Generator Carbon Monoxide Safety: Distance Rules and What Never to Do

A portable generator needs to run at least 20 feet from your house, with the exhaust pointed away from every window, door, and vent. A permanently installed standby generator has more room to work with under the national fire code, but a 2025 federal safety review now recommends pushing even those units out to 25 feet whenever your lot allows it. Distance is the single biggest factor in whether carbon monoxide from a generator stays outside or ends up in your Wilmette, Northbrook, or Glenview living room.

This guide covers both generator types, what Illinois already requires for carbon monoxide alarms, and the placement mistakes that keep showing up in poisoning cases nationwide.

Why Generator Carbon Monoxide Is So Dangerous

Short answer: Carbon monoxide from a gas or gasoline generator has no color, smell, or taste, and it can build to a fatal concentration in a closed or partly closed space in minutes. The U.S. Consumer Product Safety Commission (CPSC) says hundreds of people die and thousands more get sick from generator carbon monoxide every year nationwide.

A generator engine produces far more carbon monoxide per hour than a car does, and unlike a car exhaust pipe pointed at open road, a generator sitting near a house can push that gas straight toward windows, vents, and door gaps. Cold weather makes it worse, because North Shore homeowners are more likely to seal up doors and windows exactly when a generator is most likely to be running after an ice storm or a ComEd outage.

Portable Generators: How Far From the House?

Short answer: Run a portable generator outside only, at least 20 feet from your house, with the exhaust aimed away from doors, windows, and vents. Never run one in a garage, breezeway, porch, or basement, even with a door or window open.

The CPSC's core guidance is direct: operate portable generators outside only, at least 20 feet away from the house, and direct the exhaust away from the home and any other buildings. The CDC gives the same 20 foot figure for keeping a portable unit clear of doors, windows, and vents. Twenty feet is roughly the length of one and a half parking spaces, which is often farther than it looks once you are standing in a yard during a storm.

Look for a portable model with an automatic carbon monoxide shutoff, a feature the CPSC recommends asking retailers about by name. These units sense a dangerous buildup of CO in the surrounding air and shut the engine down before it becomes lethal, which matters most in a tight North Shore yard where 20 feet of clearance is not always easy to find.

Standby Generators: NFPA 37 vs. the New Federal Guidance

Short answer: NFPA 37, the national fire code for stationary engines, sets a minimum of 5 feet between a standby generator and any opening in your house. A 2025 federal safety report recommends going much farther, up to 25 feet, after finding that generator exhaust reached homes well beyond the old 5 foot minimum.

Your installer sizes and sites a standby unit under NFPA 37, which requires generators installed outdoors to sit at least 5 feet from openings in the wall and at least 5 feet from a structure with combustible siding, unless the enclosure meets specific fire rated exceptions. Our Illinois generator permit guide covers how that clearance rule fits into your village's permit review.

That 5 foot figure is now under real pressure. The CPSC studied 105 homes near New Orleans in the days after Hurricane Ida in 2021 and found carbon monoxide from stationary generators had entered every one of them, with people in a dozen of those homes showing symptoms of CO poisoning. Some of that exhaust had traveled at least 25 feet from the generator and spread sideways at least 6 feet before working its way into the house. Based on that data, federal regulators issued new guidance in 2025 recommending stationary generators sit at least 25 feet from a home whenever the lot has room for it, five times the traditional NFPA 37 minimum.

Why a Garage or Carport Is Never Safe

Short answer: A generator should never run in a garage, even with the door wide open. Carbon monoxide builds up faster than an open garage door can vent it, and an attached garage shares walls, ducts, and door gaps directly with your living space.

The CPSC is unambiguous on this point: never use a generator indoors or in any enclosed or partially enclosed space. A garage with the door open is still a partially enclosed space. Three walls and a roof trap exhaust long enough for concentrations to climb into a dangerous range, and any door between the garage and the house, even a closed one, is rarely airtight enough to stop the gas from drifting through.

This is also why a carport, breezeway, screened porch, or the space under a raised deck are all off limits. If it has a roof and more than one wall, treat it like an enclosed space.

Carbon Monoxide Alarms: What Illinois Law Requires

Short answer: Illinois law already requires a working carbon monoxide alarm within 15 feet of every room used for sleeping in any home with fuel burning equipment or an attached garage, which describes nearly every North Shore house.

The Illinois Carbon Monoxide Alarm Detector Act (430 ILCS 135) has been in effect statewide since January 1, 2007. It requires at least one CO alarm within 15 feet of every sleeping room in homes that burn fossil fuels for heat, ventilation, or hot water, or that connect to an attached garage. A generator running anywhere near the house, portable or standby, is exactly the kind of source this law was written for.

Battery backed alarms matter here specifically because a CO emergency often happens during the same power outage that has your generator running in the first place. A plug in alarm with no battery backup goes dark right when you need it most.

Warning Signs and What to Do

Short answer: Headache, dizziness, weakness, nausea, vomiting, sleepiness, and confusion are the early signs of CO poisoning. If anyone in the house feels these symptoms while a generator is running nearby, get outside into fresh air immediately and call 911.

These symptoms can look like a flu or simple exhaustion at first, which is part of what makes carbon monoxide dangerous. If more than one person in the house feels sick at the same time during or after a generator has been running, treat that as a strong signal, not a coincidence. Do not go looking for the source. Get everyone outside first, then call for help.

Our power outage checklist covers the broader steps to take once your household is safe, from food safety to sump pump backup. If anyone in your home relies on powered medical equipment, our guide to power outages with medical equipment covers additional precautions that matter here too.

What to Never Do With a Generator

• Never run it indoors. Not in a garage, basement, crawlspace, or any room of the house, regardless of ventilation.
• Never run it in a partially enclosed space. A garage with the door open, a screened porch, or a carport all count.
• Never aim the exhaust toward your house or a neighbor's. Point it away from every structure, not just your own windows.
• Never rely on open windows or fans to clear CO. Airflow reduces concentration slowly; a generator produces it fast.
• Never skip the CO alarm. Illinois law requires one, and it is the only warning system that works while everyone is asleep.
• Never guess at placement. Compare your yard against the standby vs. portable generator distance rules above before you plug anything in.

Frequently Asked Questions

How far should a generator be from my house to avoid carbon monoxide?

A portable generator should run at least 20 feet from your house, with the exhaust pointed away from windows, doors, and vents, per CPSC and CDC guidance. For a permanently installed standby generator, NFPA 37 sets a minimum of 5 feet from openings in the wall, but a 2025 federal safety report recommends placing stationary units as far as 25 feet away whenever your lot allows it.

Can carbon monoxide from a generator get into my house through a window?

Yes. A federal review of homes near Hurricane Ida found carbon monoxide entering 105 houses through windows and soffits, even when the generator sat outside. That is why the newer federal guidance pushes stationary generator placement out to 25 feet instead of the older 5 foot minimum.

Is it safe to run a generator in a garage with the door open?

No. The CPSC is clear that a generator should never run indoors or in any enclosed or partially enclosed space, including a garage with the door open. Carbon monoxide builds up faster than an open door can vent it, and it can still drift into the attached house.

Do I need a carbon monoxide detector if I have a generator?

Yes, and Illinois law already requires one. The Carbon Monoxide Alarm Detector Act requires a working CO alarm within 15 feet of every room used for sleeping in any Illinois home with fuel burning equipment or an attached garage, which covers nearly every North Shore house.

What are the first signs of carbon monoxide poisoning from a generator?

Headache, dizziness, weakness, nausea, vomiting, sleepiness, and confusion are the early symptoms the CPSC lists. If anyone in the house feels these symptoms while a generator is running, get outside into fresh air immediately and call 911 before doing anything else.

A properly sited standby generator installation, done by a licensed electrician who knows both NFPA 37 and the newer federal guidance, removes most of this risk before it ever becomes a decision you have to make during a storm. Fill out the form below and we will connect you with one local licensed and insured electrician who can site your system correctly the first time.