Fact-checked by Marcus Hayes, Master Electrician (License #CA-EL-89241), 15 years generator installation experience.
Key Takeaways
Every portable gas and propane generator must be at least 20 feet from any door, window, or vent — regardless of wattage or size.
Generator exhaust must point away from the house and any occupied structure, including neighboring homes.
Standby generators have different clearance rules: typically 18 inches to 5 feet from the house wall, per manufacturer specifications.
Never operate a generator in a garage, basement, shed, porch, or under a deck — even with doors open.
Wind direction matters: if wind blows exhaust toward the house, reposition the generator so exhaust points downwind.
The 20-foot rule for portable generators
A portable generator must be placed at least 20 feet from any door, window, or vent to prevent carbon
monoxide from entering the home. The exhaust must point away from the building. This minimum applies
to all gas and propane generators regardless of size — a 2,200W inverter produces the same lethal CO
as a 12,000W open-frame model.
Never Operate Indoors
Never run a generator in a garage, basement, shed, porch, or under a deck — even with doors and windows
fully open. These spaces trap exhaust and allow carbon monoxide to accumulate to lethal levels within
minutes. Generators must always be operated in a fully open outdoor area with unrestricted airflow.
The 20-foot rule is the minimum safe distance established by the CPSC and confirmed by every major
generator manufacturer. At 20 feet with exhaust pointed away, CO concentrations at the home's openings
drop below dangerous thresholds. At 10 feet or less, CO can enter through closed doors and windows.
Standby generator clearance requirements
Standby (permanent) generators have different clearance rules than portable generators. Typically, they
must be installed 18 inches to 5 feet from the house wall (depending on the model) and at least 5 feet
from any door, window, or intake vent. Always follow the manufacturer's installation manual and your
local building code, which may require greater distances.
Generator Type
Min. Distance from House
Exhaust Direction
Source
Portable (gas/propane)
20 feet minimum
Away from all openings
CPSC, all manufacturers
Standby (air-cooled)
18 in – 5 ft from wall
Per install manual
Manufacturer specs
Standby (liquid-cooled)
5 ft from any opening
Per install manual
NFPA 37, local code
Solar/battery generator
No CO — indoor safe
N/A (no exhaust)
No combustion
Why wind direction matters
Even at 20 feet, wind can carry carbon monoxide toward the house if the exhaust points upwind. Always
position the generator so exhaust points downwind — away from the house and any neighboring occupied
structures. If wind direction changes during operation, reposition the generator.
CO is slightly lighter than air, which means it disperses upward and with the wind. If the wind is blowing
from the generator toward your home, CO can enter through doors, windows, and vents even at 20 feet. The
safest approach is to place the generator downwind of the house and check wind direction before starting
it. If wind shifts during operation, shut down and reposition.
Solar and battery generators: the exception
Solar and battery generators (like the EcoFlow Delta Pro 3, Anker SOLIX F3800, and Bluetti Elite 200 V2)
produce no carbon monoxide because they have no combustion engine. They can be safely operated indoors,
including in basements and living spaces. This is a major safety advantage over gas and propane generators.
Frequently Asked Questions
Can I put a generator on my porch?
No. A porch is too close to the house and is considered a semi-enclosed space. Generators must be at least 20 feet from any door, window, or vent and operated in a fully open outdoor area. A porch does not meet either requirement.
Does the 20-foot rule apply to inverter generators too?
Yes. The 20-foot rule applies to all gas and propane generators regardless of size or type. A 2,200W inverter produces the same carbon monoxide as a 12,000W open-frame generator. Inverter generators are quieter, but CO output is not reduced.
How far should a standby generator be from the house?
Standby (permanent) generators have different clearance requirements specified by the manufacturer and local building code. Typically, they must be 18 inches to 5 feet from the house wall (depending on the model) and at least 5 feet from any door, window, or intake vent. Always follow the manufacturer's installation manual and local code.
Can I run a generator under a deck?
No. Running a generator under a deck, awning, or overhang traps exhaust and allows carbon monoxide to accumulate. The area beneath a deck is considered semi-enclosed. Generators must be in a fully open area with unrestricted airflow.
Which direction should generator exhaust face?
Generator exhaust must always point away from the house — and away from any neighboring homes, tents, or occupied structures. Wind direction matters: if wind blows from the generator toward the house, CO can enter even at 20 feet. Reposition the generator so the exhaust points downwind.
Can I use a generator in an attached garage with the door open?
No. An attached garage is connected to the living space, and CO can enter through the connecting door or wall gaps even when the garage door is open. Garages are never safe for generator operation, attached or detached.