How Far Should a Generator Be From the House?

The power went out two hours ago and the freezer is warming up. You pull the portable generator out of the shed, set it on the driveway about eight feet from the back door, and run a cord through a cracked window. By midnight the house smells normal, everyone is asleep, and carbon monoxide is quietly entering through that cracked window, the dryer vent, and a gap under the garage door. This scenario is not rare: portable generators are one of the leading sources of fatal CO poisoning in the United States, and "too close to the house" is the common thread. This page covers the recommended safe distance, a practical placement checklist, and the most common mistakes that still cause tragedies.

In 60 Seconds

• Run portable generators outdoors only, never inside a home, garage, basement, shed, or crawlspace.
• Place the generator at least 20 feet (about 6 meters) from doors, windows, and vents, farther if wind or terrain funnels exhaust toward the building.
• Point the exhaust away from the house and neighboring homes.
• "20 feet away" can still be dangerous if the generator sits in a courtyard, under a deck, or near an HVAC intake.
• Ensure CO alarms are working and have fresh sensors, especially during outages when generator use peaks.

Why Distance Matters

Generators produce carbon monoxide in their exhaust. CO is invisible and odorless, so you cannot rely on smell to tell whether fumes are entering your home. Even small exhaust infiltration can build up indoors, especially overnight when doors and windows are closed. The goal of distance rules is to keep exhaust dilution high and prevent the plume from re-entering the structure through openings or HVAC intakes.

The "20-Feet Rule", and Why It Is a Minimum

A widely cited safety baseline is at least 20 feet from doors, windows, and vents. This distance comes from CPSC guidance and is meant to reduce the chance of exhaust drifting back into the home. However, distance alone is not the whole story. "20 feet away" can still be dangerous if:

• The generator is aimed toward an open window.
• It sits in a courtyard or between buildings that trap fumes.
• It is placed below a window well or near a basement entry where air can pool.
• Wind pushes the exhaust plume directly toward the house.

Treat 20 feet as the starting point, not the finish line. Adjust based on your specific layout.

The same 20 feet is doing a second job that CO-focused guidance rarely mentions. FEMA sets the distance against fire as well as against exhaust, and puts the fuel inside it: ready.gov tells households that "generators and fuel should always be used outdoors and at least 20 feet away from windows, doors and attached garages", and separately to let the generator cool before refuelling, because fuel spilled on hot engine parts can ignite. A running generator is a hot engine with a fuel can beside it. That is worth knowing because it rules out a placement people otherwise like, which is tucking the unit against the house wall out of the rain.

Outdoors Is Not the Same as Safe

The uncomfortable number behind this page comes from CPSC's own records. Of the 1,332 deaths involving portable generators between 2004 and 2021, 79, about 6 percent, happened with the generator operating outdoors the whole time. Those are not garage cases or basement cases. Those are people who followed the headline instruction and still died, which is what distance and aim exist to prevent.

There is a second finding that matters for anyone who bought a generator with automatic CO shutoff. The Commission states that outdoors, weather, exhaust direction and other conditions can hold CO around the machine below the level that trips the sensor while the exhaust still reaches the house. In its words, a G300-compliant generator "(that is not compliant with UL 2201) running outdoors that does not shut off presents the same risk of CO poisoning as a noncompliant generator". That parenthetical is doing the work, and CPSC gives its reason in the same footnote: G300 sets no limit on how much CO the engine may emit and UL 2201 does, so a machine built to both standards is outside the finding. Check which one yours meets before you rely on it. CPSC cites a three-fatality incident involving exactly the gap: a G300 generator, used outside, near a home.

Read that alongside the placement rules below. The safety feature is at its weakest in the setting where you are most likely to rely on it, so outdoors the distance and the direction of the exhaust are the protection, not the sensor. For how the same standards behave in a garage, see running a generator in a garage with the door open.

Which Standard Yours Meets, and How to Tell

That check is worth two minutes because the answer is printed on the machine and almost nobody looks. The marketing name does not tell you: CO Shield, CO Guard and CO Detect all mean a shutoff exists, and none of them names the standard it was tested to. What you want is the standard number itself, either ANSI/PGMA G300 or UL 2201, and it appears on the nameplate near the control panel and on the carton rather than in the product listing. For UL 2201, UL's own advice to buyers is to look for its holographic label and Enhanced Mark. G300 requires markings of its own in a readily visible place, covering the shutoff system's warnings and the hazard of tampering with it.

If the only thing you can find is a brand name and no standard number, you cannot assume the stricter one. The two are not interchangeable: they trip at different concentrations, measure at different distances from the machine, and only one of them limits how much CO the engine may emit in the first place. The comparison, with CPSC's modelling of what each would have prevented across 1,332 deaths, is set out on our generator in a garage page.

Buying advice, in one line, because the finding above constrains it: buy the shutoff, prefer UL 2201, and then place the machine as though it had neither.

When You Do Not Have 20 Feet

Every result on this query, and everything above on this page, assumes a lot with 20 feet of open ground in it. Terraced houses, zero-lot-line suburbs, apartment balconies, basement flats and enclosed rear courtyards are exactly the places where the "almost outside" placements above get chosen, and telling that reader only what not to do leaves them holding a generator with nowhere to put it.

Work through it in this order. Measure the real distance to every opening rather than to the wall, because the number that matters is to the nearest window, door, dryer vent, soffit or air intake, and in a narrow lot the nearest opening is often on the neighbor's building. Then look for the direction that buys you the most: an unobstructed front garden or street frontage usually beats a sheltered rear courtyard, even though the courtyard feels safer, because a courtyard with walls on three sides holds exhaust the way a garage does. Add a CO alarm in the room closest to wherever the machine ends up, and keep the windows on that side shut for as long as it runs.

Then the part no page in this SERP will say: for some layouts the honest answer is that a portable generator cannot be run there safely at all. A basement flat with a lightwell, an interior courtyard enclosed on four sides, and a balcony over an occupied room are all cases where there is no placement that satisfies the rule, and buying a bigger extension cord does not create one. If that is your building, the useful spend is a battery power station, which produces no combustion products and can run indoors, or an arrangement with somebody whose lot has the distance yours does not.

Placement Checklist

Common "Almost Outside" Mistakes That Still Cause CO Poisoning

Many CO incidents happen when the generator is "basically outside" but still in a partially enclosed or airflow-trapping area. These setups can funnel exhaust straight into living spaces:

• In a garage with the door open, still dangerous. See can you run a generator in a garage with the door open.
• On a covered porch or screened-in patio, roof and walls trap exhaust.
• Under a deck, especially near a basement door or dryer vent outlet.
• Next to a window A/C unit or near a fresh-air HVAC intake.
• In an enclosed courtyard between buildings where air recirculates.

How to Verify Your Placement Is Safer

• Stand where people sleep and look for direct airflow paths from the generator location to bedroom windows and vents.
• Check wind direction periodically, storms can shift wind and push exhaust toward the house.
• If you use a portable CO monitor, place it near sleeping areas as an extra layer (not a replacement for installed alarms).
• Ensure working CO alarms are installed on every level and not expired.

No State Law Sets a Generator Distance. One Sets a Duty.

The 20 feet is guidance, and it is worth knowing how completely it is guidance. We hold carbon monoxide law for all 51 US jurisdictions, and searched every record for a generator setback under six spellings. Not one jurisdiction sets a distance. A generator is named at all in only seven of the 51 records, and where it is named the subject is alarms rather than metres: Alaska on properties running on generator supply for part of the year, Oregon on the generator room as an equipment-room trigger, New York City on what a detector may switch off. So if an inspector ever measures your generator's position, they are working from the manufacturer's manual or the utility's rules, not from a carbon monoxide statute, and nobody is going to fine you for nineteen feet.

Louisiana is the single exception, and it does something better than measuring. Under R.S. 40:1581 a professional installing a generator in a one- or two-family dwelling has to include at least one operable carbon monoxide detector with a long-life sealed battery as part of the job. It is the only provision in the fifty-one that attaches a carbon monoxide duty to the generator rather than to the building, and it puts the alarm in the house at the one moment somebody qualified is already standing in it. If you are having a standby unit fitted anywhere else, that is a line worth adding to the quote yourself.

New York City is the other record that decided something about generators, and it decided to leave them alone. Its Building Code Section 915.3.1 makes a carbon monoxide detector at the source shut that source down automatically, and then excepts generators from the rule. The logic is hard to argue with during an outage: a detector that kills your generator kills the power to everything else, the sump pump and the medical equipment included. It also means the one machine most likely to be producing carbon monoxide is the one machine the interlock will not stop, which is the reason distance and alarms carry the whole load here.

Transfer Switches: Reduce CO Risk by Design

The safest "distance" is achieved when you do not need to drag cords toward the house. For homes with frequent outages, a licensed electrician can install a transfer switch or interlock that lets you keep the generator in a consistent safe spot and connect power correctly. This also eliminates the common temptation to run a generator closer because the extension cords do not reach.

A transfer switch also prevents backfeeding, sending power back into utility lines, which is a separate electrical hazard. If a full transfer switch is not practical, a manual interlock on the main panel is a simpler alternative that still lets you place the generator at a safe distance and route power through the panel instead of through extension cords snaked through windows.

CO Alarms During Outages

Placement is only half the protection, and the other half has a scheduling problem: a hardwired alarm with no battery backup is offline for the whole outage. Do this before storm season rather than during one. Walk the house, press test on every CO alarm, and check the manufacture date on each so anything past its end-of-life date gets replaced while the shops are open. Add a battery unit near the entry closest to wherever the generator usually ends up, since that is the doorway the plume finds first. For coverage planning, see how many CO detectors do I need.

Sources & References

• CPSC: Carbon Monoxide Information Center
• CDC: Carbon Monoxide Poisoning Prevention
• NFPA: Carbon Monoxide Safety
• CPSC, Safety Standard for Portable Generators, supplemental notice of proposed rulemaking, 20 April 2023, for the outdoor fatality share and the shutoff-outdoors finding
• FEMA, Ready.gov, Power Outages, for the 20-foot figure applied to generators and fuel together, and the cool-before-refuelling rule
• US Fire Administration (FEMA), 5 Steps to Portable Generator Safety, for the outdoors-and-away-from-openings rule; note that this handout states no distance

Published: January 15, 2024