How Far Should a Generator Be From Your House?

Every year, in the days after a big storm knocks out power somewhere in America, the news runs the same story. Not about the storm — about a family that ran a generator too close to the house, or in the garage, or on the porch, and never woke up. As an electrician who has installed backup power for two decades, I can tell you these aren’t freak accidents. They’re the predictable result of one misunderstood fact: the distance between your generator and your house is not a guideline. It’s the safety system.

This guide explains the 20-foot rule properly — where it comes from, why garages and porches never qualify, how the rules differ for standby units, and why exhaust direction matters almost as much as distance.

Why is carbon monoxide the whole ballgame?

A portable generator’s exhaust contains carbon monoxide in concentrations that dwarf a car’s. CO is colorless, odorless, and binds to your blood roughly 240 times more readily than oxygen. You don’t smell it, you don’t see it, and the early symptoms — headache, dizziness, confusion — are easy to mistake for exhaustion after a long, stressful day of storm cleanup. Then you lie down and don’t get up.

The CPSC attributes dozens of American deaths every year to portable-generator carbon monoxide alone, with the toll spiking after hurricanes — and for every death there are far more emergency-room visits for CO poisoning that never make the news. Nearly all of them share a setup: the generator was inside something, under something, or a few feet from an open window.

Here’s the part that surprises people: you cannot ventilate your way out of this. Opening the garage door doesn’t fix it. A box fan doesn’t fix it. CPSC testing has found deadly CO levels in garages with the door fully open, because the gas accumulates faster than passive airflow clears it, and it migrates into the living space through the shared door, the ceiling, and every little penetration in between. Distance is the control that works.

What exactly is the 20-foot rule?

Both the CDC and the U.S. Consumer Product Safety Commission give the same instruction for portable generators:

• At least 20 feet from the house (and from any other occupied building).
• Exhaust pointed away from the house.
• Never inside — not the house, garage, basement, crawlspace, or shed — and not on a porch or under a carport either.

Twenty feet is roughly the length of two pickup trucks. It feels far when you’re sizing up your yard, and it feels farther when you’re thinking about extension cords — but the number exists because CO concentration falls off with distance, and 20 feet puts the exhaust plume far enough out that normal air movement dilutes it before it reaches your walls and windows.

Measure from the generator to the nearest part of the building, not to your back door. And treat “the house” as including attached garages, covered porches, and three-season rooms — anything with a roof and a path into your living space.

Why isn’t a garage, carport, or porch ever okay?

Because each one defeats the distance in a different way:

• Garage: an enclosed box attached to your home, with a door (often left cracked or opened repeatedly) straight into the house. The worst possible choice, and statistically the deadliest.
• Basement or crawlspace: CO rises through the floor and chases the same paths your pipes and ducts take — which is to say, everywhere.
• Covered porch or carport: feels “outside” but the roof traps exhaust and pools it against the wall and the door you keep opening. Semi-enclosed is enclosed enough.
• Under a deck or awning: same trapping problem, plus you’re now heating a structure with an exhaust pipe.

The mental test is simple: if the spot has a roof over it or walls around most of it, it counts as inside.

How far should it be from windows, doors, and vents?

The rule is about openings, not just the building. Twenty feet from the wall but directly under an open bedroom window is a failure. Walk your property and look for:

• Windows and doors, especially any left open for “fresh air” during an outage.
• Dryer vents and bathroom/kitchen exhaust vents — gaps into the wall system.
• Soffit vents and attic intakes. Warm exhaust rises. A generator tucked under an eave can feed CO into the attic through the soffits, and from there it spreads through the whole house.
• Your fresh-air intake, if your HVAC has one.

Also think about wind. On a still night, exhaust drifts and pools in low, sheltered spots. With wind, the plume goes where the wind says — including straight back at the house if the generator sits upwind of it. When you pick your spot, pick it for the exhaust’s sake: generator downwind of the house when you can, exhaust aimed away and slightly outward, nothing overhead to trap the plume.

What if your yard is smaller than 20 feet?

Townhomes, zero-lot-line suburbs, and city lots run into this honestly: there may be no legal spot a full 20 feet from every structure. Handle it in this order:

1. Maximize the distance you have. Fifteen honest feet with the exhaust aimed away beats twenty feet with the exhaust aimed at a window. Distance and direction work together.
2. Spend the difference on detection. If you can’t buy the full 20 feet, your CO alarms stop being a backup and become the primary warning system — one on every level, outside every sleeping area, in date, battery-backed. Test them the day you test the generator setup, not someday.
3. Rethink the tool. A permanently installed standby unit plays by closer, code-governed clearances (next section). A power station doesn’t play the CO game at all. For some small lots, the right answer to “where does the portable go?” is “it doesn’t — we chose a different system,” and there’s no shame in that answer. It’s the one that keeps everyone asleep safely.

What never makes the list: splitting the difference by putting it in the garage “only while it rains,” or on the porch “with a fan.” The compromised setups are the ones in the news stories.

Why can a standby generator sit so much closer?

Because it’s not a portable. A standby (whole-house) generator is a permanently installed, listed appliance in a weatherproof enclosure, placed under a standard — NFPA 37 — and the manufacturer’s tested installation instructions. The key figure from the standard: exhaust at least 5 feet from any opening in the building. The cabinet itself is often installed 18 inches to a few feet off the wall, per its listing, with the exhaust outlet oriented away from windows and doors.

Two things to understand about that difference:

1. The clearance comes from engineering, not luck. The enclosure, exhaust routing, and placement were tested as a system, and a permitted installation gets inspected against code. Your portable on the patio has none of that.
2. “Closer is allowed” is not “distance doesn’t matter.” Installers still can’t park a standby unit under your bedroom window — the 5-feet-from-openings rule, local code, and the manual all constrain the pad location. If you’re planning a standby install, the complete home backup power guide covers how placement fits the bigger project, and the transfer switch versus interlock guide covers the electrical side.

What about your neighbors?

CO doesn’t respect property lines. If your generator is 20 feet from your house but 8 feet from your neighbor’s open window, you’ve exported the problem. In dense neighborhoods this takes thirty seconds of thought: aim the exhaust along your own lot, away from both homes’ windows, and if you share a wall (townhomes, duplexes), coordinate — your neighbor’s “fresh air” window may be right where your exhaust wants to go.

Apartment and condo residents, listen carefully: a balcony is inside for these purposes. Generators on balconies have killed people in the unit and the units nearby. If your building loses power, a portable generator is simply not an option for you — a portable power station is the safe indoor tool for keeping the essentials alive.

How do you power the house from 20 feet away?

The legitimate objection is the cords. Twenty feet of distance means your extension runs are 25–40 feet by the time they snake through a door, and cord quality stops being optional:

• Use heavy-gauge outdoor cords. For a 30–50 foot run carrying real loads, 12-gauge is the floor and 10-gauge is better. A cheap 16-gauge cord turns voltage into heat along its whole length, starves motors (your sump pump will not forgive this), and becomes a hazard itself.
• Better: an inlet box. A permanently installed power inlet on the outside wall, wired to a transfer switch or interlock at your panel, lets one fat generator cord replace the nest of extension cords through a cracked door. It’s the setup I install most, and it keeps the door shut — which also keeps CO out. See the transfer switch versus interlock comparison for how the two approaches differ.
• Mind the trip-and-crush points. Cords across driveways get driven over; cords through doorways get pinched. Route them deliberately, not hopefully.

If you’re running the generator through a multi-day outage, placement discipline pairs with fuel discipline — the storm preparedness checklist covers both, and the fuel consumption guide helps you plan how much gasoline that distant generator will actually drink.

Mike’s placement checklist

Print this on the inside of your head:

1. 20 feet minimum from the house — measured to the building, not the back door.
2. Exhaust pointed away from your house, your neighbors’ windows, and every vent you can find.
3. Never under a roof — no garage, porch, carport, deck, or awning, door open or not.
4. Nothing overhead to trap the plume; watch soffit and attic vents.
5. Downwind when possible, and away from low spots where exhaust pools.
6. CO alarms on every level, battery-backed, in date. The alarms are what catches the mistake you didn’t know you made.
7. Cool before refueling, always — and let it cool before you move it anywhere, too.

The generator is the most useful dangerous tool most homeowners own. Twenty feet and an exhaust pointed the right way is nearly the whole difference between “the machine that saved our week” and the other kind of story. Keep the distance.

Practical note: if you’re placing a generator to run in bad weather once it reaches its spot, the companion guide on running a generator safely in the rain covers covers, cords, and wet-weather rules.