Carbon Monoxide Safety: Generators, Heaters and CO Alarms

By GoldBlock WorkshopPublished Updated

The short answer

Carbon monoxide (CO) is “an odorless, colorless gas that kills without warning” (CDC), produced when fuel burns, and the CDC notes that people who are asleep can die from it before they have symptoms. The CDC and CPSC rules: keep generators, grills and other fuel-burning devices out of the home and garage, running generators more than 20 feet from the home with the exhaust pointed away, and never heating a home with a gas oven (the full CDC and CPSC generator wording is in the generator section below). CPSC: “Install battery-operated alarms or alarms with battery backup on each level of the home and outside separate sleeping areas,” tested monthly. If an alarm sounds or someone feels sick, CPSC: “Get outside immediately, and call 911 from a fresh-air location.”

Key numbers

  • 400+Americans die each year from unintentional CO poisoning not linked to firesSource: CDC
  • 100,000+emergency department visits a year for the same cause, and more than 14,000 hospital staysSource: CDC
  • 20 feetminimum distance from the home and from windows, doors and vents for a running generator: CDC says more than 20 feet, CPSC at least 20 feet with exhaust facing awaySource: CDC; CPSC
  • Monthlyhow often to test CO alarmsSource: CPSC

What is carbon monoxide, and why is it so dangerous?

Carbon monoxide is a gas produced whenever fuel burns, and it is dangerous because you get no warning: the CDC calls it “an odorless, colorless gas that kills without warning.” It poisons people and animals who breathe it.

Inside the body, CO binds to the blood and forms carboxyhemoglobin, which cuts the blood’s ability to carry oxygen (EPA). Confusion and sleepiness are among the listed symptoms (CPSC).

  • Everyone is at risk, the CDC says. Infants, older adults, and people with chronic heart disease, anemia or breathing problems are more likely to get sick.
  • Sleep and alcohol remove the warning. The CDC notes that people who are sleeping, drunk or under the influence can die from CO poisoning before they have symptoms.

Where does carbon monoxide come from at home?

From anything that burns fuel: the CDC names gas- and oil-burning furnaces, portable generators and charcoal grills, and the EPA adds unvented kerosene and gas space heaters, leaking chimneys, back-drafting fireplaces and wood stoves, gas stoves, and car exhaust from attached garages.

CPSC’s 2022 estimates (May 27, 2026): generators accounted “for 41 percent of all non-fire CO deaths related to consumer products under CPSC’s jurisdiction” from 2012 to 2022, and “An estimated 76 deaths (28%) were associated with some type of heating appliance” in 2022.

Source The rule Official source
Portable generator Outdoors only, at least 20 feet from the house, exhaust directed away, never in any enclosed space; the full CDC and CPSC wording is in the next section. CDC; CPSC
Car or truck Never run it inside a garage attached to a house, even with the garage door open. CDC
Charcoal grill Never burn charcoal indoors. CDC
Gas oven or stove Never heat your house with a gas oven. CDC
Furnace, water heater, other gas, oil or coal appliances Have them serviced by a qualified technician every year. CDC; CPSC
Fuel-burning space heater, fireplace, wood stove The EPA lists unvented kerosene and gas space heaters, leaking chimneys and back-drafting fireplaces and wood stoves as indoor CO sources. The CDC says to use combustion heaters only if “properly vented to the outside”; heater choices and fire rules are in Home Temperature During Outages. EPA; CDC

Sources for the table: CDC: Carbon Monoxide Poisoning Basics, CDC: Generator safety fact sheet (PDF), CPSC: Carbon Monoxide Information Center, EPA: Carbon Monoxide’s Impact on Indoor Air Quality.

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

Outdoors only, at least 20 feet from the house, with the exhaust directed away, and never in any enclosed or partly enclosed space. The two agencies’ words, which this page uses throughout:

  • CDC: “Never use a generator inside your home or garage, even if doors and windows are open.” “Only use generators outside, more than 20 feet away from your home, doors, and windows,” and “more than 20 feet away from any windows, doors, and vents.”
  • CPSC: “NEVER operate a portable generator inside a home, garage, basement, crawlspace, shed or other enclosed spaces.” “Opening doors or windows will not provide enough ventilation to prevent the buildup of lethal levels of CO.” “Operate portable generators outside only, at least 20 feet away from the house.” “Don’t operate a generator on a porch or in a carport.” “Direct the generator’s exhaust away from your home and other buildings’ entrances.” “Close windows and seal off vent openings that are near the generator or in the path of its exhaust.”
  • Why the rule is “never inside”: CPSC’s review of generator deaths from 2012 to 2022 found that at fixed homes, 73% happened with the generator inside the home (including the living space, a basement or crawlspace) and another 18% with it in an attached garage, enclosed carport or attached barn.
  • Other buildings count. CPSC’s rule points the exhaust away from “your home and other buildings’ entrances,” not only your own.

Sizing a generator, connecting it to house wiring through a transfer switch (Virginia Cooperative Extension, OSHA and CPSC quoted there) and the other backup power choices are covered in Backup Power for Vital Loads.

Where should carbon monoxide alarms go?

On every level of the home and outside each sleeping area, as battery-powered or battery-backup alarms. CPSC: “Install battery-operated alarms or alarms with battery backup on each level of the home and outside separate sleeping areas.” The U.S. Fire Administration says “in a central location outside each separate sleeping area and on every level.”

  • UL 2034. CPSC and the EPA point to alarms that meet the UL 2034 safety standard.
  • Interconnected alarms. CPSC: “Interconnected CO alarms are best; when one sounds, they all sound.”
  • An alarm is a backup, not a fix. The EPA says a CO detector is “NOT A REPLACEMENT” for proper installation, use and maintenance of fuel-burning appliances.

CO alarms and smoke alarms are separate devices; CPSC’s instruction covers both: “Test CO and smoke alarms monthly to make sure they are working properly and replace batteries if needed.”

How do I test and maintain CO alarms?

Test every alarm once a month, replace batteries as the maker says, and replace the alarm itself when its instructions say or when the end-of-life signal sounds (CPSC).

What should I do if a CO alarm goes off?

The steps are in the notice at the top of this page: outside first, then 911 from a fresh-air location, or the fire department if 911 is not available (CPSC), and “Never ignore an alarm when it sounds” (CPSC).

  • Symptoms. The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as “flu-like.” CPSC: “If you start to feel sick, dizzy, or weak while using a generator, get to fresh air RIGHT AWAY.”

What CO alarms and good habits can and cannot do

The EPA says a CO detector is “NOT A REPLACEMENT” for proper installation, use and maintenance of fuel-burning appliances, and the CDC says to have heating systems and gas appliances serviced by a qualified technician every year. An alarm does not change the placement rules above: CPSC’s words are that opening doors or windows “will not provide enough ventilation to prevent the buildup of lethal levels of CO.”

Common misunderstandings about carbon monoxide

Each belief below is answered from the CDC or CPSC.

  • “I’d smell it.” You cannot; the CDC calls CO “an odorless, colorless gas that kills without warning.”
  • “The garage door is open, so it’s fine.” The CDC says never run a vehicle in an attached garage even with the door open, and the generator rule above says the same for generators.
  • “It’s only a few minutes.” Neither agency gives a safe time for running a generator or grill indoors; both say never, and the CDC warns that sleeping people can die before they have symptoms.
  • “I feel like I have the flu.” The CDC describes CO symptoms as flu-like; CPSC: “If you start to feel sick, dizzy, or weak while using a generator, get to fresh air RIGHT AWAY.”
  • “A smoke alarm will catch it.” CPSC treats CO alarms and smoke alarms as separate devices: “Test CO and smoke alarms monthly.”

Common questions

Can I run my car in an attached garage with the garage door open?

No. The CDC says never run a car or truck inside a garage attached to a house, even with the garage door open.

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

No. CPSC: “NEVER operate a portable generator inside a home, garage, basement, crawlspace, shed or other enclosed spaces,” and opening doors or windows “will not provide enough ventilation.” Outside only, at least 20 feet from the house, exhaust directed away (CPSC); the full wording is in the generator section above.

Is it safe to heat my house with a gas oven?

No. The CDC says never heat your house with a gas oven.

Who is most at risk from carbon monoxide?

Everyone is at risk (CDC). Infants, older adults, and people with chronic heart disease, anemia or breathing problems are more likely to get sick.

Does a CO alarm mean I can skip the yearly furnace check?

No. The EPA says a CO detector is not a replacement for proper installation, use and maintenance of fuel-burning appliances, and the CDC says to have heating systems and gas appliances serviced by a qualified technician every year.

What are the symptoms of carbon monoxide poisoning?

Headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as flu-like (CDC). People who are asleep or intoxicated can die before they notice symptoms.

Where to go next

Sources