Generators, Carbon Monoxide, and Pets: The Rules That Keep Them Alive

Run a portable generator outdoors only, at least 20 feet from the house with the exhaust pointed away from windows, doors, and vents. Never run one in a home, garage, basement, crawlspace, shed, or porch, even with doors open, and put carbon monoxide (CO) alarms on every level of the home. Generators are the most common source of CO during power outages, and pets cannot smell the gas, read an alarm, or leave on their own. This page covers what the U.S. Consumer Product Safety Commission (CPSC), the American Red Cross, and veterinary sources (the ASPCA, ASPCApro, Merck Veterinary Manual, and VCA Animal Hospitals) publish on generator placement, CO alarms, and CO poisoning in pets.

If your pet shows vomiting, weakness, stumbling, seizures, collapse, or unusually red or cherry-colored gums after any generator use or power outage, move it to fresh air immediately and get to an emergency vet now. CO poisoning is an emergency for a veterinarian, not something to wait out at home. Your vet’s word beats this page at every step.

The Rule: Generators Never Run Indoors

This is not a caution. It is an absolute. CPSC’s list is a home, garage, basement, crawlspace, shed, or porch, even if doors and windows are open. The CDC says the same for a home or garage. The Red Cross draws the line at any partially enclosed area. Opening a door does not prevent dangerous CO buildup; it only changes how long it takes to reach a dangerous level.

The same goes for any fuel-burning device (grills, camp stoves, charcoal), per the Red Cross. If it burns gas, propane, or charcoal, it stays fully outdoors.

The 20-Foot Rule for Portable Generators

Run a portable generator outdoors only, at least 20 feet from the house, with the exhaust pointed away from windows, doors, and vents, per CPSC’s generator safety guidance. This distance protects everyone inside, people and pets both, because CO migrates indoors through any opening, gap, or vent, not just an open door.

CPSC restated the 20-foot rule in its hurricane-season release of May 27, 2026: operate generators outdoors only, at least 20 feet from homes and buildings, with exhaust directed away from windows, doors and vents.

Two federal agencies, two reference points. CPSC measures the 20 feet from the house. The CDC tells consumers to run a generator outside, more than 20 feet away from any windows, doors, and vents. On a house with a window on the wall nearest the generator, those are not the same spot. Measure to the nearest opening, not the nearest wall, and you satisfy both. Treat 20 feet as a floor: point the exhaust away from the house on top of that distance, since wind can carry CO back toward a building even from 20 feet out.

Stationary (standby) generators: no rule at all

Many generator-safety pages get this wrong, so check the status before you assume a permanently installed generator is the safe option.

In June 2025, CPSC staff published a report on the CO hazard from stationary generators. Its findings: the 5-foot enclosure-to-opening clearance allowed in NFPA 37 is inadequate to prevent dangerous concentrations of CO from getting inside, past attempts to have CO requirements adopted into NFPA 37 have been unsuccessful, and there are no codes or standards that address the CO poisoning hazard associated with stationary generators. Staff recommended that the NFPA 37 technical committee raise the separation distance between the generator and openings into structures from the current 5 feet to at least 25 feet, and made parallel recommendations to the UL 2200 committee.

The evidence came from Hurricane Ida. After the 2021 outages around New Orleans, CPSC received information on 256 homes reporting at least one CO exposure incident, and staff investigations identified the home’s stationary generator as the source in 105 of them. In those incidents the exhaust traveled at least 25 feet from the enclosure, spread laterally by at least 6 feet, and rose more than 10 feet, and higher where an obstruction deflected it upward, at concentrations high enough to set off the homes’ CO alarms.

Mind the report’s status. It is a staff document, prepared by CPSC staff and not reviewed or approved by the Commission; every page is stamped that it has not been reviewed or accepted by the Commission. It is not an agency rule and not code. It is the best published evidence on this hazard, and it says the clearance your installer worked to is a fire clearance that was never designed to stop carbon monoxide.

For a household with animals: if you have or are quoting a standby generator, raise placement with your installer as a CO question, and put the generator as far from doors, windows and intake vents as the site allows, not at the minimum the code permits. A crated dog in a back room cannot leave.

Never place a generator, portable or stationary, near an intake vent, window, or door, even at the recommended distance.

Why Fans and Cracked Windows Don’t Work

A running generator produces CO fast enough that partial ventilation is not a meaningful safeguard. The CPSC, CDC, and Red Cross agree: opening a window, running a fan, or leaving a garage door up does not make indoor or near-indoor generator use safe. The only safe placement is fully outdoors, at the CPSC’s distance, with exhaust directed away from the building. This is the most common mistake during an outage, so guard against it hardest.

CO Alarms: Where They Go, and Why Pets Raise the Stakes

Install battery-powered or battery-backup CO alarms on every level of the home and outside every separate sleeping area, per the CPSC and American Red Cross. The CDC’s own instruction is narrower: battery-operated or battery-backup CO detectors near every sleeping area. Take the every-level part from CPSC and the Red Cross. The CDC adds two maintenance rules worth a reminder: check the detector batteries when you change the clocks each spring and fall, and “Replace your CO detector following the manufacturer’s instructions or every 5 years.” Test alarms monthly.

In a pet household, interconnection matters most. CPSC’s 2026 guidance states that interconnected alarms are best, because when one sounds, they all sound. A cat shut in a basement laundry room during an outage is not helped by an alarm sounding two floors up in a room nobody is in. Interconnection turns one alarm near the source into a signal that reaches the person who can go get the animal.

This is not optional in a household that shelters pets. A CO alarm is the only realistic early warning your animals have, because they cannot smell the gas, read the alarm, or wake you the way a person might notice a headache. If your pets spend time in a space without people nearby (a laundry room, a garage-adjacent mudroom, a finished basement), make sure alarm coverage reaches there too.

The one spec to check when buying a generator

CPSC recommends asking retailers for a portable generator with a safety feature that shuts the unit off automatically when high CO concentrations are present. In its 2026 hurricane release it names the certifications that carry it: models certified to PGMA G300-2023 and UL 2201-2023 include CO safety technologies designed to significantly reduce CO poisoning risk, and CPSC notes that UL 2201 certified models have reduced CO emissions in addition to the shut-off feature.

That is a checkable spec: a named standard with a year on it can be found on the unit or confirmed by a retailer, unlike a box that just says “CO sensor.” It does not replace the 20-foot outdoor placement rule. It is the layer that catches the night someone gets the placement wrong.

Why “Pets Get It First” Isn’t the Right Framing

A common claim on pet-safety blogs is that dogs and cats are poisoned by CO faster than people because they are smaller, breathe faster, or sit closer to the floor: a “canary in a coal mine” argument. None of the sources this page relies on makes that claim. The ASPCA’s carbon monoxide guidance says the opposite of the floor-proximity piece: CO is roughly the same density as room air, so animals close to the ground are at no more risk than taller animals in the same space. The Merck Veterinary Manual’s description of CO as slightly lighter than air points the same way. This is not a gas that settles at dog height.

One claim in this territory is sourced:

• Birds are more vulnerable to CO. Per the ASPCA, birds, because of their unique respiratory system, are more sensitive to the effects of carbon monoxide than other animals are. ASPCApro, the ASPCA’s professional channel for veterinarians, says under its “Species Sensitivity” heading that birds show symptoms at 900 ppm carbon monoxide, and that mice show no clinical signs until almost double that amount. That is a comparative figure written for veterinarians, not a level to design anything around: a household CO event is dangerous to every animal in it long before anyone measures parts per million. It applies to birds, not to dogs and cats generally. If your household includes a parrot or other bird, our bird and parrot emergency preparedness guide covers the wider fume-sensitivity problem, of which generator exhaust is one case.

The real reason pets are at extra risk in a CO event has nothing to do with body size. They cannot self-evacuate when an alarm sounds, cannot interpret the alarm as a signal to act, and cannot tell you they feel dizzy or short of breath.

Signs of CO Poisoning in Pets: When to Stop and Go to the Vet

CO is colorless and odorless. Pets cannot smell it, cannot sense it coming, and cannot warn you, per Pet Poison Helpline. Alarms are the only reliable detection method. Prevention beats recognizing symptoms after the fact, but symptoms matter too.

Clinical signs of CO poisoning in pets, per the ASPCA, ASPCApro, and VCA Animal Hospitals:

Severity	Signs
Mild to moderate	Depression, vomiting, weakness
Severe	Coma, seizures, labored breathing (dyspnea), cardiac arrhythmias, acute lung injury, death
Dog-specific	Cherry-red or unusually red gums and mucous membranes, per VCA Animal Hospitals
Possible lasting effects	Permanent deafness and blindness are also possible, per the ASPCA

Any of these signs after generator use or a power outage means get the pet to fresh air immediately and call a veterinarian or the ASPCA Animal Poison Control Center. Do not wait to see if it resolves, and do not attempt any home treatment. Per ASPCApro, veterinarians treat CO poisoning with oxygen therapy. There is no home version of it.

If you end up at the vet: VCA Animal Hospitals notes that pulse oximetry, a common quick oxygen-saturation check, can be unreliable and overestimate oxygen levels in CO-exposed animals. The Merck Veterinary Manual says most pulse oximeters do not detect carboxyhemoglobin, and that pulse CO-oximetry is required. Merck also notes that blood carboxyhemoglobin levels correlate poorly with how severe the poisoning is. Don’t be surprised if your vet runs additional tests, and don’t read a normal-looking pulse-ox number as an all-clear.

Delayed effects are real. ASPCA and ASPCApro both note that neurologic complications can appear 3 to 6 days after apparent recovery. A pet that seems fine hours after a suspected exposure is not necessarily in the clear. Mention the exposure to your vet even if symptoms have resolved, and watch for new signs over the following several days.

If You Suspect Poisoning

Two poison-control lines are available if you suspect CO exposure or any other poisoning:

• ASPCA Animal Poison Control Center: (888) 426-4435, available 24 hours a day, 365 days a year. A consultation fee may apply.
• Pet Poison Helpline: (855) 764-7661, available 24/7. A per-incident fee applies, and follow-up consultations are included.

For a pet showing active severe symptoms (seizures, collapse, labored breathing), go directly to the nearest emergency vet rather than calling a poison-control line first; call on the way if you can.

Keep the Generator Outside, Every Time

Keep every portable generator fully outdoors, at least 20 feet from the house, with exhaust pointed away from windows and doors. No exceptions for open windows or running fans. For a stationary (standby) generator, NFPA 37’s 5-foot enclosure-to-opening clearance is a fire clearance, never designed to address carbon monoxide, and CPSC staff have recommended, in a report the Commission has not reviewed or approved, that the technical committee raise that separation to at least 25 feet, measured from openings into the structure. Raise that figure with your installer as a carbon monoxide question. Put CO alarms on every level of the home and outside every sleeping area, and test them monthly. Your pets rely on that alarm and that distance. If a pet ever shows symptoms after generator use or an outage, get to a vet now.

For the rest of what a power outage means for your household (refrigerated medication, aquarium and reptile life support, portable power options), see the pets and power outages hub. If you are weighing a portable power station instead of or alongside a generator, our portable power station guide covers what is rated for pet-related loads, and our head-to-head on a quiet inverter generator versus a battery power station weighs this carbon monoxide problem against runtime and the noise a frightened animal has to sit through. Outages tied to hurricanes or winter storms have their own planning needs: see hurricane pet preparedness and winter storm pet prep.