A portable generator should be at least 20 feet from any window, door, or vent on your home. FEMA and the CDC both recommend this minimum distance, with the exhaust pointed away from the building. For stationary (permanently installed) generators, safety officials have recently pushed the recommendation even further to 25 feet.
Why 20 Feet Is the Minimum
Generators produce carbon monoxide, an odorless, colorless gas that can kill within minutes at high concentrations. The 20-foot rule exists because CO can drift toward your home and seep inside even through gaps you wouldn’t think about: closed windows, dryer vents, the space around a window AC unit, or the gap under a door. A CPSC investigation of fatal and near-fatal CO poisoning incidents found that in 17 homes, exhaust entered through closed doors, closed windows, exhaust fan vents, dryer vents, or from underneath raised houses.
Carbon monoxide doesn’t need an open window to get inside. At 400 parts per million, a standard home CO alarm takes 4 to 15 minutes to activate. At 150 ppm, it can take 10 to 50 minutes. That delay means dangerous levels can build up in your home before anyone realizes it. The 20-foot distance, combined with pointing the exhaust away from the house, gives CO enough space to disperse in open air before reaching concentrations that could infiltrate your living space.
Windows Aren’t the Only Openings That Matter
People tend to focus on windows and doors, but homes have dozens of openings that can pull in exhaust fumes. Building guidelines from jurisdictions that regulate generator placement list soffit vents, gable vents, ridge vents, dryer exhausts, weep holes, and crawlspace vents as entry points for CO. Some local codes require that no opening of any kind exists within 5 feet of a stationary generator, extending in all directions up past the roofline.
If your home is raised off the ground with a crawlspace, the area underneath can trap CO and push it up through the floor. Sealing off crawlspace access near the generator is a standard precaution in areas where raised homes are common. The practical takeaway: don’t just measure 20 feet from the nearest window. Look at every potential opening on the side of your house where you plan to place the generator, including vents you may not have noticed before.
Exhaust Direction Matters as Much as Distance
Even at 20 feet, a generator with its exhaust pipe aimed directly at your house creates risk. The exhaust should always face away from the building. Wind direction plays a role too. FEMA specifically recommends placing your generator downwind from open doors, windows, and vents, meaning the wind should blow exhaust away from your home rather than toward it.
This can be tricky during storms when wind shifts direction. If you’re running a generator during a hurricane or severe weather, check periodically that conditions haven’t changed in a way that pushes fumes toward your home. A battery-operated CO detector inside your house is essential backup regardless of placement.
Stationary Generators May Need Even More Distance
If you have a permanently installed standby generator, the National Fire Protection Association currently recommends a minimum of 5 feet from your home. However, safety officials have recently warned that this standard may not be sufficient. A new federal recommendation suggests stationary generators should be placed at least 25 feet from homes. The NFPA has convened a technical committee to review whether the 5-foot guideline needs to be revised upward.
Many municipalities already use NFPA codes as their local building standard, so if you’re installing a standby generator, check your local requirements. Your jurisdiction may enforce the older 5-foot rule, the newer 25-foot recommendation, or something in between.
Keeping Your Generator Dry Without Bringing It Closer
Rain and wet conditions are the main reason people are tempted to move a generator closer to the house, under an eave or into a garage. Never run a generator in a garage, carport, breezeway, or any enclosed or semi-enclosed space. OSHA recommends using a canopy to keep a generator dry while leaving it in its safe outdoor location. Generator tents and covers designed for this purpose are widely available.
Whatever cover you use, maintain at least 3 to 4 feet of clear space on all sides and above the unit. Generators produce significant heat, and restricting airflow creates both a fire risk and a CO buildup risk even outdoors.
Running Power Cords Over 20 Feet
Placing a generator 20 or more feet from your home means you need extension cords that can handle the distance without losing significant power. Voltage drop increases with cord length and decreases with thicker wire. For a typical 30-amp setup on a 100-foot cord, 8-gauge wire keeps power loss around 2.5%, which is within the safe range. A 10-gauge cord at the same amperage is best kept under about 50 feet to stay below a 2% voltage drop.
Use outdoor-rated, heavy-duty cords designed for generator use. If you need to run power farther than 50 feet at high amperage, step up to a thicker gauge. Running an undersized cord over a long distance doesn’t just waste electricity; it generates heat in the wire, which can melt insulation or start a fire.
Noise Drops Significantly With Distance
One benefit of the 20-foot rule: it also reduces noise inside your home. Sound levels drop predictably with distance. A generator producing 66 decibels at 23 feet (roughly the volume of a normal conversation) drops to about 57 decibels at 46 feet and 48 decibels at 125 feet. If a solid object like a fence or shed sits between the generator and your home, you can expect an additional 5-decibel reduction.
For context, 48 decibels is about the level of a quiet library. So placing your generator at or beyond the recommended 20 feet doesn’t just protect you from CO poisoning; it also makes sleeping with a running generator far more tolerable during an extended outage.
CO Shutoff Sensors on Newer Generators
Newer portable generators increasingly come equipped with built-in carbon monoxide sensors that automatically shut the engine down when CO levels get too high. The proposed federal safety standard would require these sensors to trigger a shutoff when CO reaches 400 ppm instantly or 150 ppm over a 10-minute average. After a shutoff, the generator would display a red warning light for at least 5 minutes.
These sensors are a valuable safety layer, but they’re not a substitute for proper placement. A generator with a CO shutoff that trips repeatedly because it’s too close to a wall or window isn’t protecting you; it’s telling you the placement is wrong. Treat the 20-foot, exhaust-away rule as the primary safeguard, and a CO sensor as the backup that catches what distance alone might miss.