The Outage PlannerBackup power math for homes and RVs

How far should a portable generator be from the house?

By , The Outage Planner · · 9 min read · Generators

Short answer (checked November 1, 2026): put a portable generator at least 20 feet (6 meters) from your house, with the exhaust pointing away from the home and every window, door and vent on that side closed. That is the line drawn by the US Consumer Product Safety Commission, the CDC and Health Canada. Treat 20 feet as the minimum, not the target: government modeling found 25 to 30 feet was where indoor carbon monoxide generally stayed low.

The catch most guides skip is the cord. Moving the generator farther away means a longer extension cord, and a thin cord over a long run wastes power and heats up. Below is where to put the generator, then the cord math that lets you put it there safely.

This is general safety information, not electrical advice. Follow your generator's manual, and use a licensed electrician for any connection to your home's wiring.

Why 20 feet is the floor, not the goal

Carbon monoxide (CO) from a gasoline generator has no color or smell. CPSC estimates that about 100 people die in the US each year from CO poisoning linked to portable generators, and that it can make people unconscious before they notice the nausea or dizziness. Its 2022 report found 81 percent of generator CO deaths happened at homes, and the top reason people were running the generator was a weather-related outage.

The most useful numbers come from computer modeling that the National Institute of Standards and Technology (NIST) did for the CDC:

What NIST modeled Distance from the house What it found
One-story home, open window 15 ft (4.6 m) May not be far enough to keep CO out (NIST Phase 1)
One-story home, open window 25 ft (7.6 m) Peak indoor CO minimal regardless of wind speed or direction
Two-story home 30 ft (9.1 m) Generally low indoor CO, especially with exhaust pointed away (NIST Phase 2)
Two-story home, exhaust away vs toward the house Same distance Maximum indoor CO with exhaust pointed away was only 3 percent of the exhaust-toward case

Two more findings from the same work matter on storm nights. Light, still wind was the worst case because CO lingered by the windows, and wind blowing straight at an open window pushed in more CO than wind at an angle. NIST also notes the CDC reported that up to half of non-fatal generator CO poisonings in the 2004 and 2005 hurricane seasons involved generators run outdoors but within seven feet of the home.

So the practical rule: 20 feet minimum, 25 feet or more for a single-story house, 30 feet or more for a two-story house, and exhaust always pointing away.

Where not to put a generator

CPSC says never run a portable generator inside a home, garage, basement, crawlspace or shed, or on a porch or in a carport, and that opening doors or windows will not provide enough ventilation. Also keep it away from:

The cord math: what it takes to reach 25 feet

Distance only helps if your cord can cover it. Every cord has resistance, so some voltage is lost along the way (voltage drop), and that lost power turns into heat in the cord. Fridge compressors and furnace blowers do not like low voltage.

How we did the math: current (amps) = watts / volts. The current goes out and back, so the wire length is twice the cord length. Voltage drop = amps x wire resistance. Copper resistance at 20°C from the American wire gauge table: 14-gauge 2.525 ohms, 12-gauge 1.588 ohms and 10-gauge 0.999 ohms per 1,000 feet.

Voltage drop on a 120 V generator (US and Canada):

Cord length 14-gauge at 10 A 14-gauge at 15 A 12-gauge at 15 A 10-gauge at 15 A
25 ft 1.3 V (1.1%) 1.9 V (1.6%) 1.2 V (1.0%) 0.8 V (0.6%)
50 ft 2.5 V (2.1%) 3.8 V (3.2%) 2.4 V (2.0%) 1.5 V (1.2%)
100 ft 5.1 V (4.2%) 7.6 V (6.3%) 4.8 V (4.0%) 3.0 V (2.5%)

10 A is about 1,200 W at 120 V, and 15 A is about 1,800 W, the most a standard 15 A household outlet on the generator should carry.

What the table tells you:

  1. A 50-foot, 12-gauge cord is the sweet spot for most homes. It reaches 25 to 30 feet with slack to route around corners and keeps drop at 2 percent even at 15 A.
  2. A 100-foot, 14-gauge cord at full load is the one to avoid. It loses 7.6 V, and the heat in the cord is amps squared x resistance: 15 x 15 x 0.505 ohms = about 114 W spread along the cord.
  3. Generator makers set their own limits. Honda, for example, lists a 50-foot maximum standard outdoor cord for its EU2200i. Check your manual, and if it is stricter than this table, follow the manual.

Use a heavy-duty, outdoor-rated cord with three prongs, and check it for cuts before every use, as the NFPA generator safety tip sheet advises. In Canada, Get Prepared says the cord should be properly rated and CSA-approved.

Example scenario: a fridge, a freezer and the lights

An illustration with stated assumptions, not a real household. A one-story house plans to run a fridge, a chest freezer, a router and some LED lights, averaging about 600 W with short startup surges when the compressors kick in. That is 5 A at 120 V. The generator goes 25 feet out, so the owner buys a 50-foot, 12-gauge cord for the routing. At 5 A, drop is 5 x 0.159 ohms = 0.8 V, well under 1 percent. Even a 15 A load would stay at 2 percent. For fridge sizing, see what size power station runs a fridge; the same running-watt and surge numbers apply to a generator.

The hidden CO leak: how the cord gets inside

Here is the mistake that undoes good placement. People run the cord through a door, window or garage door left open a few inches, and that gap is exactly where CO gets in. CPSC says to close windows and seal off vent openings near the generator or in the path of its exhaust.

Safer options, best first:

Rain, snow and wind

Distance does not mean leaving the generator in a puddle. Health Victoria says to keep it dry, run it on a dry surface under an open, canopy-like structure, and dry your hands before touching it. CPSC adds that you should follow your manual on wet weather, which may include an NFPA-rated non-combustible generator tent or waiting for the rain to pass. The NFPA tip sheet adds one more: do not stand or sit downwind of the exhaust, and if you can smell it, you are breathing it. In snow, clear around the generator and its exhaust so it is not sitting in a drift.

UK and Australia: 230/240 V changes the cord math

UK and Australian generators put out 230 or 240 V, so the same 1,200 W draws about half the current. With half the current, the voltage lost on the same cord halves too, and as a share of the higher voltage it falls to about a quarter. Long leads are much less of a problem, but the distance rules are not.

Pre-storm placement checklist

  1. Pick the spot now, in daylight: open air, 25 to 30 feet from the house, downwind if possible, away from every window, door, vent and your neighbor's house.
  2. Measure the walk from that spot to where the cord enters the house, and buy a cord at least that long in the gauge from the table above.
  3. Point the exhaust away from the house.
  4. Close every window and door on that side.
  5. Test your CO alarms. CPSC says to have battery-operated or battery-backup CO alarms on each floor and outside sleeping areas, tested monthly.
  6. If you are buying, look for CO shut-off. CPSC estimates models certified to PGMA G300-2018 and UL 2201 would cut CO deaths by 86 and 100 percent, and UL 2201 models also have lower CO emissions.
  7. Shut it off and let it cool before refueling, as Health Canada advises.

If an alarm sounds or anyone feels dizzy, sick or confused, get everyone outside and call 911 (999 in the UK, 000 in Australia). Do not go back in to find the source.

What about a CPAP or sensitive electronics?

If the main reason for backup power is a medical device, a battery power station may suit you better, because it makes no CO and can sit indoors. See how long a power station runs a CPAP. Health Canada also notes that battery and solar generators make no carbon monoxide.

Your next step: pick the generator spot and measure the cord run this week, before the next storm. More guides are in Generators.

Sources

Checked November 1, 2026.

Quick answers

How far away from the house should a portable generator be?

At least 20 feet (6 meters) from the house and from any window, door or vent, with the exhaust pointed away from the home. That is the guidance from CPSC, CDC and Health Canada. NIST computer modeling found 15 feet could still let dangerous carbon monoxide into a house, while 25 feet (one-story home) and 30 feet (two-story home) generally kept indoor levels low.

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

No. CPSC says never run a portable generator in a garage, basement, crawlspace, shed or on a porch, and that opening doors or windows will not provide enough ventilation to stop carbon monoxide building up to lethal levels.

What extension cord do I need to put a generator 25 feet away?

A heavy-duty, outdoor-rated, three-prong cord sized for the load. For up to about 15 amps at 120 volts, a 12-gauge cord keeps voltage drop under about 2 percent at 50 feet. A 14-gauge cord works for lighter loads, and 10-gauge is the safe choice at 100 feet or near the outlet's full rating.

Is a generator under a carport or porch roof far enough away?

Not in US or Canadian guidance. CPSC specifically says not to run one on a porch or in a carport, and Health Canada says not in partly enclosed spaces. Use open air at 20 feet or more, and keep it dry with a cover the manufacturer approves.

Dale Becker is the pen name of The Outage Planner's editorial team. Figures come from the manufacturer specs and public sources linked above and were checked on the date shown. Prices and specs change, so confirm before you buy. Example scenarios are illustrations with stated assumptions, not real households. Some links may be affiliate links that pay us a commission at no extra cost to you.