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Generator noise: the 67 dB at 23 feet is not the fence
A 67 dB(A) standby rating is usually measured 23 feet from the front of the box at normal load. The town, if it cares, measures at the lot line, often at night. Here's what that sticker means, why weekly exercise is the sound the street actually learns, and what has to be on the bid before anyone pours.
You’ve got a standby bid in front of you. Somewhere it says 67 dB, or “whisper quiet,” or it doesn’t mention sound at all.
That number isn’t what your neighbor hears through a bedroom window, and it isn’t what the town measures at the fence, if the town even measures.
You’re trying to figure out whether the pad on the sketch will pass as a neighbor. Start with what the sticker actually is, then look at how far the lot line really is, then make them put the exercise window on the bid before anyone sets concrete.
Fire, exhaust, and openings still belong on the placement guide. Kilowatts still belong on sizing without the sales chart.
What the quiet number is trying to say
Decibels, written dB(A) when they’re A-weighted to roughly match how ears hear, are how loud something is. The scale isn’t like inches. Ten extra dB is a big jump, not a 10 percent bump.
Makers print a small number because quiet sells. Generac publishes most air-cooled standby ratings from 23 feet, which is 7 meters, from the front of the unit at “normal load.” A common 22 kW Guardian line is 67 dB(A) on that recipe.
Generac’s own support article is blunt: there is no standardized way to measure exact sound output, the chart is approximate, and other sides of the box can read higher depending on how it’s installed. They don’t publish dB(A) for portables at all, because load, size, and the yard change the number.
The 16/20/22 kW Guardian spec sheet matches that 22 kW line: 67 dB(A) at 23 ft at normal load, and 57 dB(A) in Quiet-Test, which is the low-speed weekly exercise. On that sheet Quiet-Test runs 5 minutes. Footnote: sound from the front; other sides may be higher.
Generac: 16/20/22 kW Guardian spec sheet (PDF)
Kohler doesn’t use the same microphone recipe. The 20RCA spec lists an 8-point logarithmic average of 66 dB(A) during weekly exercise and 70 dB(A) during full-speed diagnostics and normal operation, all at 23 ft. The published figure is the lowest of the eight points around the box, while Generac’s 67 is the front of the unit at normal load. If one bid quotes Kohler and the other quotes Generac, get both recipes in writing before you pick a winner.
If one bid is “67 dB, whisper quiet” and another is “70 dB, too loud,” ask both dealers which distance, which side of the box, which load, and whether that’s exercise or an outage. You can’t compare two envelopes on sound until both name those.
The factory test isn’t the town’s meter
The number on the spec sheet is a laboratory distance. It was taken 23 feet from the front of the enclosure, not at your fence at 2 a.m.
Your town, if it cares, measures A-weighted sound pressure at a receiving property line, often at night. That’s a microphone at the fence of the person who might complain.
There’s no federal standby noise cap that matches a brochure. Towns write their own. Some publish a number at the property line. Some use a nuisance clause with no number at all. Some exempt generators during an outage and still regulate the weekly test. Pull the PDF for your town, and don’t let a national “whisper quiet” headline stand in for it.
Montgomery County, Maryland, is a worked example, and it isn’t your rule unless you live there.
The county’s residential limits are 65 dBA daytime and 55 dBA nighttime at the receiving property, measured outside at the property line. They treat standby generators as 24-hour sources that have to meet the nighttime 55 dBA number. The ordinance doesn’t recognize the term “emergency generator.” They also grant a 2.5 dBA allowance for meter error, so the practical nighttime target is 57.5 dBA or lower.
They don’t pick a brand for you. The property owner is on the hook.
Montgomery County DEP: noise control
The county even writes the distance rule of thumb on that page: if the level is 62 dBA at 7 meters, it would be about 56 dBA at 14 meters and 50 dBA at 28 meters. They measure at the complainant’s closest property line, not at the enclosure.
Sound from a small source in open air drops about 6 dB each time you double the distance. That’s a driveway check. Don’t treat that math as a permit.
Walk one pad
A 22 kW Guardian at 67 dB(A) at 23 feet is already 12 dB over that 55 dBA night cap if the lot line is 23 feet from the front of the unit.
Double the distance to 46 feet and you only get about 6 dB back, so you’re still around 61 in open air, still over 55.
A wall, a fence, a house corner, or a bounce off vinyl siding will move the number the other way. An alcove against brick, or a box under a deck you were told not to use anyway, throws sound at the lot line that a driveway install doesn’t.
The gap on the install drawing is for exhaust, service, and fire clearance. That’s not the same as “far enough from the neighbor.” Keep those inches on the placement guide. A sound wall that blocks exhaust or service access is a failed install even if it’s quieter.
HOA rules can be tighter than the county. The county might allow 55 dBA at night and still lose to a covenant that says 50, or “no generators,” or “exercise only 10 a.m. to 2 p.m. weekdays.” Get that paper before the pad.
Weekly exercise is the sound the street actually learns
Quiet-Test, if the control has it, is a low-RPM weekly jog. An outage that holds the air conditioner and the well is “normal load” or worse.
Generac Quiet-Test on the 22 kW sheet is 57 dB(A) at 23 ft for 5 minutes. Kohler 20RCA exercise is 66 dB(A) at 23 ft, and their full-speed number is 70. Kohler’s unloaded weekly exercise on that sheet runs 20 minutes, not 5.
The neighbor who complains in July is often complaining about Tuesday at noon, not the ice storm. Put the exercise window on the quote, in writing, in the hours your ordinance or HOA allows.
A farther pad, a different machine, or a battery
HomeGuide’s installed standby band is still $6,000 to $11,000 typical, or $9,500 to $24,000 when the run is long or the unit is over 20 kW. The quiet claim didn’t change the trench.
HomeGuide: whole house generator cost
If the open-air math still overshoots the night cap at the line, the next move is a farther pad, a barrier an acoustics person will stand behind, or a different machine, this week. Relocating after the gas and wire are in is the expensive version of the same decision.
Liquid-cooled Kohler RCL literature publishes lower exercise/run pairs. Their 24RCLA sheet shows an 8-point average around 55/61 dB(A) at 23 ft. Those units are a different building: bigger pad, more money.
Kohler 24–60 kW RCL brochure (PDF)
A home battery is silent at the lot line because there’s no engine. One Powerwall-class pack is still about 13.5 kWh, which is hours, not a three-day ice storm. Don’t buy silence if you needed runtime. If you’re still picking a machine, start with battery vs standby.
A construction-site open frame in the driveway is a different complaint than a closed aluminum box on a pad. Don’t use the Guardian 67 to defend a portable. HomeGuide’s portable band is $500 to $2,500 for the machine plus $400 to $1,300 for a transfer switch.
What has to be on the bid before anyone pours
What’s the exact model, and what’s the factory sound number? You want dB(A), distance (usually 23 feet / 7 m), which side of the unit, and load: normal, no load, or Quiet-Test, with a link to the spec sheet.
Which night number in your town did they use, and is weekly exercise exempt? You want the ordinance name, not “we do this all the time.”
How many feet from the pad to each lot line, and to the nearest bedroom window, yours and theirs? Measure from the front and from the loud side.
When does it exercise: day of week, start time, duration? Generac Guardian Quiet-Test is 5 minutes on the 16/20/22 kW sheet. Kohler 20RCA’s unloaded weekly exercise is 20 minutes. Put it in the hours the ordinance allows.
If a neighbor complains, who comes back with a meter, who pays for a barrier, and is a barrier even legal next to the exhaust?
If this 67 dB(A) box can’t make the night number at this lot line, what’s the fallback: a farther pad, a quieter enclosure, or a battery on the essentials box, as separate jobs, not “we’ll see.”
If two bids copy the same spec footnote and the third says “whisper quiet, 50 dB” with no distance, the third invented a microphone.
How do I decide this week?
Pull the OEM spec for the exact model on the bid. The dB(A), the 23-foot distance, the side, and exercise vs full speed have to sit on the same page.
Measure the pad to each lot line and to the nearest bedroom window, then use the 6 dB doubling rule as a sanity check against the night number in your ordinance.
Read your town’s noise PDF for the nighttime residential number and whether standby exercise is exempt. Montgomery’s 55 dBA night / 65 dBA day pair, and the 57.5 dBA practical target with the meter allowance, are one county.
Put the weekly exercise window in writing, in allowed hours, before anyone pours the pad.
If the open-air math still overshoots the night cap at your lot line, price a farther pad or a different machine in the same week, and compare that number to a battery if your outage is hours rather than days.
Keep fire and CO on the placement guide. A quiet alcove that dumps exhaust at a window is still the wrong rectangle.
Hire the install that names the 23-foot sticker, the lot line, and the exercise window on the same page.