Generator placement: exhaust, openings, and the neighbor

The kilowatts are the easy argument. The hard one is the rectangle of dirt next to the house: far enough from windows and soffits that exhaust does not come back inside, far enough from the lot line that the neighbor does not live with a small engine, and close enough to the gas meter and panel that the trench does not eat the job. A 22 kW unit in the wrong alcove is a carbon monoxide problem with a transfer switch.

If you have not picked a machine yet, start with battery vs standby generator. If you already know you want gas, sizing without the sales chart is how big, and natural gas vs propane vs diesel is the fuel. Stay here when the live question is where the pad goes.

This is not a diagnosis page. If a CO alarm sounds, get everyone outside to fresh air and call 911. CPSC lists headache, dizziness, weakness, nausea, vomiting, sleepiness, and confusion as the symptoms people miss because they look like the flu.

CPSC: carbon monoxide

What does a bad location actually cost?

HomeGuide’s 2026 whole-house generator guide puts a typical standby at $6,000 to $11,000 installed (unit plus labor), or $9,500 to $24,000 when the run is long or the unit is over 20 kW. Placement is how you land in the second band. Their factor table is the map: gas line $12 to $25 per foot (they also cite $15 to $50+ on the gas-line page), electrical wiring $6 to $8 per foot, a 3 to 4 inch precast pad $150 to $400, permits $80 to $450. Push the unit 30 extra feet to clear a bedroom window and you bought trench, not kilowatts.

HomeGuide: whole house generator cost

HomeGuide also says most generators run 60 to 70 decibels from 25 feet, in the same neighborhood as a central air conditioner, and that city lots can put that number over a local noise ordinance at the property line. There is no federal standby noise standard. The inspector, if they care, measures at the lot line, not at the enclosure.

A portable is a different rectangle. HomeGuide puts the machine at $500 to $2,500, plus $400 to $1,300 for a transfer switch. The inlet box is how that power gets inside. Placement for a portable is CPSC’s outdoor rule, not a pad drawing.

What does NFPA 37 actually require?

NFPA 37 is the fire standard for stationary combustion engines outdoors. Generac’s clearance article, written for their residential standby line, is the version installers quote on air-cooled jobs. Local code still wins if it is stricter.

Generac’s published NFPA 37 picture:

• 5 ft from openings in walls: operable windows, doors, vents, window wells, or other openings.
• 18 in from the back of the generator to a stationary wall, only on units marked with the Southwest Research Institute (SwRI) logo. That reduced rear clearance is a fire test, not a CO test.
• 5 ft of clearance above the generator. Do not slide it under a wooden deck or platform. Generac says that in so many words.
• 3 ft at the front and both ends, including trees, shrubs, and bushes, so air can get in and a tech can take a panel off.
• Units without the SwRI logo: 5 ft from combustible materials and 3 ft from non-combustible, not the 18-inch rear shortcut.

Generac: clearance requirements

NFPA 37

The International Code Council’s writeup of CPSC’s June 2025 stationary-generator report is the part the fire standard does not say. NFPA 37 section 4.1.4 is about fire: five feet from openings and from combustible walls, with exceptions if the wall is one-hour rated or a fire test says the enclosure will not ignite the house. UL 2200, the product safety standard for stationary generators, does not require CO infiltration distances. Five feet can be a legal fire install and still put exhaust into the living space.

ICC: stationary generators and CO

Generac’s own article agrees in one sentence: a unit installed to NFPA, including the SwRI offset, may still allow CO into the structure, and it may need to sit farther than the fire distances.

Why five feet is not a CO guarantee

After Hurricane Ida in 2021, CPSC looked at 256 New Orleans-area homes that reported indoor CO during the outage. The home’s stationary generator was the source in 105 of those homes. A portable was the source in 65. Of 49 homes where they had a clearance number, 41 had more than five feet, and 13 of those had 10 feet or more. The CO alarms still went off. Twelve homes had people with poisoning symptoms.

Where the exhaust got in, when they could tell: mostly soffit vents. Also dryer vents, the gap around a window AC, under the house, and through closed doors and windows. One installation pointed exhaust along the wall and it traveled at least six feet. Another had a brick wall a few feet off the exhaust side that lofted the plume 15 to 20 feet into second-floor windows and the soffits above them. One unit exhausted from under the lid toward the house and still reached soffits 26 feet away.

That is why “we met 5 ft” on the permit drawing is not the whole conversation. Ask which way the exhaust points, what is above it (soffits, ridge vents, attic intakes), and whether a fence, AC condenser, or courtyard will trap the plume. Generac’s entry-point list is the same idea: garage doors, attic and soffit vents, basement windows and crawl spaces, furnace intakes, wall cracks, dryer vents, HVAC outdoor air intakes, and corners that hold exhaust.

Point the exhaust away from the house and away from the neighbor’s openings. Do not aim it at the AC condenser that will blow it toward a window. Do not hide the unit in an alcove because the HOA hates the look. Restricted airflow is how fumes collect.

Portables are a different 20 feet

A standby on a pad is not a portable in the driveway, and CPSC’s consumer rule is for the machine you wheel out. Never run a portable inside the house or garage, even with the door open. Use it outside only, at least 20 feet from the home, exhaust facing away. More than 100 of the 200-plus annual U.S. consumer-product CO deaths CPSC counts are linked to portables. One portable, they say, can put out as much CO as hundreds of cars.

That 20-foot cord run is why the inlet belongs on an exterior wall and the generator sits in the open, not against the siding under a window. If 20 feet puts you in the neighbor’s hedge, you need a longer listed cord and a different patch of yard, not a shorter rule.

What about the neighbor?

NFPA 37 does not set a property-line distance. That is zoning, HOA, and the noise ordinance. HomeGuide’s “where should it go” line is five feet from openings and flammable material, plus a reminder that 60 to 70 dB at 25 feet may be too loud on a tight city lot. Some towns publish accessory-equipment setbacks (five feet from a side lot line is a number you will see; it is not universal). Ask planning, not the generator brochure.

A side yard that satisfies 18 inches to your brick wall can still put the enclosure three feet from the neighbor’s bedroom window. Their opening is an opening. Treat it like yours.

Screening is allowed when it does not become a box. Generac wants 3 ft at the front and ends, including shrubs. A solid fence a foot off the exhaust is a plume trap. If the HOA wants it hidden, use the setbacks in the manual as the inside of the screen, not the outside.

Exercise hour is how you meet the neighbor before the ice storm. Standby units need a weekly test. Put it in daytime if the ordinance cares about nights. The quiet-spec page in the queue is the dBA-at-23-feet argument. This page is: do not put the loud face on their patio.

What should the site plan on the quote show?

1. Pad location, with dimensions to the nearest wall, the nearest opening (window, door, vent, window well, dryer, soffit), and both lot lines.
2. Exhaust direction, labeled. Not “along the house because the gas stub is there.”
3. Overhead clearance. No deck, no low soffit, Generac’s 5 ft above.
4. SwRI logo or not, so you know whether 18-inch rear fire clearance even applies.
5. Gas meter and panel distances, because HomeGuide’s per-foot gas and wire numbers are how a pretty location becomes a $24,000 job.
6. Pad spec: level, noncombustible, the $150 to $400 precast band or a poured equivalent. Drainage and downspouts aimed away. Generac calls out sprinklers, roof runoff, and sump discharge.
7. CO alarms: CPSC wants them on every level and outside sleeping areas, battery or battery backup, interconnected if you can. Louisiana changed the IRC after Ida so a standby install requires CO alarms. Your town may already require them. Put them on the bid anyway.
8. Permit: electrical, gas, maybe mechanical. HomeGuide’s $80 to $450 is the paper. The drawing is what the inspector walks.
9. Portable jobs: inlet location, cord length to a spot that is 20 feet out with exhaust away, not a patio against the siding.

If the drawing only shows “left of AC, 18 in off wall,” it is a fire sketch. Ask for openings and exhaust.

How does this go wrong?

The unit sits 18 inches off vinyl siding under a bedroom window because that is where the gas tee was. Fire clearance might pass on an SwRI box. The window is an opening. The soffit above it is how Ida’s cases got indoors.

Exhaust points along the house so the plumber did not turn the enclosure. The plume follows the wall into the next window.

A fence and the AC condenser make a courtyard. Fumes sit there on a still night.

A portable lives in the garage “just while it rains,” which is the CPSC fatality pattern.

The HOA screen is a three-sided box with no 3 ft service aisle, so the first oil change is a panel that will not come off, and the exhaust has nowhere to go.

Nobody talks to the neighbor whose patio is eight feet from the exhaust. The ordinance gets involved after the first weekly exercise.

How do I decide this week?

1. Walk the yard with a tape and mark every opening, soffit, dryer vent, and furnace intake, not just the nearest window.
2. Pick a pad that can take Generac’s 5 ft from openings, 3 ft at the service sides, 5 ft overhead, and the SwRI rear rule only if the data plate actually says SwRI.
3. Face the exhaust away from your house and the neighbor’s openings, and add distance if a wall, fence, or condenser would loft or trap the plume. Five feet is the fire minimum, not a CO guarantee.
4. Measure to the lot line and ask planning what accessory-equipment setback and noise limit they use. Do not take “10 feet” from a forum if your town never wrote it.
5. Price the extra gas and wire feet on HomeGuide’s $12 to $25 and $6 to $8 bands before you fall in love with the far corner of the lot.
6. If the machine is portable, budget a listed inlet and a cord that actually reaches 20 feet out, exhaust away, and do not run it in the garage.
7. Put CO alarms on every level and outside bedrooms on the same invoice as the pad, because the clearance drawing will not save you if the plume still finds a soffit.