual for the interval. Runtime on a tank is commonly in the 8–12 hour range at half load. The refueling stop is a feature, not an inconvenience: it forces the cool-down that makes filling the tank safe.
What if my CO alarm goes off while the generator is running?Get everyone — including pets — outside and call 911 from there. Don't open windows, don't shut the generator off first, don't go back for belongings. Wait for the fire department to clear the house. CO leaves no smell to tell you the air is safe again; their meters do that.
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UHUsefulHow Editorial TeamWe test home repairs in real houses and write the guides we wish we'd had. Every guide is reviewed against manufacturer instructions and current building codes.