How loud is a standby generator?

What 65 dB sounds like

Decibels are logarithmic: a 10 dB increase sounds roughly twice as loud, not ten percent louder. Cummins publishes this reference scale in its dealer material:

At 65 dB, an air-cooled unit running the house is 15 dB above conversation and 25 dB below a lawn mower on that scale. You will hear it from the patio.

Published levels, model by model

These are the figures Cummins publishes in its dealer listing guide, all measured at 23 feet. Check the enclosure column before comparing two rows: the figures are not all measured with the same enclosure.

Air-cooled, 13kW to 20kW

The whole air-cooled line carries the same figure. The 13kW to 20kW units share one enclosure and one engine, so a larger air-cooled unit is not louder on paper than a smaller one.

Liquid-cooled, 25kW to 100kW

Enclosed diesel, 20kW to 100kW

Diesel is louder than gas at the same rating: the C30D6 is published at 69.7 dB(A) against 60 dB(A) for the RS30, both with the Sound Level 2 enclosure. Diesel engine noise is also lower in pitch, and low-frequency sound carries further and passes through walls more easily than the A-weighted figure suggests.

The number at your neighbor's fence, not at the machine

Published levels are measured at 23 feet. Sound in open air falls about 6 dB every time the distance doubles, so the level at a property line or a bedroom window is lower:

Treat those as the optimistic case. A real yard has fences, masonry and a house that reflect sound, and none of that is in the arithmetic. As a guide, a 65 dB unit is about 59 dB at 46 feet in open air.

Noise ordinances

Each city sets its own limit, quiet hours and measurement point, and many measure at the property line of the receiving property rather than at the equipment. Read your city's ordinance for two things: the limit that applies to your zoning, and whether emergency equipment running during a power failure is exempt. During an outage is the only time a standby generator runs for long.

Outside an outage, the unit runs only for its weekly exercise, which happens when the neighborhood is otherwise quiet. Scheduling it sensibly is the simplest way to avoid a complaint.

Limits, measurement points and quiet hours vary by city, and an HOA can impose something stricter than the municipality. We cover the deed-restriction side separately in HOA generator rules in Texas, and permitting city by city in city permit rules.

Three things that change the answer more than the model does

Where it sits. An air-cooled unit can be installed as close as 18 inches from the house, which is convenient and not always the quietest choice. A narrow side yard between two hard walls behaves like a speaker cabinet aimed at whoever is on the other side of the fence. An open back corner with the air discharge pointed away from the neighboring bedrooms is a different machine in practice.

When it exercises. This is the easiest thing to change. Set the exercise for a weekday mid-morning. The schedule can be changed remotely at any time; see remote monitoring.

Whether it needs to start at all. Crank-only exercise mode turns the engine over to run diagnostics without starting it, which Cummins says reduces wear, fuel use and exercise noise. It does not replace running the machine periodically, but it makes most weekly exercises quiet.

Summary

For an air-cooled home standby unit at 65 dB(A) at 23 feet, placement and the exercise schedule make more difference to the neighbors than the choice of model.

From 50kW up, and on any diesel unit, plan for noise from the start and specify the Sound Level 2 enclosure.