Portable Generator Safety: Carbon Monoxide, Backfeeding, and How Far From the House

Key points

• Portable generator safety comes down to one gas you can't smell. CPSC puts the toll at roughly 100 deaths a year from generator carbon monoxide.

• Run it outside only, at least 20 feet from the house, exhaust pointed away from windows, doors and vents. Never a garage, never a carport, never a porch, never a basement or crawlspace.

• Battery-powered CO alarms (or CO alarms with battery backup) on every level and outside every sleeping area. Test them monthly.

• Never plug a generator into a wall outlet. That's backfeeding, and it can electrocute a utility line worker. Use a transfer switch or an interlock kit installed by an electrician.

• Look for a generator certified to ANSI/PGMA G300 or UL 2201. Both shut the engine off when carbon monoxide builds up.

Portable generator safety isn't really about the generator. It's about a colorless, odorless gas the engine makes, and about 20 feet of distance most people don't leave. The U.S. Consumer Product Safety Commission says an average of about 100 people die in the U.S. each year from carbon monoxide poisoning caused by portable generators.

Almost none of those deaths involve a broken generator. They involve a working generator in the wrong place. That's good news, because placement is something you control completely, for free, in about 90 seconds. Here's how to get it right.

Why is portable generator safety mostly a carbon monoxide problem?

Because a small gasoline engine puts out carbon monoxide faster than almost anything else you own, and you cannot detect it with your senses. Carbon monoxide (CO) has no color, no smell and no taste. The CDC reports that more than 400 Americans die every year from unintentional CO poisoning not linked to fires, more than 100,000 go to an emergency department, and more than 14,000 are hospitalized.

Generators are the single biggest consumer-product source of it. A CPSC report covering 2009 through 2019 tied portable generators alone to an estimated 765 non-fire CO poisoning deaths, about 40 percent of all CO deaths related to consumer products. An earlier CPSC review of 1999 to 2012 found 74 percent of generator deaths happened at fixed-structure homes, many with the generator running inside the home's living space.

That is the whole article in one line. The deaths are not scattered freak accidents. They cluster in one pattern: the generator was indoors, in an attached garage, or outdoors but parked too close to an open window or door.

The symptoms are the second half of the trap. CDC lists them as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, and notes they're often flu-like. During a multi-day outage, when nobody has slept well, "I have a headache and I feel sick" is exactly what you'd expect to feel anyway. That's why the alarm matters more than your judgment does.

How far from the house does a generator need to be?

At least 20 feet, outside only, with the exhaust pointed away from the building. CPSC's guidance is to operate a portable generator at least 20 feet from homes and buildings, with exhaust directed away from windows, doors and vents. CDC says the same and adds the openings explicitly: never run it less than 20 feet from any window, door or vent.

The full placement rule, in plain terms:

• 20 feet minimum from the house, measured to the nearest wall, not to the nearest door you happen to be using.

• Exhaust pointed away from the structure. Turning the unit 180 degrees costs nothing and moves the plume.

• Never inside a garage, attached or detached, with the door open or closed.

• Never under a carport, on a covered patio, or on a porch. CPSC calls out the porch and carport specifically: convenient, but too close to the home.

• Never in a basement, crawlspace, shed or any other enclosed or partly enclosed space.

• 20 feet of clearance from every opening, including dryer vents, soffit vents, window air conditioners and the gap under a door. Those are all paths into the house.

• Not in standing water or heavy rain. The U.S. Fire Administration warns that using a generator in a wet area can cause shock or electrocution. Put it on dry ground or a raised pad, under an open-sided canopy that does not trap exhaust.

The part most guides skip: 20 feet is a floor, not a target. Wind matters. If the wind is pushing from the generator toward the house, move it farther or move it around the corner. And 20 feet from your house may be 8 feet from your neighbor's bedroom window. In a dense neighborhood that is their exposure, not just yours, which is worth a conversation before the storm and fits naturally into a plan you have already worked out with the people on your street.

Why is a running generator in an attached garage dangerous even with the door open?

Because an open garage door does not make a garage outdoors. It makes it a partly enclosed box with one wall missing, and carbon monoxide still pools in it and then migrates into the house through the connecting door, the attic access and every gap in the shared wall.

CDC is blunt: never use a generator inside your home or garage, even if doors and windows are open. FEMA adds the other half of the myth, that a fan will fix it: "Using fans will not prevent carbon monoxide build-up in the home."

NIOSH has flagged this exact belief. Its alert on small gasoline engines notes that CO "can accumulate rapidly in enclosed or semi-enclosed spaces" and that people wrongly assume they can avoid risk by opening doors and windows or by running exhaust fans. The same document describes five workers treated for CO poisoning after running two 8-horsepower gasoline pressure washers in a poorly ventilated underground parking garage. Not a generator, same engine, same gas, same outcome.

An attached garage is the worst version because it shares air with your house. Warm air rises through the house and pulls replacement air in from wherever it can get it, and the garage is one of those places. You can be asleep two floors up and still be breathing garage air.

Where should carbon monoxide alarms go, and what kind do you need?

Battery-powered CO alarms, or CO alarms with battery backup, on every level of the home and outside each separate sleeping area. CPSC's wording is "battery-operated CO alarms or CO alarms with battery backup on each level and outside separate sleeping areas," with interconnected alarms preferred so that when one sounds, they all sound.

Battery backup is the non-negotiable part, and the reason is almost funny if it weren't so grim. The exact moment you need a CO alarm most is the moment your power is out. A plug-in-only alarm is dead weight during an outage. Check yours today. If it only has a plug and no battery, it isn't protecting you when it counts.

• One outside each sleeping area, in the hallway, where the sound will actually wake somebody.

• One on every level, including the basement.

• Not right next to a fuel-burning appliance and not in a dead-air corner. Follow the alarm's own instructions for mounting height.

• Test monthly. CPSC says to test alarms monthly to make sure they are working.

• Replace on schedule. CO sensors age out. The date is printed on the back of the unit, and most are good for 7 to 10 years. An expired alarm is a decoration.

If a CO alarm sounds, get everyone outside into fresh air first and call 911 from outside. Do not open windows and go back in to look around. If anyone is unconscious, confused, or will not wake up, that is a 911 call, not a wait-and-see.

What are the CO shutoff generator standards, and what should you look for when buying?

Look for a label saying the unit meets ANSI/PGMA G300 or UL 2201. Both require a sensor that shuts the engine down when carbon monoxide builds up around it. UL 2201 goes further and also limits how much CO the engine makes in the first place.

The numbers behind the labels, from CPSC's rulemaking record in the Federal Register:

• ANSI/PGMA G300 requires the generator to shut off before CO exceeds 400 parts per million on a 10-minute rolling average, or 800 parts per million instantaneous.

• UL 2201 requires shutoff at roughly half those levels, 150 parts per million on a 10-minute rolling average or 400 parts per million instantaneous, and also caps weighted CO emissions at 150 grams per hour. That second part is why UL 2201 units are called reduced-emission generators.

How much does that matter? CPSC ran a simulation against 511 real historical fatalities. A G300-compliant generator would have prevented about 87 percent of them. A UL 2201-compliant generator would have prevented nearly all of them. CPSC's consumer messaging puts the figures at 86 percent and 100 percent respectively.

Shopping notes, honestly stated:

• Look for the standard on the box, the spec sheet or the data plate. Marketing names like "CO Guard," "CO Sense" and "CO Shield" describe the same idea, but the standard is what you verify. Current versions are G300-2023 and UL 2201-2023, cited together in CPSC's hurricane season guidance.

• A certified unit costs somewhat more. It is the cheapest safety upgrade on the whole machine.

• This does not replace placement. A shutoff sensor is a backstop for a mistake, not permission to run the thing in a garage. CPSC's placement guidance is identical for certified and uncertified units.

What is backfeeding, and why is plugging a generator into a wall outlet dangerous?

Backfeeding is running power backward into your house wiring by plugging a generator into a regular outlet, usually with a cord that has male plugs on both ends. It is dangerous because your home's electricity does not stay in your home. It goes back through your panel, up the service drop, into the utility transformer, and back out onto the neighborhood lines at high voltage.

OSHA states the hazard plainly: "Attaching a generator directly to a building electrical system without a properly installed transfer switch can energize wiring systems for great distances. This creates a risk of electrocution for utility workers and others in the area." FEMA says the same in consumer language, warning that hooking a generator directly into your home power supply "could increase the voltage or could cause a surge to the outside power lines and potentially injure or electrocute an unaware utility lineman."

The line crew restoring your power has grounded and tested that circuit because they confirmed it was dead. A backfed generator makes it live again with nobody's knowledge. It endangers your own house too: a backfed circuit bypasses the panel's protection, so it can overload the wiring behind your walls, and when utility power returns while the generator is still feeding the panel, the two sources collide.

The two correct alternatives, both installed by a licensed electrician:

1. A manual transfer switch. A small sub-panel wired beside your main panel with switches for the specific circuits you want to run. You physically flip each circuit from utility power to generator power. It is impossible for both sources to feed the same wire at once.

2. A panel interlock kit. A metal plate on your existing panel that mechanically prevents the main breaker and the generator breaker from being on at the same time. Usually cheaper than a transfer switch, and it gives you access to any circuit in the panel.

Either one gets you a proper inlet box on the outside wall and a single heavy generator cord. FEMA's guidance is to use a qualified electrician to install the appropriate equipment in accordance with local electrical codes, or ask your utility company to install an appropriate power transfer switch. Get a permit. Your utility usually wants to know.

If you have not done that work yet, the safe interim answer is simple: run appliances directly off the generator with outdoor extension cords. It is less convenient and it is completely safe.

What size extension cord do you need for a generator?

An outdoor-rated cord long enough to keep the generator 20 feet away, with wire heavy enough for the load. CDC frames it as an equipment requirement, not an afterthought: "Use an extension cord that is more than 20 feet long to keep the generator at a safe distance." The U.S. Fire Administration says to connect appliances to the generator with heavy-duty extension cords.

Wire gauge is counted backward. A smaller number means thicker wire. 10 gauge is thicker than 12, which is thicker than 14, which is thicker than 16.

Undersized cords overheat for a simple reason. Thin wire has more resistance, resistance turns current into heat, and that heat is spread over less metal. A 100-foot 16-gauge cord running a refrigerator warms along its whole length, softens its own insulation over time, and drops enough voltage that the motor draws even more current to compensate. That loop ends in a melted cord or a burned-out compressor. OSHA is direct: "Do not use underrated cords, replace them with appropriately rated cords that use heavier gauge wires."

• 12 gauge is the practical minimum for a 50-foot generator run. Go to 10 gauge for 100 feet, or for anything drawing more than about 12 amps.

• Outdoor rated only. University of Texas at Austin EHS guidance notes that a "W" in the cord type marking means it is rated for outdoor use, and that indoor cords have different insulation and a lower amperage rating.

• Match the cord to the load, not to whatever is in the drawer. The cord's amp rating has to cover the appliance.

• Do not daisy chain cords. Every connection is a resistance point and a place for water to get in. Buy the one long cord you actually need.

• Uncoil it fully. A coiled cord under load traps its own heat.

• Inspect before every use. Cracked jacket, exposed copper, or a bent or missing ground pin means it is trash, not a repair project.

How do you refuel and store fuel without starting a fire?

Shut the generator off, let it cool, then refuel. Never pour gasoline into a running or hot machine. OSHA's rule is "Before refueling, shut down the generator and allow it to cool." The U.S. Fire Administration explains the failure mode: "Spilling gas on a hot engine can cause a fire." A muffler runs hot enough to ignite gasoline vapor instantly, and vapor is what actually catches, not the liquid.

• Plan refueling around a real stop. Most portable units run 8 to 12 hours on a tank. Shut down, wait 10 to 15 minutes, then fill.

• Use a proper vented fuel can with a spout. Fill on the ground, never on a truck bed liner.

• Wipe up spills before restarting.

• Keep a fire extinguisher near the generator, not in the kitchen.

For storage, OSHA is clear: "Do not store generator fuels in your home. Store fuels away from living areas." FEMA adds not to store fuel near a fuel-burning appliance such as a gas stove or water heater, since a pilot light and gasoline vapor in the same room is the whole ignition sequence.

Fuel stabilizer is the maintenance piece nobody enjoys and everybody needs. Untreated gasoline starts breaking down in about 30 days and can gum a carburetor within a few months. The habit that works: treat every can when you fill it, run the generator under a small load for 20 to 30 minutes every month or two so treated fuel circulates through the carburetor, and rotate stored cans into your vehicle twice a year. A generator that will not start on the first pull of hurricane season is almost always a fuel problem, not an engine problem.

What about grounding and GFCI?

Follow the manufacturer's grounding instructions for your specific unit, and use ground fault circuit interrupter protection anywhere the setup could get wet. OSHA's guidance is to "make sure a generator is properly grounded and the grounding connections are tight," and to consult the manufacturer's instructions for proper grounding methods.

Portable generators are built as either "bonded neutral" or "floating neutral" units, and the manual tells you which, along with whether a grounding rod is required for your use case. This is one of the few places where reading the specific manual beats a general rule, because the answer differs by machine and by whether you are running cords or feeding a transfer switch.

GFCI is the simpler half. OSHA recommends ground fault circuit interrupters "especially where electrical equipment is used in or around wet or damp locations," because a GFCI shuts off power when current strays outside its normal path. Many portable generators now have GFCI-protected outlets built in. If yours does not, a portable GFCI adapter costs about the price of a pizza. Post-storm ground is wet ground, and that is exactly the condition GFCI exists for. If the storm that took your power also put water on the roads, the depth numbers that decide whether a road is drivable matter more in that moment than anything on the generator does. The National Weather Service's basic instruction is that portable generators should only be operated outdoors in a dry and well ventilated area.

When is an inverter generator or a battery power station the better answer?

Often, and more often than the generator aisle suggests. A conventional open-frame generator is the right tool when you need 5,000 watts or more, for days, and you can safely place it 20 feet out. For most of what people actually run during an outage, it is more machine than the job needs.

An inverter generator is the better answer when you want quiet, clean power and modest capacity. Typical units run 1,600 to 4,500 watts, sip fuel by throttling down under light load, weigh a fraction of an open-frame unit, and produce power steady enough for laptops, routers and modern appliance electronics. They still make carbon monoxide. Every placement rule in this article applies to them exactly the same way.

A battery power station is the better answer when your real need is a CPAP, a phone, a router, medical equipment, a few lamps and a fridge run in cycles, or when you live in an apartment or townhouse with no safe 20-foot placement. The National Weather Service's own writeup on home backup power notes that battery systems "can operate entirely indoors, emit no exhaust and little noise," and that unlike generators, there is no maintenance involved. That indoor operation is the point: no CO risk, no fuel storage, no refueling in the dark.

The honest limits of batteries are capacity and recharge. A 1,000 watt-hour unit will not run a well pump or central air, and once it is empty you need sun or grid power to refill it. If you are weighing that trade, work through how to size a power station by watt-hours instead of watts, because watts alone will steer you wrong.

A lot of households land best on both: a battery station indoors for small critical loads and quiet overnight running, and a generator outside for heavy daytime work. That also cuts generator runtime, which cuts fuel use, noise and CO exposure at once.

When to stop and get help

Some of this is a call for a professional, and some of it is a call for 911. Knowing which is which ahead of time is most of the value.

Call 911 immediately if a CO alarm sounds and anyone is confused, unsteady, unusually sleepy, vomiting or unconscious. Get everyone outdoors into fresh air first, then call from outside, and do not go back in for anything. Tell the dispatcher you suspect carbon monoxide, because it changes what responders bring.

Treat it as an emergency even without an alarm if several people in the house get headachy, dizzy or nauseated at the same time, especially if it improves outdoors and returns indoors. CDC notes that infants, older adults and people with chronic heart disease, anemia or breathing problems are more likely to get sick from CO, so they may show symptoms first. If you are unsure whether an exposure is dangerous, Poison Control at 1-800-222-1222 is free, staffed 24 hours a day, and used to exactly this question.

Call a licensed electrician for anything that touches your panel: a transfer switch, an interlock kit, a generator inlet box, or any question about grounding for a permanent installation. This is not a place for a video and a weekend.

Stop and reassess if the only spot you can find for the generator is a garage, a carport, a porch, a balcony or a patch right beside a window. That is not a placement problem a fan or an open door can solve. It is a signal that a battery power station is the right tool for your home, and that is a completely legitimate answer.

None of this is complicated. It's 20 feet, an alarm with a battery, a cord thick enough for the job, and never plugging into a wall outlet. Get those four right and you've handled the parts that actually kill people. It fits neatly alongside the rest of a 72-hour plan you build before the storm is named.

Frequently asked questions

How far from the house should a portable generator be?

At least 20 feet, outdoors only, with the exhaust pointed away from the building. CPSC specifies at least 20 feet from homes and buildings with exhaust directed away from windows, doors and vents, and CDC adds that it should never run less than 20 feet from any window, door or vent. Wind direction matters, so move it farther if the breeze pushes exhaust toward the house.

Can I run a generator in my garage if the door is open?

No. CDC states directly that you should never use a generator inside your home or garage even if doors and windows are open. An open door does not make a garage outdoors, carbon monoxide still pools there, and it migrates into the house through the connecting door and shared walls. FEMA also notes that running fans will not prevent carbon monoxide build-up.

What is backfeeding a generator?

Backfeeding is plugging a generator into a household outlet so power flows backward into your house wiring. It sends electricity back through your panel and out onto the utility lines, where OSHA warns it can energize wiring systems for great distances and create a risk of electrocution for utility workers. The correct alternatives are a manual transfer switch or a panel interlock kit installed by a licensed electrician.

Do I need a CO alarm if my generator has a CO shutoff sensor?

Yes. A CO shutoff sensor is a backstop for a placement mistake, not a substitute for one. CPSC's placement guidance is the same for certified and uncertified generators, and it still calls for battery-operated CO alarms, or alarms with battery backup, on every level and outside separate sleeping areas. Plug-in-only alarms are useless during the outage when you need them.

What size extension cord should I use with a generator?

An outdoor-rated cord more than 20 feet long, in 12 gauge for shorter runs and 10 gauge for 100-foot runs or heavier loads. Smaller gauge numbers mean thicker wire. OSHA warns against underrated cords and says to replace them with appropriately rated cords using heavier gauge wire, because undersized cords overheat and drop voltage. Do not daisy chain cords together.

Is a battery power station safer than a generator?

For carbon monoxide, yes, because it produces none. The National Weather Service notes that battery systems can operate entirely indoors, emit no exhaust and little noise, and need no maintenance. The trade is capacity and recharge time, so batteries suit CPAPs, phones, routers, lights and cycled refrigerator use rather than well pumps or central air.

You never know, but you can always be ready.

Sources: CPSC, winter storm CO and fire safety tips; CPSC, generator and CO hazards ahead of hurricane season; CPSC, report on CO fatalities; CPSC, portable generators top the CO death report; CPSC, Safety Standard for Portable Generators (Federal Register); CDC, carbon monoxide poisoning basics; CDC, generator safety fact sheet; CDC, protecting yourself during a power outage; NIOSH, CO risk from small gasoline engines; OSHA, Using Portable Generators Safely; FEMA, Use Generators Safely at Home; U.S. Fire Administration, 5 Steps to Portable Generator Safety; NOAA National Weather Service, home power backup; NOAA National Weather Service, carbon monoxide dangers; University of Texas at Austin EHS, extension cords.